The response to western wheatgrass and needle- and thread grass to grasshopper defoliation
by Wayne Hunter Burleson
A thesis submitted in partial fulfillment of the requirements for the degree of MASTER OF SCIENCE
in Range Science
Montana State University
© Copyright by Wayne Hunter Burleson (1976)
Abstract:
A study of plant growth response to various intensities of defoliation by grasshoppers was conducted to
determine the influence of herbage removal on vigor and growth patterns of two common range
grasses, western wheatgrass (Agropyron smithii) and needle-and-thread (Stipa comata). Greenhouse
and field data indicated that increased grazing intensities significantly decreased root growth, tillering,
rhizome production and regrowth. It was also determined on a Montana rangeland site that the major
portion of grasshopper defoliation occurred after cessation of active growth of the two grass species
studied. STATEMENT OF PERMISSION TO COPY
In p re s e n tin g t h is th e s is in p a r t ia l f u l f i l l m e n t o f th e r e q u ir e ­
ments f o r an advanced degree a t Montana S ta te U n iv e r s it y , I agree
t h a t th e L ib r a r y s h a ll make i t
f r e e ly a v a ila b le f o r in s p e c tio n .
I
f u r t h e r agree t h a t p e rm is s io n f o r e x te n s iv e co p ying o f t h is th e s is
f o r s c h o la r ly purposes may be g ra n te d by my m a jo r p r o fe s s o r , o r ,
in h i s absence, by th e D ir e c to r o f L ib r a r ie s .
I t is
understood t h a t
any copying o r p u b lic a tio n o f t h is th e s is f o r f in a n c ia l gain s h a ll
n o t be a llo w e d w ith o u t my w r it t e n p e rm is s io n .
Si on a tu re
Date
(
a
uJLh
(3 (=
THE RESPONSE OF WESTERN WHEATGRASS AND NEEDLE-AND-THREAD
GRASS TO GRASSHOPPER DEFOLIATION
by
WAYNE HUNTER BURLESON
A th e s is s u b m itte d in p a r t ia l f u l f i l l m e n t
o f th e re q u ire m e n ts f o r th e degree
of
MASTER OF SCIENCE
in
Range Science
Approved:
"C h a irp e rs o n ^ 'G ra duate Committee
Head, M a jo r Departm ent
G raduate Dean
MONTANA STATE UNIVERSITY
Bozeman, Montana
September, 1976
iii
ACKNOWLEDGMENTS
My g r a t it u d e and a p p re c ia tio n a re expressed to Mr. G. B. H e w itt,
Dr. G. F. Payne, and Dr. T. W. Weaver f o r t h e i r guidance and encourage
ment th ro u g h o u t my d ata c o lle c t io n .
I a ls o express my a p p re c ia tio n
to Mr. W. C. L e in in g e r , Dr. N. L. Anderson, and Dr. J . E. T a y lo r
f o r t h e i r a d v ic e and su g g e s tio n s w ith th e m a n u s c rip t.
An acknowledgment o f indebtedn ess is made to th e U .S .D .A .
A .R .S . Rangeland In s e c t L a b o ra to ry and s t a f f f o r a llo w in g me to
g a th e r da ta w h ile employed as a re se a rch te c h n ic ia n .
TABLE OF CONTENTS
Page
V I T A ...................................................................................
ii
ACKNOWLEDGEMENTS .........................................................
iii
.....................................................
iv
LIST OF TABLES .............................................................
vi
TABLE OF CONTENTS
LIST OF F IG U R E S ................................................ ....
.
ix
ABSTRACT ..........................................................................
INTRODUCTION.........................................................
LITERATURE REVIEW
. . . . . . . .
• .
1
2
.................
'
D is t r ib u t io n and Im portance ..................
viii
,
2
..................
3
D e f o lia t io n S tu d ie s ...................................
5
G rasshopper G razing ......................
7
Roat Growth C h a r a c te r is tic s
DESCRIPTION OF FIELD STUDY AREA
. . .
..................
METHODS AND PROCEDURES . ...............................
Greenhouse Study
N eedle-and-Thread
10
14
14
Greenhouse Study — W estern W heatgrass
16
F ie ld Study — N eedle-and-T hread
. .
18
P la n t and G rasshopper Growth Curves .
21
V
Page
RESULTS AND DISCUSSION
...................................................................... 22
Needle-and-Thread- D e f o lia t io n
W estern Wheatgrass D e fo lia tio n
.................. . . . . . . . . . .
. . . . . .
..........................
P la n t and ,Grasshopper Development in th e F ie ld
SUMMARY AND CONCLUSIONS............................... . . .
. LITERATURE. CITED
22
.
...................... 52
. . ' .................................. 57
..................................................................59
34
L IS T OF TABLES
P age
T able I
Three y e a r summary o f m o n th ly p r e c ip it a t io n
(c e n tim e te rs ) near th e Three Forks Study
S ite .
Data were ta ke n a t T r id e n t, M o n ta n a ...................... 11
T a b le 2
Three y e a r summary o f m o n th ly te m p e ra tu re s
(degrees C e ls iu s ) near th e Three Forks Study
S ite .
Data were ta ke n a t T r id e n t, Montana . . . . . . .
12
Dry w e ig h ts (g m /p la n t) o f h e e d !e -a n d -th re a d
to p grow th re m a in in g a f t e r 48 days o f
g ra ssho pper d e f o lia t io n (greenhouse) ...................................
25
Dry w e ig h ts (g m /p la n t) o f n e e d !e -a n d -th re a d
r o o t grow th in response to grasshopper
d e f o lia t io n (greenhouse) .............................................................
26
Dry w e ig h ts (g m /p la n t) o f n e e d le -a n d -th re a d crown
(base p lu s 7 .5 cm o ld r o o ts ) grow th as r e la te d
to grassho pper d e f o lia t io n (greenhouse)
..........................
27
W eights (g m /p la n t) o f n e e d le -a n d -th re a d to p grow th
re m a in in g a f t e r a p p ro x im a te ly 40 days o f
g ra ssho pper d e f o l ia t io n ( f i e l d d a ta ) ...................................
31
W eights (g m /p la n t) o f n e e d le -a n d -th re a d ro o ts
in response to g ra ssho pper d e f o lia t io n ( f i e l d d a ta ) .
.
32
W eights (g m /p la n t) o f n e e d le -a n d -th re a d crowns
in response t o grassho pper d e f o lia t io n ( f i e l d d a ta ) .
.
33
T able 3
T ab le 4
T ab le 5
T ab le 6
T ab le 7
T ab le 8
T ab le 9
W eights (gm/4 p la n ts ) o f western- w heatgrass
to p grow th as r e la te d to grasshopper d e f o lia t io n
and c l i p p i n g ........................................................................................37
T ab le 10
W eights (gm/4 p la n ts ) o f w estern w heatgrass
ro o ts in response to grasshopper d e f o lia t io n
and c l i p p i n g ........................................................................................38
vi i
Page
Table 11
Table 12
T able 13
Table 14
Table 15
W eights (gm/4 p la n ts ) o f w e ste rn w heatgrass
crowns in response to grassho pper d e f o lia t io n
and c l i p p i n g ......................................................... : .........................
41
W eights (gm/4 p la n ts ) o f w e ste rn w heatgrass
rhizom es in response to grassho pper d e f o lia t io n
and, c l i p p i n g ........................................
. . . . . .
42
.
.
Maximum depth o f p e n e tr a tio n (cm) o f w e s te rn
w heatgrass ro o ts in response to grasshopper
d e f o lia t io n and c lip p in g .............................................................
45
Number o f new shoots produced by w e stern
w heatgrass in response to grasshopper
d e f o lia t io n and c l i p p i n g ................................................ ' . . .
51
Developm ental stages o f grassho pper sp e cie s
from th e Three F o rk s , Montana stu d y s i t e — 197b . . .
55
L IS T OF FIGURES
Page
F ig u re I
Root boxes used in greenhouse s t u d i e s .................................
15
F ig u re 2
Caged n e e d !e -a n d -th re a d p la n t . . . .
................................
20
F ig u re 3
Top and r o o t w e ig h ts o f n e e d !e -a n d -th re a d
grass f o llo w in g 48 days o f grasshopper
d e f o lia t io n
.............................................................
24
Top and r o o t w e ig h ts o f n e e d !e -a n d -th re a d
fo llo w in g a p p ro x im a te ly 40 days o f
grassho pper d e f o lia t io n ( f i e l d d a ta )
......................
. .
30
Top and r o o t w e ig h ts o f w e ste rn w heatgrass
in r e la t io n s h ip to c lip p in g and grassho pper
d e f o l i a t i o n ........................................................................................
36
Crown and rhizom e w e ig h t response o f
w e ste rn w heatgrass to c lip p in g and
grassho pper d e f o lia t io n
...........................................................
40
Maximum r o o t depth response o f w e stern
w heatgrass to g ra ssho pper d e f o lia t io n
and c l i p p i n g .......................... ........................................................
44
Root grow th r a te o f w e ste rn w heatgrass
in response to grasshopper d e f o lia t io n
and c l i p p i n g .....................
47
Top grow th response o f w e stern w heatgrass
to c l i p p i n g .................................................................................
48
The t o t a l new shoots produced by w e ste rn
w heatgrass in response t o c lip p in g and
grassho pper d e f o lia t io n
. . . : .............................................
50
Average and range o f culm h e ig h t f o r
w e ste rn w heatgrass as r e la t e d to
grassh o p p e r developm ent
...........................................................
53
Average and range o f culm h e ig h t f o r n e e d le -a n d th re a d as r e la te d to grassho pper d e f o l ia t io n
. . . .
54
F ig u re 4
F ig u re 5
F ig u re 6
F ig u re 7
F ig u re 8
F ig u re 9
F ig u re 10
F ig u re 11
F ig u re 12
ix
ABSTRACT
I
I
I
I
I
I
1
I
I
I
-
'I
:
A s tu d y o f p la n t grow th response to v a rio u s in t e n s it ie s o f
d e f o lia t io n by grasshoppers was conducted to d e te rm in e th e in flu e n c e
o f herbage removal on v ig o r and grow th p a tte rn s o f two common range
g ra s s e s , w e ste rn w heatgrass ( Agropyron s m i t h i i ) and n e e d le -a n d -th re a d
( S tip a com ata) .
Greenhouse and f i e l d d a ta in d ic a te d t h a t in c re a s e d
g ra z in g in t e n s it ie s s i g n i f i c a n t l y decreased r o o t g ro w th , t i l l e r i n g ,
rhizom e p ro d u c tio n and re g ro w th .
I t was a ls o de te rm in e d on a
Montana ra n g e la n d s i t e t h a t th e m a jo r p o r tio n o f grasshopper d e f o lia t i on o c c u rre d a f t e r c e s s a tio n o f a c t iv e grow th o f th e two grass
sp e cie s s tu d ie d .
INTRODUCTION
The v a rie d and pronounced e f f e c t s o f d e f o lia t io n on grass p la n ts
sh o u ld d e te rm in e in p a r t th e b a s is f o r sound judgm ent in managing
f o r th e y ie ld and q u a lit y o f g ra s s la n d p r o d u c t iv it y .
There are
d e ta ile d , s tu d ie s o f th e in flu e n c e o f hand c lip p in g and g ra z in g by
liv e s t o c k on ra nge land fo ra g e s p e c ie s .
Y e t, l i t t l e
is known abo ut th e
e f f e c t s o f in s e c t d e f o l ia t io n , s p e c i f i c a l ly grasshoppers on in d iv id u a l
grass p la n ts .
