Effects of Season and Rate of Application
of 2,4:-D and 2,4,5-T on Pine Seedlings
and Mountain
Whitethorn
Frank J. Baron, N. Stark,
and Gilbert
H. Schubert
in California
Abstract. Intermingled pines and mountain whitethorn were treated with foliar
sprays of 2,4-D and 2,4•5-T to test their effectsaccordingto (1) seasonof year,
(2) concentrationof spray on individual tree-brushclumps,and (3) spray
dosageapplied on an area basis. Spraying with 2,4,5-T in Septetnberresulted
in the besttree growthand mostbrushkill; 2,4-D causedthe mosttree damage
and was less effective as a brush killer.
The best brush kill
resulted from
application rates of 400 to 600 ppm of 2,4,5-T, but these concentrationsreduced
Ow.a •ucn
of the Stanislaus-Tuo-
tree growth. After two full growing seasons,average height growth of the
pines was greater on plots receivingfrom •/4 to 1 pound of 2,4,5-T per acre
lumne Experimental Forest, eastof than on the control plots. Application rates of 2 and 4 pounds per acre (ppa)
Sonora,Calif., the growth of natu- gavebestbrushkill but causedseveredamageto the pines.
ral conifer reproduction is markedly hampered by associatedbrush
species. The Forest is typical of
the mixed-conifertype of the westside central Sierra Nevada.
We
damage to the overtopped conifers. cense-cedar ( Libocedrus decurrens
now have hope for releasing these Now, aerial spraying to release Torr.). The brush is predominanthandicapped trees from brush corn. conifers from brush competition ly mountain whitethorn (Ceanopetition
will undoubtedly be one of the thus cordulatusKell.), with some
A most convenient
•nethod of
most profitable uses for herbicides littleleaf c e a n ot h u s (Ceasethus
controlling unwanted brush is to on forest lands in southwestern
parvifolius [Wats.] Trel.).
destroy or suppress it by chemical Or•egon(7, p. 74). Increaseduse
The responses of intermingled
weedkillers.
But the use of •veedalso is being made of aircraftpines and brush plants to foliar
killers in wildland management applied herbicides to release•coni- applications of 2,4-D or 2,4,5-T
calls for a combination
of "the
fers from competinghardwoodsin were tested in the different studies
right herbicide, in the right con- the Lake States (8).
involving effects of (a) seasonof
centration, at the right time" (1).
Preliminary screening of chem- year, (b) concentration of spray
The problem is compoundedwhen ical treatments is most convenientapplied to individual pines growherbicide-sensitive conifers also oc- ly and economicallyperformed on ing in clumps of brush, and (c)
cupy the site along with "weeds." single plants becausemore combi- spray dosagewhen applied to trees
Climatic and edaphic variabilities nations of treatments are possible and brush on an area basis.
further complicate the California on a limited area of uniform site
Throughout all thesetests,butoxybrushproblem(7, p. 86). Although characteristics, and most effective ethanol esters of 2,4-D or 2,4,5-T
blisterrust controltestshaveyielded muchbasicdata on the response
of R•ibes
spp.to chemicals(6), relatively few tests have explored
chemicalcontrol of the variety of
other brush speciesprevalent in
the Stanislaus-TuolumneExperimental Forest (9, 10).
Much
useful brush control in-
formation has come from herbioide
tests elsewhere (10). One of the
earliest reports on aerial release
for conifers was that by Hawkes
(5) on the Oregoncoast.IIe found
that an aerial application of 2
pounds of 2,4-D acid per acre
killed aid(Jr,but did very little
THE AUTIIOR,q
are, respectively, research
forester, botanist,and re.s•m-r•4•
forester,
Pacific Southwest Forest and Rn•ge
Expt. St,q, Forest Service,U.S. Dept.
Agric., Berkeley, Calif. Mr. Schuhcrt's
present address: Rocky Mmmtain Forest
and Range Expt Sta., Flagstaff, A•iz.
use is made of limited
time
and
were mixed
in water
as a carrier
materials. Moreover, application and applied to the trees and brush
rates can be converted approxi- by using a backpack pump. All
mately to an area basisby assum- treatments were applied before 8
ing application of fixed amounts of a.m. to minimize evaporation losses
Initial heights of all test trees
chemical per plant and estimates
of bare ground and numbers of were measuredbefore spray applications and compared to subseplants per acre.
This paper reports results of quent measurementsin September
some recent California
tests and
of each year thereafter. Concurshows how this infomnation can
rently, we estimated damage to all
be related to data from other areas
the brush as a percent of stems
in developing chemical control killed (dried and brown) for each
measuresfor local speciesof brush. brush plant.
Seasonl s t u d y. -- Treatments
Materials and Methods