Rangeland grassho pper s tu d ie s have d e a lt p r im a r ily w ith d i r e c t
fo ra g e lo sse s and n o t w ith th e lo n g -te rm e f f e c t s o f grasshopper
d e f o lia t io n .
Research is needed on t h is l a t t e r component o f th e grass
la n d ecosystem .
S tu d ie s re p o rte d h e re in were conducted under bo th greenhouse
and f i e l d
c o n d itio n s to a s c e r ta in th e in flu e n c e o f grasshopper g ra z in g
on w e ste rn w heatgrass ( A gropyron s m i t h i i ) and n e e d !e -a n d -th re a d
( S ti pa com ata).
LITERATURE REVIEW
D is t r ib u t io n and Im portance
W estern W heatgrass
W estern w heatgrass is an im p o rta n t p e re n n ia l n a tiv e rh izo m a to u s
grass d is t r ib u t e d g e n e r a lly th ro u g h o u t th e U n ite d S ta te s e xce p t in
th e humid s o u th e a s te rn s ta te s .
I t is most abundant in the n o rth e rn
and c e n tr a l p a rts o f th e G rea t P la in s and is o fte n th e dom inant grass
o ve r la rg e areas (U. S. F o re s t S e r v ., 1937).
W estern w heatgrass is
a l k a l i - t o l e r a n t and grows in dense patches in w e ll- d r a in e d bottom
la n d s .
I t may a ls o be found on open p la in s and in n e a rly pure stands
on abandoned d ry la n d farm s in Montana (U. S. Dep. A g r . , 1948).
W estern w heatgrass is a v a lu a b le fo ra g e p la n t f o r a l l c la s s e s
o f liv e s t o c k and is c o n s id e re d c h o ic e fo ra g e f o r e lk and deer (U. S.
F o re s t S e r v ., 193 7).
I t cures w e ll on th e g ro u n d , thus making h ig h
q u a lit y w in t e r fo ra g e and hay.
W estern w heatgrass has been used to
some e x te n t f o r r e v e g e ta tio n ; seed a v a i l a b i l i t y
is adequate.
( V a lle n t i n e , 1974).
N eedle -a n d -th re a d
Needle -a n d -th re a d is a d e e p -ro o te d , lo n g - liv e d , n a tiv e bunchgrass w hich o ccurs on w e ste rn U n ite d S ta te s ranges and is most
abundant on sandy s o ils o f th e N o rth e rn G re a t P la in s (U. S. Dep.
3
A g r . , 1948).
I t may be found in a lm o st pure stands in an advanced
sta g e o f secondary su cce ssio n on abandoned f i e l d s
(B o o th , 1950).
The fo ra g e v a lu e o f n e e d le -a n d -th re a d v a r ie s w ith r e g io n s ,
season o f g ro w th , and p la n t a s s o c ia tio n .
I t is c u t f o r hay in p a rts
o f Wyoming,' N o rth D akota, South D akota, and Nebraska where i t
ra te s
as v e ry good fo ra g e (U. S. F o re s t S e r v ., 1937). ' T h is grass p ro v id e s
e a r ly s p rin g fo ra g e o v e r much o f e a s te rn Montana b u t due to th e s t i f f
tw is te d awns, m echanical in ju r y to liv e s t o c k can o c c u r a t seed
m a tu r ity (B o o th , 1950).
Root Growth C h a r a c te r is tic s
Both w e ste rn w heatgrass and n e e d le -a n d -th re a d are cool season
g ra s s e s .
T h e ir p r in c ip a l grow th p e rio d is
in th e c o o l, m o is t s p rin g
w ith decrease o r c e s s a tio n o f grow th d u rin g th e summer.
Optimum
te m p e ra tu re f o r grow th and n e t p h o to s y n th e s is by tem perate grass
sp e cie s ranges from 20° to 25° C (W h ite , 1973).
M u e lle r (1941) in d ic a te d t h a t r o o t grow th f o r w e stern w heatgrass
c o in c id e s w ith to p g ro w th .
A c tiv e ro o ts are w h ite in c o lo r and v a ry
from 0 .2 to 1 .0 mm in d ia m e te r.
The th in n e r r o o ts r a r e ly exceed
30 cm in le n g th and o fte n grow h o r iz o n t a lly w h ile th e t h ic k e r ro o ts
p e n e tra te v e r t i c a l l y b u t branch le s s d e n s e ly .
Depth o f r o o tin g
v a r ie s c o n s id e ra b ly w ith c lim a te , s o i l , and to p o g ra p h y (Coupland
and Johnson, 1965).
Weaver (1942) determ ined th e average r o o t
4
grow th r a te o f young w e ste rn w heatgrass p la n ts to be 8 .4 mm/day f o r
a th re e -m o n th p e r io d .
I t s maximum r o o tin g depth in Nebraska and
Kansas ranged from 2.1 to 3 .6 m w h ile a v e ra g in g 1 .5 m in th e more
a r id p o r tio n s o f th e w e ste rn U n ite d S ta te s (W eaver, 1958).
Hopkins (1953) found t h a t th e lo w e r ro o ts add l i t t l e
t o t a l w e ig h t o f th e r o o t system .
to th e
He in d ic a te d t h a t in w estern
w heatgrass o n ly 15 p e rc e n t o f th e t o t a l r o o t w e ig h t o ccu rre d below
th e 30 cm l e v e l „
Weaver (1947) found t h a t r o o t decay was somewhat v a r ia b le w ith
s p e c ie s .
W estern w heatgrass had a tendency f o r le s s ra p id decay than
o th e r sp e cie s s tu d ie d and a fe w -ro o ts r e ta in e d t e n s ile s tre n g th f o r
th re e y e a r s .
Weaver and Z in k (1946) in d ic a te d r o o t s u r v iv a l f o r
w e ste rn w heatgrass was 42 p e rc e n t o f tagged r o o ts a f t e r th e second
summer.
N e e d !e -a n d -th re a d is m o st e x te n s iv e ly ro o te d in l e v e l , s t a b il iz e d
sand, where r o o tin g depth reaches 150 cm w ith a la t e r a l spread o f
35 cm.
A c tiv e ro o ts a re cream c o lo re d w ith two to seven main r o o ts
s u p p o rtin g each sh o o t o f th e bunch (Coupland and Johnson, 1965).
In a stu d y by Weaver (1 9 5 8 ), n e e d !e -a n d -th re a d r o o ts were more p ro ­
f u s e ly branched and c ris s c ro s s e d when compared to w e stern w heatgrass
r o o ts .
5
D e f o lia t io n S tu d ie s
Past c lip p in g s tu d ie s (A ld o u s , 1930; B is w e ll and Weaver, 1933;
B la is d e ll and Pechanec, 1949; Wagner, 1952, A lb e rts o n e t a l , 1953;
H e in ric h s and C la r k , 1950; Pond, 1961) have in d ic a te d t h a t w ith
in c re a s in g fre q u e n c y and amount o f p la n t t is s u e removed by c lip p in g
th e re is g e n e r a lly a decrease in grass p r o d u c t iv it y .
Branson (1956)
found t h a t r o o t p ro d u c tio n was a ffe c te d more d e t r im e n t a lI y than to p
p ro d u c tio n in r e la t io n s h ip to to p grow th re m o val.
In c o n tr a s t to
th e above s t u d ie s , Leopold (1949) found t h a t c lip p in g s tim u la te d th e
p ro d u c tio n o f t i l l e r s .
In a Wyoming s tu d y by Baker and Hunt (1 9 6 1 ),
in te r m e d ia te w heatgrass and pubescent w heatgrass c lip p e d a t 10 cm
produced s i g n i f i c a n t l y more t i l l e r s
than th o se c lip p e d a t 5 cm.
Changes in p la n t s t r u c t u r e induced by p ro lo n g e d heavy g ra z in g
o f n e e d le -a n d -th re a d appear to fa v o r p e rs is te n c e (P e te rs o n , 19 6 2 ).
Changes were as f o llo w s :
(I)
r e l a t i v e l y r a p id re g ro w th a f t e r c l i p ­
p in g , (2 ) g re e n e r and more v ig o ro u s s h o o ts , (3 ) m aintenance o f m oderate
ca rb o h yd ra te , re s e rv e le v e ls ,
and more p r o s tr a te g ro w th .
(4 ) slo w e r s p r in g g ro w th , (5 ) a s h o r t e r
Hanson e t a l (1931) found t h a t w e ste rn
w heatgrass in c re a s e d more under c o n tin u o u s g ra z in g than under p ro ­
t e c t io n from g ra z in g .
In a re v ie w , Jameson (1963) s ta te d t h a t , g e n e r a lly , r o o t
p ro d u c tio n was u n iv e r s a lly depressed when d e f o l ia t io n o c c u rre d ,
6
w h ile th e y ie ld o f above ground p a rts was somewhat e r r a t i c .
C rid e r
(1955) re p o rte d t h a t removal d u rin g th e grow ing season o f h a lf o r
more o f th e f o lia g e o f bo th cool and warm season grass species
( in c lu d in g bunch, rh iz o m a to u s , and s t o lo n if e r o u s ty p e s ) caused r o o t
grow th to s to p f o r a p e rio d o f tim e a f t e r each rem o val.
Root grow th
stoppage u s u a lly o c c u rre d w it h in 24 hours and c o n tin u e d u n t i l tops
re c o v e re d .
it
C r id e r (1955) p re se n te d th e fo llo w in g d a ta :
P e rce n t Top
Removal
P e rce n t Root
Stoppage
No. Days Complete
Root Stoppage
90
100
80
100
12
70
78
0
60
50
0
50
2
0
.
17
. No r o o t stoppage was in d ic a te d in t h is s tu d y from a to p re d u c tio n
o f 40 p e rc e n t o r le s s .
A s tu d y by P arker and Sampson (1931) showed
t h a t a s in g le h a rv e s t o f f o lia g e r e s u lte d in te m p o ra ry c e s s a tio n o f
r o o t grow th in s o f t chess ( Bfomus hordeaceus) and p u rp le n e e d le g ra ss
( S tip a p u lc h r a ) .
T h is c e s s a tio n was fo llo w e d by an im m ediate in c re a s e
in grow th o f th e to p s .
Branson (1953) l i s t e d two f a c to r s w hich a f f e c t th e r e s is ta n c e
o f grasses to g r a z in g :
(I)
th e h e ig h t to w hich th e grow ing p o in t
( a p ic a l m e riste m ) is r a is e d , and (2). th e r a t i o o f f e r t i l e
culms
I
I
to v e g e ta tiv e cu lm s.
H is s tu d ie s found t h a t th e v e g e ta tiv e culms
o f w e ste rn w heatgrass ra is e d t h e i r grow ing p o in ts from 16 cm in June
t o 40 cm in Septem ber.
T h is w ould a llo w f o r t h e i r grow ing p o in ts
to be removed by g ra z in g so t h a t no new le a ve s would be produced
by th o se culm s.
He a ls o noted t h a t removal o f th e i n f lo re sce n se s
has an e f f e c t s im il a r to removal o f e le v a te d grow ing p o in ts .
G rasshopper G razing
G rasshopper damage to ra n g e la n d has been an economic concern
in th e U n ite d S ta te s s in c e th e e a r ly 1800's (P a rk e r and Connin , 1964)
Cowan (1958) l i s t e d grasshoppers in th e U n ite d S ta te s as b e in g in
th e upper 10 most tro u ble som e in s e c t pe sts to a g r ic u lt u r e .
In an
A riz o n a s tu d y , Nerney (1958) found grasshoppers to be in d i r e c t
c o m p e titio n w ith liv e s t o c k f o r a v a ila b le fo ra g e and were a t le a s t
p a r t ly re s p o n s ib le f o r th e d e c lin e in p r o d u c t iv it y o f s h o rtg ra s s
ra n g e la n d s .
He found t h a t p r e fe rr e d h a b ita ts o f economic grassho pper
sp e cie s were a s s o c ia te d w ith poo r ra n g e la n d s .
These poor range land s
were g e n e r a lly dom inated by lo w -g ro w in g weeds.
In th e p a s t, many p u b lis h e d e v a lu a tio n s o f grasshopper damage
in r e la t io n to range land v e g e ta tio n lo sse s have been to o g e n e ra liz e d .
Anderson (1972) in d ic a te d d i f f i c u l t i e s
damage s tu d ie s as f o llo w s :
in in t e r p r e t in g data from
changes in d e n s ity o f grasshopper
p o p u la tio n s , uneven fe e d in g p a t t e r n s , n o n -r a n d o m .d is tr ib u tio n o f
8
v e g e ta tio n and g ra s s h o p p e rs , v a rie d fo o d - p la n t p re fe re n c e and food
s e l e c t i v i t y w it h in p la n t s p e c ie s , and a la c k o f knowledge c o n c e rn in g
p la n t grow th phenomena as r e la te d to d e f o lia t io n .
Newton and Esselbaugh (1952) s ta te d t h a t when grasshoppers feed
on p la n t m a te ria l near th e ground th e y c o n t r ib u te to o v e rg ra z in g ,
'f
weakening o f th e r o o t re s e rv e s , and may p o s s ib ly be p r o v id in g a way
f o r l a t e r s o il e ro s io n .
New Zealand grasshoppers a re b a s ic a lly lo w -
volume g ra z e rs b u t because o f t h e i r s e le c tiv e fe e d in g h a b its th e y
can e x e r t h ig h g ra z in g p re s s u re on c e r ta in p la n t sp ecies (W h ite , 1974)
I
Cowan (1958) s ta te d t h a t damage to ra n g e la n d v e g e ta tio n is
governed by th e grassho pper s p e c ie s , th e v e g e ta tio n com plex, th e
number o f g ra ssh o p p e rs, and. th e w e a th e r.
I
I
I
p o s s ib le :
(I)
Three typ e s o f damage are
removal o f fo ra g e in d ir e c t c o m p e titio n w ith liv e s t o c k ,
(2 ) permanent damage to p la n ts due to c o n tin u e d fe e d in g by g ra s s ­
hoppers beyond p e rc e n t use f a c t o r s , and (3 ) d e s tr u c tio n o f seed heads.
However, n o t a l l grasshopper damage s tu d ie s have in d ic a te d t h a t a
lo s s o f v e g e ta tio n r e s u lt s fro m grasshopper g ra z in g .
H a rris (1974)
e x p la in e d how sometimes no lo s s , o r even an in c re a s e in p la n t y i e l d ,
may come ab o u t due to in s e c t fe e d in g .
p la n ts may r e d ir e c t l i m i t i n g
I
and deve lop a s u r p lu s .
n u t r ie n t re so u rce s to undamaged t is s u e
A ls o , e a r ly removal o f a p ic a l dominance o f
grow ing p la n ts may s tim u la te t i l l e r i n g .
I
He s ta te d t h a t d e f o lia t e d
9
In a grassho pper damage s tu d y on Montana ra n g e la n d s , Anderson
(1961) found l i t t l e
c o r r e la t io n between numbers o f grasshoppers p e r
u n it area and lo s s o f v e g e ta tio n .
In a summary by Anderson (1 9 7 2 ),
c lip p in g e f f e c t s on v e g e ta tio n suggested th a t grasshoppers may be
re s p o n s ib le f o r permanent damage to. range land v e g e ta tio n , b u t he
a ls o in d ic a te d t h a t grasshoppers under c e r ta in circu m sta n ce s may
be re s p o n s ib le f o r in c re a s e s in fo ra g e p ro d u c tio n o v e r a p e rio d
o f y e a rs .
DESCRIPTION OF FIELD STUDY AREA
A s tu d y area was s e le c te d 12.8 km n o rth e a s t o f Three F o rk s ,
Montana in B roadw ater County.
from liv e s t o c k g ra z in g in 1973.
A 16 ha e x p e rim e n ta l s i t e was e x c lo se d
T h is s i t e had p r e v io u s ly been plow ed,
a p p ro x im a te ly 30 y e a rs e a r l i e r , and l a t e r abandoned.
The area is
lo c a te d on an upland bench w ith a two p e rc e n t s lo p e and a s o u th e a s t
exposure.
A sm a ll w a te r r u n - in area tra v e rs e s th e e x c lo s u re .
The s o i l ty p e is c la s s if ie d as a Brocko s e r ie s in th e mixed
fa m ily B o r o l li c C a lc io r t h id (SCS, N a tio n a l C o o p e ra tio n S o il S u rve y,
1972).
The t e x tu r e th ro u g h o u t th e p r o f i l e ranges fro m v e ry f in e
sandy loam to s i l t loam w ith 8 to 18 p e rc e n t noncarbonate c la y and
I to 14 p e rc e n t f in e sand t o c o a rs e r p a r t ic le s .
Brocko s o ils a re
form ed from e o lia n m a te ria l w hich has been d e p o s ite d o ve r o ld e r
r i v e r te r r a c e s .
The c lim a te is c o o l, semi a r id w ith an annual average p r e c ip i­
t a t i o n o f 3 0 .5 cm in w hich most o f th e p r e c ip it a t io n occurs d u rin g
th e s p rin g m onths.
Three ye a rs o f p r e c ip it a t io n and te m p e ra tu re
d a ta are summarized on Tables I and 2 r e s p e c t iv e ly .
These da ta
were recorded a t T r id e n t, Montana a p p ro x im a te ly 8 km s o u th e a s t o f
th e a c tu a l s tu d y s i t e .
TABLE I .
T hre e y e a r summary o f m o n t h ly p r e c i p i t a t i o n
(c e n tim e te rs )
n e a r t h e T hre e Forks S tu d y S i t e .
Data were t a k e n a t
T r i d e n t , Montana.
YEAR
MONTH
JAl"'
FE
MA
AP
AG
SE
OC
NO
DE
TOTAL/YEAR
-I
E4.70
E4.93
E2.30
.84
E 29 .57
3.81
1.02
1.09
4.42
.48
1.98
.8 9
.61
16.31
-2.2 6
-1 .1 4
-5 .5 4
-1.5 7
1 .4 7
-2.6 9
.20
-.3 6
-.2 2
-13.64
1.14
3.40
9 .30
7.70
7.01
3.12
.99
5 .7 4
.3 3
.5 8
4 2 .0 6
-.3 8
.7 6
4 .34
1.14
4.34
.1 8
-2.1 8
3 .9 6
-.91
-.2 5
12 .12
.76
.8 4
1.85
1974
T o ta l
P re c ip ita tio n
.03
.05
1.55
.3 8
D e v ia tio n
f r o m Mean
-.9 4
-.61
.0 3
T ota l
P re c ip ita tio n
1.45
1.30
.4 8
.6 4
I/
LI. S. D e p t , o f Commerce A d m i n i s t r a t i o n ,
V o l: 76,77,78
2/
Amount i s
N a tio n a l
LO
CO
2.71
.5 3
p a r t i a l l y e s tim a te d
JL
E .91
T ota l
P re c ip ita tio n
D e v ia tio n
f r o m Mean
JU
9 .17
1973
1975
MY
O c e a nic and A t m o s p h e r ic A d m i n i s t r a t i o n ,
E n v ir o n m e n t a l
Data S e r v i c e ,
^
\
TABLE 2.
T hre e y e a r suranary o f m o n t h ly t e m p e r a t u r e s ( d e g r e e s C e l s i u s )
n e a r t h e T hre e F o rk s S tu d y S i t e .
Data w e re ta k e n
a t T r i d e n t , M o n ta n a .—^
MONTH
YEAR
OA
FE
MA
AR
MY
JU
JL
AG
SE
OC
NO
DE
1973
Mean/Mo.
Max.Mean
Min.Mean
- 6.1
- 0 .3
-1 1 .9
- 4.7
-9 2 .3
-11 .9
3.1
9.1
-3 .0
5 .9
12.8
- 0 .9
12.2
21.3
2 .7
17.0
25.6
8.3
21.4
31.5
1 1 .3
20.9
30.8
11.1
13.3
20.9
5 .6
9 .2
1 7 .2
1.3
-0.1
4.7
-4 .8
0 .2
5 .7
-6 .2
1974
Mean/Mo.
Max.Mean
Min.Mean
- 6 .4
- 1.4
-1 1 .4
0 .1
5 .8
- 5.8
1.6
7 .6
-4.6
8 .6
14.9
2 .2
9.9
16.2
3.7
18.6
2 7.8
9 .4
2 1.8
31.6
12.0
17.0
25.0
8.9
12.4
22.6
2.3
8 .5
1 8 .2
-1.2
1.6
7.8
-4.7
-3.2
2.2
-8.6
MeanTmo.
Max.Mean
Min.Mean
-
1975
- 5 .9
0 .2
-11 .9
-9 .7
4.3
-5 .7
1 .6
7 .3
- 4 .2
10.0
17.2
2 .8
14.8
2 2.8
6 .2
21.7
30.4
1 2 :9
18.2
26.8
9 .4
1 3 .8
24.1
3 .5
7 .9
1 4 .5
1.3
-0.1
6.6
-6 .8
-1.3
4.3
-6.9
V
U. S.
5 .3
0.4
-11.1
‘
D e p t , o f Commerce, N a t i o n a l
O c e a nic and A t m o s p h e r ic A d m i n i s t r a t i o n ,
E n v ir o n m e n t a l Data S e r v i c e , V o l : 76, 7 7 , 78
13
The v e g e ta tio n is dom inated by w id e ly d is p e rs e d bunches o f n e e d le a n d -th re a d on th e r e l a t i v e l y le v e l, plowed p o r tio n s o f th e s tu d y s i t e .
O th e r v e g e ta tio n o c c u rrin g in th e sm a ll r u n - in area in w hich p la n t
grow th curves were measured was c h a ra c te riz e d o c u la r ly by th e fo llo w in g
sp e cie s in a p p ro xim a te o rd e r o f descending abundance:
w e ste rn w h e a t-
g ra s s , green n e e dle gra ss ( S t i pa v i r i d u l a ) , common d a n d e lio n
( Taraxacum o f f i c i n a l e ) , b lu e grama ( B outeloua g r a c i l i s ) , fr in g e d
sagew ort ( A rte m is ia f r i g i d a )., cudweed sagew ort ( A rte m is ia
J u d o v ic ia n a ) , and b ig sagebrush ( A rte m is ia t r i d e n t a t a ) .
sp e cie s p re s e n t in c lu d e :
O ther
death camas ( Zygadenus venenosus) ,
th r e a d le a f sedge ( Carex f i I i f o l i a ) , p r a i r i e ju n e g ra s s ( K o e le r ia
c r i s t a t a ) , bluebunch w heatgrass ( Agropyron s p ic a tu m ) , s a l s if y
( Tragcpogon d u b iu s ) , o b io n g le a f b lu e b e ll ( M e rte n s ia o b l o n g if o li a ) ,
A s tra g a lu s s p p . , Hood's .p h lo x ( P hlox h o o d il) , common s u n flo w e r
( H e lia n th u s annuus) , w o o lly p la n t a in ( P lantago p u r s h i i ) , b i s c u it
r o o t ( L o m a tiurn s p p .) , N u t t a ll v i o l e t ( V io la n u t t a l l i i ) , Fleabane
( E rlg e ro n s p p . ) , w h ite p o in tlo c o ( O x y tro p is s e r ic e a ) , and Rocky
M ountain i r i s
( Ir is
m is s o u r ie n s is ) .
METHODS AND PROCEDURES
Greenhouse Study — Needle-and -T h rea d
A group c o n s is tin g o f a p p ro x im a te ly equal s iz e ( o c u la r ly
s e le c te d — basa l d ia m e te r a p p ro x im a te ly 5 cm) bunches o f n e e d le a n d -th re a d p la n ts was removed from th e stu d y area in November o f
1973.
The to p s were trim m ed to 2 .5 cm le v e l and th e ro o ts trim m ed
to 8 cm.
The p la n ts were th e n p la ce d two each in f l a t m etal pans
and s to re d o u td o o rs in Bozeman, Montana u n t i l January 16, 1974.
Twelve p la n ts were then p la ce d one each in r o o t boxes f i l l e d w ith
a s ta n d a rd greenhouse s o i l m ix tu re c o n s is tin g o f 75 p a rts washed
sand and 25 p a r ts p e a t.
The r o o t boxes measured 60 x 29 x. 23 cm
and were c o n s tru c te d o f p in e wood w ith a s lo p in g rem ovable g la ss
f r o n t as shown, in F ig u re I .
The greenhouse a i r te m p e ra tu re ranged from 25° to 30° C and
th e s o i l te m p e ra tu re a t a depth o f 10 cm, measured in one r o o t box,
ranged from 18° to 26° C.
The p h o to p e rio d c o n s is te d o f n a tu ra l
day le n g th , w ith th e l i g h t d if f u s in g th ro u g h tr a n s p a r e n t, c o rru g a te d ,
f ib e r g la s s p a n e lin g .
A f t e r 72 days o f g ro w th , th e 12 p la n ts in th e v e g e ta tiv e s ta te
were random ly d iv id e d in t o th e fo llo w in g th re e tre a tm e n ts :
caged
grasshoppers re p re s e n tin g a heavy g ra z in g , m oderate g ra z in g , and
caged p la n ts w ith no grasshoppers ( c o n t r o l) .
A t th e i n i t i a t i o n
FIGURE I .
Root boxes used in greenhouse s tu d ie s
o f th e tre a tm e n ts 3rd in s t a r M elanoplus s a n g u in ip e s were p laced a t
th e ra te s o f . 12, 3 and O grasshoppers p e r cage re p re s e n tin g th e
th re e tre a tm e n ts .
A group o f th e equal age grasshoppers was used
as repla cem ents t o m a in ta in th e grass d e f o l ia t io n le v e ls .
The
grassh o p p e r d e n s itie s in each cage were p e r io d ic a lly a d ju s te d to
e s ta b lis h equal d e f o l ia t io n . w it h in bach tre a tm e n t.
One week b e fo re grassho pper in t r o d u c tio n o n to th e 72-day p la n t s ,
an a d d it io n a l 12 p la n ts were s t a r t e d in r o o t boxes to d e te rm in e th e
e f f e c t s o f g ra ssho pper g ra z in g on new green-up g ro w th .
These 12
p la n ts were random ly d iv id e d in t o th re e tre a tm e n ts o f 3 , I , and O
M. s a n g u in ip e s in an a tte m p t to d u p lic a te th e p r e v io u s ly m entioned
g ra z in g in t e n s i t i e s .
No r o o t grow th measurements were made in t h is
phase o f th e s tu d y .
On May 16, 1974, th e t e s t was ended and th e p la n ts were washed
from th e r o o t boxes and d iv id e d in t o r o o t , cro w n s , and to p g ro w th .
L a te r th e y were o v e n -d rie d a t 60° C and w eighed.
In t h is phase o f
th e s tu d y , crown c o n s is te d o f th e v e ry basal area o f th e culm th ro u g h
8 cm o f r o o t s .
I
Greenhouse S tudy — W estern W heatgrass
A p p ro x im a te ly 400 w e ste rn w heatgrass (Av s m it h ii v a r. rosana)
seeds were p la ce d on wet b l o t t e r paper in f o u r p e t r i dish e s on
March I ,
1975.
W ith in f iv e days th e seeds g e rm in a te d .
G e rm in a tio n
I
17
day was day one in th e e x p e rim e n t.
On day tw o , 100 s e e d lin g s o f
u n ifo rm s iz e and v ig o r were t r a n s fe r r e d in t o 25 o f th e g la s s faced
r o o t boxe s.
The fo u r s e e d lin g s p e r box were p la c e d one cm from th e
s la n t in g g la s s .
I l
The s o i l used in t h is e x p e rim e n t was mixed by hand u sin g
% washed sand and ^ Bozeman s i l t
loam.
by steam f o r 24 h o u rs .
boxes were la i d on t h e i r s id e s and
f ille d
The r o o t
w ith th e mixed s o i l .
The loam was s t e r i l i z e d
S if t e d s o il was p la ce d n e x t to th e g la s s
and form ed th e to p la y e r o f each r o o t box.
The r o o t boxes were
h e a v ily w a te re d and l e f t u n t i l th e s o i l was s e t t le d on th e g la s s .
Care was taken n o t to push th e s o i l a g a in s t th e g la s s because t h is
causes, a muddy sm earing e f f e c t .
Small
s o i l and sand p a r t ic le s
sh o u ld j u s t r e s t on th e g la s s f o r th e b e s t vie w o f th e r o o t system s.
On day 31, th e 25 r o o t boxes each c o n ta in in g th e fo u r w e ste rn
w heatgrass p la n ts were random ly d iv id e d in t o f i v e tre a tm e n ts , each
h a vin g f i v e
m ents.
r e p lic a tio n s ,.
A d ie
was used to random ly a ssig n t r e a t ­
T h is re p re s e n te d a com ple te randomized b lo c k d e s ig n .
f i v e tre a tm e n ts were as f o llo w s :
1.
C lip p in g a t one tim e on day 31
2.
Heavy g ra z in g by grassho ppers (80 p e rc e n t removal by
w e ig h t o f to p g ro w th )
3.
M oderate g ra z in g by grasshoppers (50 p e rc e n t rem oval)
?
The
18
4.
L ig h t g ra z in g by grasshoppers (20 p e rc e n t re m o v a l)
5.
Un-grazed
The g ra z in g le v e ls were m a in ta in e d f o r a p e rio d o f 16 days '
by th e g ra ssho pper M elanoplus b i v i t a t t u s .
The grassho pper d e n s itie s
were p e r io d ic a lly changed to e s ta b lis h equal le v e ls o f d e f o lia t io n
w it h in a tre a tm e n t.
T h is a llo w e d th e grasshoppers to s lo w ly e s ta b lis h
th e d e fin e d le v e ls o f d e f o lia t io n s .
The c lip p in g tre a tm e n t removed
a l l p o r tio n s o f th e p la n t above th e f i r s t le a f , le a v in g a s tu b b le
h e ig h t o f about 2 .5 cm.
The g ra z in g tre a tm e n t ended on day 48, a f t e r
w hich th e p la n ts c o n tin u e d to grow u n t i l day 93.
Data were c o lle c t e d p e r io d ic a lly on h e ig h t o f to p grow th a lo n g
w ith a i r and s o i l te m p e ra tu re s .
D a ily r o o t grow th measurements were
made j u s t p r io r to and d u rin g th e tre a tm e n t p e r io d .
tille r s
The number o f
and shoo ts from rhizom es was recorded f o r each r o o t box.
On day 93 th e p la n ts were s e p a ra te d in t o to p s , crow ns, r o o ts , and
rhizom es and were oven d r ie d a t 60° C and w eighed.
The crown con­
s is te d o f th e im m ediate basal p o r tio n o f th e culm and sm all (5 mm)
p o r tio n s o f th e r o o ts .
F ie ld Study - - N eed!e-and-Thread
A fie ld
s tu d y com paring n e e d !e -a n d -th re a d p la n ts s u b je c te d to
g ra ssho pper g ra z in g and p la n ts l e f t ungrazed was conducted a t th e
s tu d y s i t e near Three F o rk s , Montana.
Ten somewhat is o la t e d p la n ts
19
o f a p p ro x im a te ly th e same s iz e (b a s a l d ia m e te r a p p ro x im a te ly 5 cm)
were s e le c te d and excavated on June 20, 1974.
The r o o t system was
c u t 8 cm below th e s u rfa c e le v e l, and th e f la g le a f and sheath con­
t a in in g th e in flo r e s c e n c e were removed.
These p la n ts were then
re p la n te d in t h e i r o r ig in a l s p o t and caged as shown in F ig u re 2.
F iv e random ly s e le c te d caged p la n ts were then in f e s t e d , each w ith
s ix 3rd and 4 th in s t a r grasshoppers ( A u loca ra e l l i o t t i ) .
re m a in in g caged p la n ts were used as c o n t r o ls .
The f i v e
D u rin g t h is t e s t , th e
grasshoppers were m a in ta in e d .a t a le v e l o f a t le a s t two grasshoppers
p e r cage.
A o th e r group o f ten n e e d le -a n d -th re a d p la n ts was s im il a r ly ,
s e le c te d a lth o u g h n o t e xca va te d .
w ith A. e l I i o t t i
These p la n ts were caged and in fe s te d
a t th e same le v e l as th e above.
A f t e r 48 days th e re were no grasshoppers re m a in in g on th e
tre a te d p la n ts .
The p la n ts were th e n excavated w ith a shovel in
a p p ro x im a te ly equal s iz e , b lo c k s (15 x 15 x 30 cm ), la b e le d , and b ro u g h t
in t o th e la b o r a to r y f o r s o il re m o va l.
A f t e r p re s o a k in g th e p la n ts
in a la rg e tu b o f w a te r, th e s o i l was g e n tly a g ita te d w ith ru n n in g
w a te r to remove th e re m a in in g s o i l p a r t ic le s .
The p la n ts were then
se p a ra te d in t o to p s , crow ns, and ro o ts and w eighed fo llo w in g oven­
d ry in g f o r 24 h o u rs .
The crowns in t h is phase o f th e stu d y c o n s is te d
o f th e im m ediate basal p o r t io n , th e culm , and a p p ro x im a te ly 8 cm o f
th e r o o ts .
FIGURE 2.
Caged n e e d !e -a n d -th re a d p la n t
21
P la n t and G rasshopper Growth Curves
On th e stu d y s i t e near Three F o rk s , Montana, f o u r g la s s panes
were b u rie d on May 2 , 1975.
The panes were a d ju s te d a t a s l i g h t
a n g le in a bank o f th e sm all f lo w - in area which runs th ro u g h the
e x c lo s u re .
Two panes had s if t e d s o i l p laced a g a in s t th e g la s s .
One
was p la n te d w ith one w e ste rn w heatgrass p la n t and th e o th e r w ith one
n e e d !e -a n d -th re a d p la n t .
The t h i r d g la s s pane was p la ce d under a
n a t u r a lly o c c u r r in g w e ste rn w heatgrass p la n t and th e f o u r th under
a n e e d !e -a n d -th re a d p la n t .
Some o f th e o ld e r p a rts o f th e r o o t
system o f th e se l a t t e r grasses were c u t away to accommodate the
g la s s .
The range and mean o f th e maximum h e ig h t o f le a ve s held
v e r t i c a l l y , le a f s ta g e , a p ic a l m eriste m lo c a t io n , r o o t g ro w th , and
phenology were re co rd e d b i-w e e k ly from May to September f o r th e two
grass sp e cie s s tu d ie d .
Weekly c lim a t ic d ata were a ls o re c o rd e d .
S o il m o is tu re was
ta b u la te d u s in g a gypsum b lo c k w h ich was placed 20 cm below th e
s u rfa c e in one o f th e b u rie d g la s s panes.
G rasshoppers were c o lle c te d w ith a sweep n e t each week from
th e same sa m pling a re a .
They were s to re d in a fr e e z e r and l a t e r
i d e n t i f i e d and ta b u la te d in t o developm ental sta g e s .
RESULTS AND DISCUSSION '
N e edle-and-Thread D e fo lia tio n
Greenhouse
The two d e f o lia t io n tre a tm e n ts o f th e o ld e r group o f n e e d le a n d -th re a d p la n ts s tu d ie d in th e greenhouse had 48 days o f grassho pper
g ra z in g .
T h is r e s u lte d in a p p ro x im a te ly 50 and 70 p e rc e n t removal
by w e ig h t o f th e to p grow th w hich a re r e fe r r e d to as moderate and
heavy g ra z in g r e s p e c t iv e ly (F ig u re 3 ) .
The oven d ry w e ig h ts o f to p
grow th a re g iv e n in T able 3 a lo n g w ith th e a n a ly s is o f v a ria n c e .
The r o o t grow th in response to both g ra z in g tre a tm e n ts was
reduced a p p ro x im a te ly 50 p e rc e n t as compared to th e un-grazed p la n ts
( F ig u re 3 ).
However, an a n a ly s is o f v a ria n c e o f r o o t w e ig h t (T a b le 4)
in d ic a te d th e re were no s i g n i f i c a n t d iffe r e n c e s among th e tre a tm e n ts
a t th e f i v e p e rc e n t le v e l.
The crown w e ig h t re p re s e n te d by th e crown and e ig h t cm o f o ld
ro o ts d id n o t show any s ig n i f i c a n t tre a tm e n t e f f e c t (T a b le 5 ).
T h is
was p ro b a b ly due to th e unequal s iz e o f the p la n ts s e le c te d in th e
f ie ld .
The average crown w e ig h t o f th e h e a v ily grazed p la n ts was
n e a rly tw ic e as much as t h a t o f e it h e r th e m oderate o r the un-grazed
p la n ts .
T his may be re s p o n s ib le f o r much o f th e v a r ia t io n
r o o t w e ig h t s .
in th e
The d e f o lia t io n
o f th e green -up phase o f t h is
stu d y
suggested t h a t any grasshopper g ra z in g o f one week (new grow th)
o f n e e d le -a n d -th re a d p la n ts was co n s id e re d to o d e t r im e n t a l.
.... g
grazed p la n ts in t h is s tu d y d ie d back w it h in a few days due to th e
grassho pper d e f o l ia t io n .
■iI
Al I
The method by w hich th e p la n t r o o t system
was c o lle c te d in th e f i e l d
s tre s s on th e se p la n ts .
is
th o u g h t to cause a g r e a t amount o f
The r o o t system was to o weak to a llo w any
d e f o lia t io n a t t h is sta g e o f developm ent.
2
4
2.0
un - g r a z e d
1.8
TOP WEIGHT
a
1.6
1 .4
1.2
Moderate
g ra z in g
1.0
0 .8
0.6
0.4
b
Heavy
g ra z in g
C
0.2
0
0.2
0.4
0.6
0. 8
X
X
1.0
1.2
1 .4
1.6
ROOT WEIGHT
X
1.8
2.0
FIGURE 3.
Top and r o o t w e ig h ts o f n e e d le -a n d -th re a d grass f o l l o w i n g
48 days o f grasshopper d e f o l i a t i o n .
Bars having the same
lo w er case l e t t e r s are n o t s i g n i f i c a n t l y d i f f e r e n t a t th e
.05 le v e l using Duncan's new m u l t i p l e range t e s t
(greenhouse d a ta )
TABLE 3.
Dry w e ig h ts ( g m /p la n t) o f n e e d le -a n d -th r e a d to p growth
rem a ining a f t e r 48 days o f grasshopper d e f o l i a t i o n
(g re e n h o u s e ).
TREATMENT
I
2
REPLICATE
3
4
TOTAL
MEAN
Heavy g r a z in g
0.605
0.480 '
0.465
0.476
2.0 2 6
0.506
Moderate g r a z in g
0.898
0.977
0.826
0 .8 2 6
3.527
0.881
Un-grazed
1.829
1.414
1.746
1.904
6 .8 9 3
1.723
.
ANALYSIS OF VARIANCE
SOURCE
TOTAL
REPS
TREATMENTS.
ERROR
DF
SS
3.275
4.031E-02
. 3.106
.128
11
3
2
6
MS
1 .553
2.138E
F=72.6 2 2 * * 1 /
TREATMENT
Un-grazed
Moderate g ra z in g
Heavy g r a z in g
MEAN'
I . 7 2 3 a -/
0.881b
0.506c
I/
H ig h ly s i g n i f i c a n t (P .01)
2/
Means havin g th e same lo w er case l e t t e r s are n o t s i g n i f i c a n t l y
d i f f e r e n t a t the .05 le v e l u sin g Duncan's new m u l t i p l e range
te s t.
I
26
table
4,
Dry w e ig h ts ( g m / p la n t ) o f n e e d !e -a n d -th re a d r o o t growth
i n response t o grasshopper d e f o l i a t i o n
TREATMENT
2
Heavy g r a z in g
1.314
1.083
Moderate g r a z in g
0 .6 8 8
Un-grazed
2.091
£
I
REPLICATE
3
I
(gre enho use).
4
TOTAL
0.382
0.509
3 .2 8 8
0 .8 2 2
0.500
1.543
0 .8 3 3
3.564
0.8 9 1
1.170
1.646
1.560
6.467
1.616
ANALYSIS OF VARIANCE
1I
I I
■
I'
'I-
II
SOURCE
TOTAL
REPS
TREATMENTS
ERROR
F = 3 .6 7 ll/
I/
Not s i g n i f i c a n t (P .05)
DF
11
3
2
6
SS
3.204
.385
1.551
1.267
MS
.775
.211
MEAN
27
TABLE 5.
Dry w e ig h ts ( g m / p la n t ) o f n e e d le -a n d -th re a d
crown (base
Plus 7 .5 cm o l d r o o t s ) growth as r e la t e d to
grasshopper
d e fo lia tio n
TREATMENT
Heavy g r a z in g
Moderate g r a z in g
Un-grazed
(gre enho use).
]
16A92
4.7 9 9
6.329
repli cate
2
3
4
TOTAL
MEAN
10.088
8 .6 3 4
6 .3 9 3
A l . 607
6.5 7 6
10.401
5.510
6.422
7 .2 6 3
23.307
5 .3 2 5
5.8 2 6
6 .1 3 0
■25.047
6.261
ANA LYSIS OF VARIANCE
SOURCE
TOTAL
REPS
TREATMENTS
ERROR
F= 3 . 5 0 & V
I/
Not s i g n i f i c a n t (P .05)
DF
11
3
2
6
SS
111.371
16.692
51.013
43.667
MS
25.506
7.2 7 8
The tr e a tm e n t p e r io d f o r th e f i e l d
grass ended August
grassho ppers.
t r e a t e d cages.
6
study w i t h n e e d le -a n d -th re a d
, 1974, 48 days a f t e r th e i n i t i a l
in fe s ta tio n w ith
By t h i s tim e no .grasshoppers remained a l i v e w i t h i n th e
The d e f o l i a t i o n p e r io d o ccurred between th e emergence
o f in f l o r e s c e n c e and seed s h a t t e r a t which tim e th e grasshoppers
removed 83 and
88
p e rc e n t ( w e ig h t e s tim a te ) o f th e to p growth o f
th e p re -e x c a v a te d and non-excavated p la n t s r e s p e c t i v e l y ( F ig u re 4 ) .
Dry w e ig h ts o f th e re m a in in g to p grow th are g ive n i n Table
6
along
w i t h th e a n a ly s is o f v a r ia n c e .
The response o f th e r o o t growth to t h i s d e f o l i a t i o n i s a ls o
shown in F ig u re 4.
N e e d le -a n d -th re a d r o o ts o f th e grazed p re ­
excavated p la n t s were 63 p e rc e n t le s s by w e ig h t than th e un-grazed
p re -e x c a v a te d p l a n t s .
The r o o t s o f th e non-excavated p la n t s were
reduced 38 p e rc e n t by g r a z in g .
T h is r e d u c t io n i n r o o t growth is
s i g n i f i c a n t a t th e f i v e p e rc e n t le v e l
(T a b le 7 ) .
The d i f f e r e n c e between p e r c e n t r o o t r e d u c t io n o f th e p re excavated and non-excavated p la n t s i s p ro b a b ly due t o e x c a v a tin g
the p la n t s b e fo r e th e g r a z in g p e r io d .
The r o o t system under the
non-excavated p la n t s would in c lu d e both o ld and new a c t i v e r o o t s .
The r o o ts o f th e excavated p la n t s would in c lu d e p r i m a r i l y the
newer a c t i v e r o o t s .
However, th e r o o t s o f the p re -e x c a v a te d un-grazed
p la n t s were g r e a t e r i n w e ig h t than those o f the non-excavated
2
9
un-grazed p l a n t s .
The sam pling method employed c o u ld acco u n t f o r
much o f t h e v a r i a t i o n s found here.
Table
8
i n d ic a t e s t h a t crown w e ig h ts were n o t s i g n i f i c a n t l y
a f f e c t e d by grasshopper d e f o l i a t i o n .
As p r e v i o u s l y . i n d i c a t e d .
in th e greenhouse s t u d y , crown w e ig h t d i f f e r e n c e s were p ro b a b ly
due t o s e l e c t i n g unequal s i z e p l a n t s .
3
0
FI,ANTS
fliTF-EXCAVATED
FLANTS
NOT EXCAVATED
u n -qrazed
2.0
1.8
TOP WEIGHT
1.6
un-g ra ze d
1.4
1.2
Ic
2
1.0
0
0 .8
0.6
0 .4
grazed
g ra z e d
0.2
0
0.2
0 .4
0.6
0 .8
1 .0
1.2
1 .4
1.6
1
1.8
"
2.0
2.2
ROOT WEIGHT
2 .4
2.6
2.8
3.0
FIGURE 4.
Top and r o o t w e ig h ts o f n e e d le -a n d -th re a d f o l l o w i n g a p p r o x i­
m a te ly 40 days o f grasshopper d e f o l i a t i o n ( f i e l d d a ta )
I
f
31
I
TABLE
6
.
Weights ( g m /p la n t) o f n e e d le -a n d -th re a d to p growth
re m a in in g a f t e r a p p ro x im a te ly 40 days o f grasshopper
d e fo lia tio n
( fie ld d a ta ).
PLANTS NOT EXCAVATED
TREATMENT
I
Un-grazed
Grazed
I
REPLICATE
3
2
1.713
0.279
2.818
0.246
1.698
0.3 5 6
4
3.570
0.434
5 .
TOTAL
MEAN
2.3 6 0
12.159
2.431
0.105
1 .4 2 0
0.2 8 4
ANALYSIS OF VARIANCE
MS
SS
14.098
1.403
11.533
1.163
DF
9
4
I
4
SOURCE
TOTAL
REPS
TREATMENTS
ERROR
11.533
.291
F =39.6 5 1 **1 /
PLANTS PRE- EXCAVATED
TREATMENT
Un-grazed
Grazed
I
1.085
0.182
REPLICATE
3
2
1 .5 5 8
0.455
1.420
'0 . 1 6 2
4
1.404
0.376
5
1.544
0.010
TOTAL
MEAN
7.011
1.185
1.402
0.237
ANALYSIS OF VARIANCE
SOURCE
TOTAL
REPS
TREATMENTS
ERROR
DF
9
4
I
4
F-115 . 0 2 6 * * - /
I/
H ig h ly s i g n i f i c a n t (P . 0 1 )
SS
3.667
.154
3.394
.118
MS
3 .3 9 4
2 .9 5 1 E- 0 2
TABLE 7.
Weights ( g m / p la n t ) o f n e e d ]e -a n d -th re a d r o o t s i n response
t o grassho pper d e f o l i a t i o n
( f i e l d d a ta ) .
PLANTS NOT EXCAVATED
TREATMENT
Un-grazed
Grazed
I
1.950
1.388
REPLICATE
3
2
2.035
1.953
2.904
2.008
4
3.562
1.471
5
2.493
1.155
TOTAL
12.944
7.975
MEAN
2.588
!.'595
ANALYSIS OF VARIANCE
SOURCE
TOTAL
REPS
TREATMENTS
ERROR
DF
9
4
I
4
SS
MS
4.790
1.146
2.469
1.175
2.469
.294
F=8.4 0 6 *1 /
PLANTS PRE-EXCAVATED
TREATMENT
I
Un-grazed
Grazed
3.568
1.158
REPLICATE
3
2
3 221
I 055
3 .6 1 3
1.149
4
2 .8 2 5
0 .9 9 6
5
TOTAL
MEAN
380
14.607
018
5.376
2.921
1 .0 7 5
ANALYSIS OF VARIANCE
SOURCE
TOTAL
REPS
TREATMENTS
ERROR
F=22.685*l/
I/
S i g n i f i c a n t (P .05)
DF
9
4
I
4
SS
11.915
MS
1.891
8.521
8.521
1.5 0 2
.376
9rassh0 pPer d e fo liatio n ( f ie ld data).
P L A N T S NOT EXCAVATED
treatment
I
Un-grazed
Grazed
a n a l y s is
10^830
8 .7 2 5
of
r e p l ic a t e
2
3
8.5 3 6
14.447
6.780
7.140
.
4
15.905
11.200
5
24.200
3.523
TOTAL .
'3 .9 1 8
!7.368
MEAN
14.783
7.473
VARIANCE'
source
total
DF
SS
9
4
REPS
treatments
error
MS
309.945
52.526
I
1 33.590
4
133.590
30.957
123.829
F = 4 '3 1 5 -/
pLA^TS PRE-EXCAVATED
TREATMENT
]
G - I d zed
ANALYSIS
of
REPLICATE
3
2
11.745
10.073
i; “ °
13.105
3 .80 5
VARIANCE
SOURCE
TOTAL
REPS
TREATMENTS
ERROR
DF
9
4
I
4
F = .3 7 D l/
I/
4
Not significant (p .05)
I
SS
114.475
64.477
4 .2 3 8
■ 45.760
5
9 .0 3 5
9 .1 8 5
total
MEAN
53.600
47.090
1 0 .7 2 0
9.41 8
MS
4 .2 3 8
11.440
3
4
Western Wheatgrass D e f o l i a t i o n
Greenhouse
In th e t h r e e g r a z in g tre a tm e n ts s t u d i e d , w e stern wheatgrass
s e e d lin g s were s u b je c te d t o g rassho pper d e f o l i a t i o n .
The grasshoppers
removed 20, 50, and 80 p e r c e n t ( o c u l a r e s t im a t e ) o f th e to p growth
as compared t o th e u n -grazed p l a n t s .
These g r a z in g tre a tm e n ts are
r e f e r r e d t o as l i g h t , m oderate, and heavy g r a z in g r e s p e c t i v e l y .
The c l i p p i n g t r e a tm e n t o c c u rre d o n ly on day 31, a t w hich tim e
90 p e r c e n t ( o c u l a r e s t im a t e ) o f th e to p growth was removed.
The to p re g ro w th response o f w e s te rn wheatgrass t o d e f o l i a t i o n
is
i l l u s t r a t e d by th e b a r graph i n F ig u r e 5.
The w e ig h t data were
take n 46 days a f t e r th e end o f th e t r e a tm e n t p e r io d .
to p w e ig h ts and s t a t i s t i c a l
The o ve n -d ry
t e s t s a re g iv e n in Table 9.
No s i g n i f i c a n t
d i f f e r e n c e i n to p grow th e x i s t e d between th e l i g h t g r a z in g and c l i p p i n g ,
I
between th e c l i p p i n g and moderate g r a z in g , and between th e c o n t r o l
and l i g h t g r a z in g .
The heavy g r a z in g d i f f e r e d s i g n i f i c a n t l y from
a l l o th e r tre a tm e n ts .
The r o o t w e ig h t responses to a l l
i n F ig u re 5.
d iffe re n c e s
f i v e tre a tm e n ts a r e i l l u s t r a t e d
The d ata g iv e n in T ab le 10 show t h e r e were no s i g n i f i c a n t
i n r o o t w e ig h ts between th e l i g h t g r a z in g and u n -g ra z e d ,
and between th e c l i p p i n g and moderate g r a z in g .
The r o o t s o f the
c l i p p i n g and m o d e ra te ly grazed p la n t s were reduced 60 and 70 p e rc e n t
re s p e c tiv e ly .
The r o o t s o f th e h e a v i l y grazed p la n t s were reduced
3
5
85 p e r c e n t compared t o th o s e o f th e u n -g ra ze d p l a n t s .
The o v e n -d ry
w e ig h ts a re g iv e n i n T a b le 10 a lo n g w i t h th e a n a ly s is o f v a r ia n c e
and Duncan's new m u l t i p l e range t e s t .
These data i n d i c a t e t h a t grassh o p p e r d e f o l i a t i o n o f young
a c t i v e l y grow ing w e s te rn wheatgrass p l a n t s i n th e greenhouse a t
moderate and heavy g r a z in g i n t e n s i t i e s w i l l
s i g n i f i c a n t l y reduce
th e mass o f r o o t s produced, even a f t e r 46 days o f r e s t f o l l o w i n g
t r e a tm e n t .
The c l i p p i n g and moderate g r a z in g tre a tm e n ts i n t h i s
e x p e rim e n t responded s i m i l a r l y .
The l i g h t g r a z in g t r e a tm e n t had
no s i g n i f i c a n t e f f e c t on r o o t grow th.
.-
ay
^ f i nn f Sii Y ^ ^ i Z - . ' ^ : 1A ^ . . _,
36
1.0
0 .9
TOP WEIGHT
0 .8
un-grazed
IJ Kht
0 .7
grazing
0.6
a
b
2 0 .5
Moderate
clipping
grazing
"0 .4
c
0 .3
0.2
a
Heavy
grazing
0.1
d
0
0.1
c
0.2
0 .3
0 .4
0 .5
b
I
0.6
0 .7
gO.8
Z
crO1O
ROOT WEIGHT
1.0
1.1
1.2
1 .3
1 .4
FIGURE 5.
Top and r o o t w e ig h ts o f w e s te rn wheatgrass i n r e l a t i o n s h i p
t o c l i p p i n g and grassh o p p e r d e f o l i a t i o n .
Bars having the
same lo w e r case l e t t e r s a re n o t s i g n i f i c a n t l y d i f f e r e n t
a t th e .05 le v e l u s in g Duncan's new m u l t i p l e range t e s t .
f
TABLE 9.
Weights ( gm/4 p l a n t s ) o f w e ste rn wheatgrass to p grow th
as r e l a t e d t o grassh o p p e r d e f o l i a t i o n and c l i p p i n g
TREATMENT
C l ip p in g
Heavy g r a z in g
Moderate g r a z in g
L i g h t g r a z in g
Un-grazed
I
2
0. 769
0.435
0.115
0.427
0.153
0.632
0.708
0.810 . 0.720
0.110
REPLICATE
. 3
4
0.335
0.203
0.573
0.433
0.517
0.272
0.133
0.354
0.584
0.700
5
TOTAL
MEAN
0.391
0.104
0.330
0.687
0.999
2.203
0.667
1.838
3.045
3.748
0.440
0.133
0.367
0.609
0.749
ANALYSIS OF VARIANCE
SOURCE '
TOTAL
REPS
TREATMENTS
ERROR
DF
24
4
4
16
SS
1.530
7 . 967E-02
1.108
.342
MS
277
: . 2 . I 36E-02
F = 1 2 .9 7 3 * * ^ /
TREATMENT
Un-grazed
L i g h t g r a z in g
C l ip p in g
Moderate g r a z in g
Heavy g r a z in g
MEAN
0 .7 4 9 a -/
0 . 609ab
0.440bc
0.367c
0.133d
I
V
H ig h ly s i g n i f i c a n t ( P ' . O l )
2/
Means h a v in g th e same lo w e r case l e t t e r s are n o t s i g n i f i c a n t l y
d i f f e r e n t a t th e .05 le v e l u s in g Duncan's new m u l t i p l e range
te s t.
I
3
8
TABLE 10.
W eights (gm/4 p l a n t s ) o f w e s te rn wheatgrass r o o t s i n
response t o g ra s s h o p p e r d e f o l i a t i o n and c l i p p i n g .
C lip p in g
Heavy g r a z in g
Moderate g r a z in g
L i g h t g r a z in g
Un-grazed
REPLICATE
3
I
2
0.979
0.315
0.762
1.280
1.877
0.567
0.149
0.184
1.298
1.169
TREATMENT
0.415
0.286
1.184
0.924
1.280
4
5
TOTAL
MEAN
0.280
0.130
0.298
0.965
0.704
0.519
0.173
0.542
1.113
1.883
2.760
1.053
2.970
5.580
6.913
0.552
0.210
0.594
1.116
1.382
ANALYSIS OF VARIANCE
SOURCE
TOTAL
REPS
TREATMENTS
ERROR
DF
24
4
4
16
~
MS
SS
6.502
.892
4.432
1.178
1.108
7 . 365E-02
F = I5 . 0 4 7 * * - /
TREATMENT
Un-grazed
L i g h t g r a z in g
Moderate g r a z in g
C l ip p in g ■
Heavy g r a z in g
MEAN
I . 382a-/
I . 116a .
0 . 594b
0 . 551bc
0 . 210c
I
V
H ig h ly s i g n i f i c a n t (P .0 1 )
2/
Means h a vin g th e same lo w e r case l e t t e r s a re n o t s i g n i f i c a n t l y
d i f f e r e n t a t th e .05 le v e l u s in g Duncan's new m u l t i p l e range
te s t.
r
39
The crown and rhizom e w e ig h t d ata a re pre se n te d i n F ig u r e
These data i n d i c a t e
6.
t h a t a lth o u g h th e r e was no s i g n i f i c a n t d i f f e r e n c e
i n th e crown w e ig h ts between th e l i g h t g r a z in g and th e un-grazed
t r e a t m e n t s , b oth th e one tim e c l i p p i n g and moderate g r a z in g i n t e n s i t i e s
s i g n i f i c a n t l y reduced crown w e ig h ts by 49 p e r c e n t.
tr e a tm e n t reduced crown w e ig h t by 80 p e r c e n t.
and s t a t i s t i c a l
The heavy g r a z in g
The crown w e ig h ts
t e s t s a re g iv e n i n T a b le 11.
Both th e heavy and moderate g r a z in g i n t e n s i t i e s s i g n i f i c a n t l y
reduced rhizome w e ig h ts ( a p p r o x im a t e ly 90 and 100 p e r c e n t r e s p e c t i v e l y )
from tho se o f th e u n -grazed p l a n t s .
However, these t re a tm e n ts were
n o t s i g n i f i c a n t l y d i f f e r e n t fro m th e l i g h t g r a z in g o r c l i p p i n g
tr e a tm e n ts (T a b le 1 2 ).
There were no s i g n i f i c a n t d i f f e r e n c e s . in
rhizom e w e ig h ts between th e u n -g ra z e d , th e l i g h t l y g ra ze d , and th e
c l i p p i n g tr e a tm e n t s .
i-
4
0
CROWN WEIGHT
un-grazed
Moderate
grazing
c lip p in g
Heavy
grazing
RHIZOME WEIGHT
FIGURE
jlmi.I* ^ii it
6.
Crown and rhizom e w e ig h t response o f w e ste rn wheatgrass
t o c l i p p i n g and gras sh o p p e r d e f o l i a t i o n .
Bars having
th e same lo w e r case l e t t e r s a re n o t s i g n i f i c a n t l y d i f f e r e n t
a t th e .05 le v e l u sin g Duncan's new m u l t i p l e range t e s t .
I
* W1'.f lIlI11^ r
.111jiyrT~r'r“trr
4
1
TABLE 11.
W eights (gm/4 p l a n t s ) o f w e s te rn w heatgrass crowns i n
response t o g ra ssho pper d e f o l i a t i o n and c l i p p i n g .
C l ip p in g
Heavy g r a z in g
Moderate g r a z in g
L i g h t g r a z in g
Un-grazed
REPLICATE
3
.4
I
2
0.0 4 8
0.039
0.014
0.015
0.070
0.073
TREATMENT
0.010
0.056
0.047
0.075
0.040
0.022
0.059
0.062
0.059
0.024
0.013
0.029
O’. 056
0.073
5
TOTAL
MEAN
0.034
0.185
0.071
0.189
0.299
0.362
0.037
0.014
0.037
0.059
0.072
0.012
0.030
0.064
0.082
ANALYSIS OF VARIANCE
SOURCE
TOTAL
REPS
TREATMENTS
ERROR
SS
I . 258E-02
2.886E -04
1.016E-02
2.131E-02
DF
24
4
4
16
F = 1 9 .0 6 5 * * - /
TREATMENT .
Un-grazed
L i g h t g r a z in g
Moderate g r a z in g
C l ip p in g
Heavy g r a z in g
MS
2
. 539E-03
I . 332E-04
-
MEAN
0 .0 7 2 a -/
0.059a
0.037b
0.037b
0.014c
I
V
H ig h ly s i g n i f i c a n t (P .01)
2/
Means h a v in g th e same lo w e r case l e t t e r s are n o t s i g n i f i c a n t l y
d i f f e r e n t a t th e .05 le v e l u s in g Duncan's new m u l t i p l e range
te s t.
42
TABLE 12.
Weights (gm/4 p l a n t s ) o f w e s te rn w heatgrass rhizom es in
response to. g ra ssh o p p e r d e f o l i a t i o n and c l i p p i n g .
C lip p in g
Heavy g r a z in g
Moderate g r a z in g
L i g h t g r a z in g
Un-grazed
REPLICATE
3
4
5
TOTAL
MEAN
0.001
0.0 0 0
0.000
0.025
0.079
0.015
0.0 0 2
0.000
0.000
0.000
0.002
0.000
0.012
0.000
0.017
0.014
0.005
0.042
0.016
0.071
0.132
0.003
0 .0 1 4
0.026
I
2
0.019
0.000
0.033
0.0 0 0
0.000
0.000
0.021
TREATMENT
0.016
0.014
0.036
0.038
ANALYSIS OF VARIANCE
SOURCE
TOTAL
REPS
TREATMENTS
ERROR
SS
4 . 773E-03
3 . 555E-04
2.191E-03
2 . 227E-03
DF
24
4
' 4
.
16 '
MS
5.477E-04
1.392E-04
F = 3 .9 3 5 * - /
TREATMENT
Un-grazed
C lip p in g
L i g h t g r a z in g
Moderate g r a z in g
Heavy g r a z in g
MEAN
0.026a
0. OlSab
0.014ab
0.003b
0 .000b
I/
S i g n i f i c a n t (P .0 5 )
Zj
Means h a v in g th e same lo w e r case l e t t e r s are n o t s i g n i f i c a n t l y
d i f f e r e n t a t th e .05 le v e l u s in g Duncan's new m u l t i p l e range
te s t.
43
The t o t a l
depth o f p e n e t r a t io n s o f th e a c t i v e l y grow ing r o o ts
on day 64 a re i l l u s t r a t e d
by th e b a r graph i n F ig u re 7.
Data were
re co rd e d on t h i s day because by t h i s tim e some o f th e r o o t s had
reached th e bottom o f th e b o x . . The c l i p p i n g and m oderate g ra z in g
responded s i m i l a r l y w i t h a r e d u c t io n in depth r o o t p e n e t r a t io n
o f 26 and 22 p e r c e n t r e s p e c t i v e l y .
No s i g n i f i c a n t d i f f e r e n c e o c c u rre d
between th e l i g h t g r a z in g and th e un-grazed t r e a tm e n t s .
The heavy
grazed t r e a tm e n t reduced th e le n g t h o f r o o t p e n e t r a t io n by 49 p e rc e n t
when compared t o th e un-grazed p l a n t s .
Table 13 l i s t s
th e r o o t
le n g t h i n c e n t im e t e r s o f th e f i v e t re a tm e n ts and th e s t a t i s t i c a l
te s t.
44
Heavy
graz i n g
FIGURE 7.
Maximum r o o t depth response o f w e stern wheatgrass to
g ra ssho pper d e f o l i a t i o n and c l i p p i n g .
Bars having the
same lo w e r case l e t t e r s a re n o t s i g n i f i c a n t l y d i f f e r e n t
a t th e .05 le v e l u sin g Duncan's new m u l t i p l e range t e s t .
45
TABLE 13.
Maximum dep th o f p e n e t r a t io n (cm) o f w e s te rn wheatgrass
r o o t s i n response t o grassh o p p e r d e f o l i a t i o n and c l i p p i n g .
I
TREATMENT
C l ip p in g
Heavy g r a z in g
Moderate g r a z in g
L i g h t g r a z in g
Un-grazed
2
52.8
2 4.6
4 7.5
58.0
54.1
REPLICATE
3
34.3
25.3
37.7
3 7.8
50.0
54.3
5 1 .5
55.6
5 8.0
28.3
.
4
36.0
30.2
32.1
49.9
4 7 .4
5
3 8 .7
30.1
' 4 2.9
56.0
5 8 .0
TOTAL
MEAN
199.5
138.5
210.3
273.8
39.90
27.70
42.06
54.76
53.80
269.0
ANALYSIS OF VARIANCE
SOURCE
TOTAL
REPS
TREATMENTS
ERROR
DF
24
4
4
16
SS
3063.122
197.050
2487.238
378.834
MS
621.809
23.677
F -2 6 .2 6 2 **-/
TREATMENT
L i g h t g r a z in g
Un-grazed
Moderate g r a z in g
C lip p in g
Heavy c l i p p i n g
MEAN
5 4 . 76d
53.80a
42.06b
39.90b
27.70c
I/
H ig h ly s i g n i f i c a n t (P .0 1 )
2/
Means h a ving th e same lo w e r case l e t t e r s are n o t s i g n i f i c a n t l y
d i f f e r e n t a t th e .05 le v e l u s in g Duncan's new m u l t i p l e range
te s t.
4
6
The r a t e o f r o o t grow th o f a l l
f i v e tre a tm e n ts from day 28
th ro u g h day 55 i s re p re s e n te d i n F ig u re
8
.
The g r a z in g tr e a tm e n t
p e r io d o c c u rre d from day 31 th ro u g h day 47.
The c l i p p i n g t r e a tm e n t stopped a l l
r o o t growth f o r a p e r io d o f
f i v e days d u r in g w hich tim e t h e r e was an in c re a s e i n r a t e o f to p
grow th o f th e c li p p e d p l a n t s when compared t o th e u n -grazed p la n t s
( F ig u r e 9 ) .
By th e end o f th e t e s t i n g p e r io d th e average h e i g h t
o f th e c li p p e d and th e u n -g ra ze d p l a n t s was e q u a l.
The g r a z in g tre a tm e n ts d i d n o t have th e im mediate e f f e c t t h a t
o c c u rre d i n th e c l i p p i n g t r e a t m e n t , b u t as th e d e f o l i a t i o n i n t e n s i t y
in c re a s e d w i t h tim e and th e grassho ppers in c re a s e d i n s i z e , th e d a i l y
r o o t e l o n g a t i o n g r a d u a l l y decrea sed.
The heavy g r a z in g tr e a tm e n t
on day 42 n e a r ly stopped any f u r t h e r r o o t e lo n g a t io n d u r in g th e tim e
measured.
I t was f e l t t h a t i f
heavy g r a z in g had been c o n tin u e d the
I
w e s te rn wheatgrass p l a n t s would have d ie d .
As p r e v i o u s l y in d i c a t e d by r o o t w e ig h ts a t th e end o f t h i s s tu d y
p e r io d and th e r a t e o f r o o t g r o w th , th e un-grazed and l i g h t l y grazed
p la n t s responded s i m i l a r l y .
The m oderate g r a z in g and c l i p p i n g
tr e a tm e n ts were n e a r ly on th e same i n c l i n e o f r a t e o f r o o t e lo n g a tio n
( F ig u r e
8
).
The d ata showed r o o t s o f th e h e a v il y grazed p l a n t s were
a f f e c t e d most d e t r i m e n t a l l y .
7 rea*-er.t P e r i o d
28
FIGURE
8
29
.
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
Root grow th r a t e o f w e s te rn wheatgrass i n response t o grasshopper d e f o l i a t i o n
and c l i p p i n g .
6C
treatment
period
60
FIGURE 9.
65
70
75
80
Top growth response o f w e stern wheatgrass t o c l i p p i n g .
65
49
The numbers o f new shoo ts produced by w e ste rn w heatgrass in
response t o f o u r o f th e f i v e - t r e a t m e n t s i s shown i n F ig u r e 10.
The
heavy g r a z in g tr e a tm e n ts i s n o t re p re s e n te d because no new shoots
were produced.
There was no s i g n i f i c a n t d i f f e r e n c e between th e
u n -g ra z e d , l i g h t l y
g ra z e d , and c l i p p i n g tre a tm e n ts ( T a b le 1 4 ).
However, th e m o d e ra te ly grazed p l a n t s had s i g n i f i c a n t l y 35 p e r c e n t
fe w e r new sho o ts than th e u n -g ra ze d p l a n t s .
50
64
66
68
70
72
74
76
78
80
82
84
86
88
90
92
94
DAY
FIGURE 10.
The t o t a l new shoots produced by w e stern wheatgrass in
response t o c l i p p i n g and grassho pper d e f o l i a t i o n .
Lines
having th e same lo w e r case l e t t e r s are n o t s i g n i f i c a n t l y
d i f f e r e n t a t th e .05 l e v e l u s in g Duncan's new m u l t i p l e
range t e s t .
5
1
TABLE 14.
Number o f new s h o o ts produced by w e s te rn wheatgrass i n
response t o g ra ssh o p p e r d e f o l i a t i o n and c l i p p i n g .
TREATMENT
C l ip p in g
Heavy g r a z in g
Moderate g r a z in g
L i g h t g r a z in g
Un-grazed
I
REPLICATE
.3
I
2
8
0
3
4
2
0
0
0
0
2
12
8
0
0
9
I0
I0
0
13
10
4
5
.
TOTAL
7
34
0
2
0
22
11
15
55
52
MEAN
6.8
0.0
4 .4
11 .0
1 0.4
ANALYSIS OF VARIANCE
SOURCE
TOTAL .
REPS
TREATMENTS
ERROR
DF
24
4
4
16
SS
694.24
73.84
411.04
209.36
MS
102.75
13.085
F= 7 . 8 5 3 * * - /
TREATMENT
L i g h t g r a z in g
Un-grazed
C l ip p in g
Moderate g r a z in g
Heavy g r a z in g
MEAN
11.0a
.
I
.
10.4a
6 . 8 ab
4 .4 b c
0 .0c
"
I/
H i g h l y s i g n i f i c a n t (P .0 5 )
2/
Means h a v in g th e same lo w e r case l e t t e r s are n o t s i g n i f i c a n t l y
d i f f e r e n t a t th e .05 le v e l u s in g Duncan's new m u l t i p l e range t e s t .
V--
52
P la n t and G rasshopper Development i n th e F i e ld
The h e i g h t o f th e culm development i s expressed g r a p h i c a l l y f o r
w e s te rn w h eatgrass and n e e d !e -a n d - th r e a d grass in F ig u re s 11 and 12
r e s p e c tiv e ly .
The range and mean are g iv e n f o r each week sampled.
Al so in d i c a t e d on th e se f i g u r e s a r e th e gen e ra l developm ental curves
o f th e grassho ppers c o l l e c t e d a t th e s i t e .
11
and
12,
As in d ic a t e d i n F ig u re s
th e development p e r io d f o r th e l a t e r i n s t a r s and a d u l t
sta g e o f th e grasshoppers c o l l e c t e d on th e s i t e o c c u rre d a f t e r th e
a c t i v e grow th p e r io d f o r th e two cool season grass sp e cie s s t u d ie d .
T a b le 15 l i s t s
some o f th e grassh o p p e r species c o l l e c t e d and t h e i r
r e s p e c t iv e deve lop m en tal p e r io d .
grassho ppers l i f e
September.
Most o f th e a d u l t p o r t i o n o f th e
span o c c u rre d d u r in g t h e l a t t e r p a r t o f J u l y th ro u g h
An e x c e p tio n t o t h i s
w i n t e r s i n th e nympha l s ta g e .
i s Psoloessa d e l i c a t u l a w hich o v e r ­
T h is g ra ssh o p p e r c o u ld p o s s i b l y graze
p l a n t p a r t s d u r in g th e a c t i v e grow ing season o f cool season g ra sse s.
However, from p e rso n a l o b s e r v a tio n s t h i s grasshopper does n o t u s u a ll y
o c c u r i n r e l a t i v e l y h ig h numbers.
I t was observed t h a t th e y e a r under c o n s i d e r a t io n was a t y p i c a l .
The s p r in g o f 1975 was u n u s u a lly cool w i t h h ig h p r e c i p i t a t i o n
page 1 1 ).
(T a b le I ,
The e f f e c t o f t h i s w e ath er d i f f e r e n c e on g ra ssho pper
development i s unknown.
O-
Adult-
36
-o
Grasshopper Development
34
32
O
30
I
range
28
26
§ 24
I 22
S
3
20
CJ
3 tb -
. 18
8
16
Ol
LO
14
12
10
8
k
k
23
30
6
t
st
O -----------I5
instar------- O
4
2
0
9
16
MAY
I
FIGURE T l .
6
'
13
JUNE
20
30
7
14
JULY
21
28
I
8
15
AOGUST
22
SEPTEMBER
Average and range o f culm h e ig h t f o r w e stern wheatgrass as r e la t e d
t o grassho pper development.
32
20
o
26
-o
jrassi.cpjer ievelopcen*.
26
24
_•
“
■5 20
I
18
16
§14
12
U l
10
8
6
4
2
0
2
9
16
HAY
FIGURE 12.
23
6
13
JUNE
20
30
7
14
JULY
21
28
I
8
15
AUGUST
22
5
SEPTEMBER
Average and range o f culm h e ig h t f o r n e e d le -a n d -th re a d as r e la t e d
t o grassho pper development.
TABLE 1 5 .
Developmental p e r io d o f grasshopper species from the Three F orks,
Montana stu d y s i t e - 1975.
I n s t a r s are re p re s e n te d in descending
A d u lts are re p re s e n te d by heavy l i n e s — .
o r d e r by t h i n I i n e s - —
Grasshopper
species
2
9
:'.\ y
16
23
30
6
.TVNF13
20
Psoloessa
dellcatula
30
7
JULY
14
21
28
I
AVCVST
8
15
I
22
I
SI?5
A<«n
Aulocara
elliotti
----==---%_________
Aaphltorqus
coloradus
A
<uI
— ---ZZ-------
Adult
Melanoplus
infantilis
Adu
Melanoplus
packardii
H
Adul t
Phlibostroma
Adui
quadrimaculatua
Melanoplus
saneulnlpes
________________________
----
Adull
Ageneotettlx
d e o rm n
*
Adult
Hesperotettlx
viridls
15
AduM
Ul
Ul
56
F i e l d r o o t e l o n g a t i o n f o r w e s te rn w heatgrass and n e e d le -a n d th re a d was h i g h l y v a r i a b l e .
The d a ta c o l l e c t e d by th e method,
employed were th o u g h t t o be u n r e l i a b l e .
The r o o t s would grow a g a in s t
th e g la s s f o r a s h o r t p e r io d o f tim e and then d ie back o r t u r n away
from th e g la s s .
The w e ekly measurements i n d ic a t e d an average d a i l y
r o o t grow th o f 10 mm p e r day.
However, t h i s
is a h ig h ly v a ria b le
fig u re .
D u ring mid J u l y th e r o o t s o f b o th grass sp e cie s n e a r l y stopped
grow ing a g a in s t th e g la s s panes a t th e tim e o f a n t h e s i s .
o c c a s io n a l e l o n g a t i o n was observed a f t e r t h i s d a te .
Only
No e s t im a t io n
o f e a r l y s p r in g (May) r o o t grow th was made; however, some rhizome
a c t i v i t y was noted d u r in g September.
■
SUMMARY AND CONCLUSIONS
G razing grasshoppers e x e r t an i n f l u e n c e upon th e p r o d u c t i v e
ran g e la n d ecosystem by t h e i r d e f o l i a t i o n o f p la n t s th ro u g h e a t in g
and d i s l o d g i n g p l a n t m a t e r i a l .
o f d e fo lia tio n :
T h is g r a z in g in c lu d e s f o u r aspects
i n t e n s i t y , fre q u e n c y , s e a s o n a l i t y , and s e l e c t i v i t y .
T h is s tu d y d e a ls m a in ly w i t h i n t e n s i t y and fre q u e n c y , a lth o u g h
s e a s o n a l it y was i n v e s t i g a t e d on a v e ry l i m i t e d b a s is .
Greenhouse and f i e l d
o b s e r v a tio n data were reco rd e d f o r two y e a rs
on v a r io u s phases o f g ra ssho pper g r a z in g o f Agropyron s m i t h i i
w h e a tg ra s s ) and S t ip a comata ( n e e d le - a n d - t h r e a d ) .
(w e ste rn
Based on t h i s
s tu d y th e f o l l o w i n g c o n c lu s io n s were f o r m u la t e d :
1.
Both greenhouse and f i e l d
d ata o f n e e d le -a n d -th r e a d grass
i n d i c a t e d t h a t as g ra ssho pper g r a z in g i n t e n s i t y in c re a s e d t h e r e i s
a gen e ra l r e d u c t io n i n t o t a l r o o t w e ig h t.
2.
,
A greenhouse s tu d y o f w e s te rn wheatgrass i n d i c a t e d t h a t
heavy g r a z in g (80 p e r c e n t removal o f to p g ro w th ) f o r a 16 day p e r io d
was th e most d e t r im e n t a l o f a l l t r e a tm e n t s s t u d ie d .
O b s e rv a tio n and
d ata found t h a t moderate r a t e s o f g r a z in g (50 p e rc e n t removal o f top
g ro w th ) and a o n e -tim e c l i p p i n g
( t o a 2 .5 cm l e v e l ) responded s i m i l a r l y
Western wheatgrass responded t o an in c re a s e i n grassho pper g r a z in g
i n t e n s i t y by ( I )
a r e d u c t io n in t o t a l
r o o t , crown, and rhizom e w e ig h t,
(2 ) r e d u c t io n i n maximum depth o f r o o t p e n e t r a t i o n , and (3 ) r e d u c t io n
58
o f th e number o f new shoo ts produced.
There were no s i g n i f i c a n t
d i f f e r e n c e s between th e l i g h t g r a z in g and un-grazed t r e a t m e n t s .
3.
I t was observed and reco rd e d t h a t on one s i t e lo c a te d in
south c e n t r a l Montana th e m a j o r i t y o f th e grasshopper d e f o l i a t i o n
p e r io d o c c u rre d a f t e r th e a c t i v e grow th p e r io d f o r th e two cool
season grass sp e c ie s s t u d ie d .
Grasshopper g r a z in g can reduce th e amount o f new r o o t s produced
d u r in g c e r t a i n grow ing stages o f grass s p e c ie s .
b r ie f in v e s tig a tio n , i t
However, fro m t h i s
I*
<
appears grassh o p p e r g r a z in g o ccurs l a t e
enough in th e developm ental sta g e s o f cool season grasses t h a t th e
in f l u e n c e o f t h i s d e f o l i a t i o n
had o c c u rre d e a r l i e r .
i s le s s d r a s t i c than i f d e f o l i a t i o n
>
3
3
TABLE 8.
Weights ( g m / p la n t ) o f n e e d !e -a n d - th r e a d crowns i n response
t o grassho pper d e f o l i a t i o n
.
( f i e l d d a ta ).
PLANTS NOT EXCAVATED
REPLICATE
3
TREATMENT
I
2
Un-grazed
Grazed
10.830
8.725
8.536
7.140
14.447
6.780
4
15.905
11.200
5
24.200
3.523
TOTAL
73.918
37.368
MEAN
14.783
7.473
ANALYSIS OF VARIANCE
DF
9
4
I
4
SOURCE
TOTAL
REPS
TREATMENTS
ERROR
MS
SS
309.945
52.526
133.590
123.829
133.590
30.957
F = 4 .3 1 5 ^
PLANTS PRE-EXCAVATED
TREATMENT
I
Un-grazed
Grazed
5.800
8.790
REPLICATE
3
2
13.915
15.237
4
11.745 13.105
10.073 - 3.805
5
9.035
9.185
TOTAL,
53.600
47.090
ANALYSIS OF VARIANCE
SOURCE
TOTAL
REPS
TREATMENTS
ERROR
DF
9
4
I
4
F=. 3 7 0 ^
I/
Not s i g n i f i c a n t (P .0 5 )
? ^ E e m g 3 » g ra » C T iB O T « « g ro » » B B a g a itB > g 8 i» y ia « is B C B B B a n ra B W ia > « B ^ ^
SS
114.475
64.477
4.238
45.760
MS
4.238
11.440
MEAN
10.720
9.418
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The response of
western wheatgrass and
needle and thread grass
to grasshopper defoliation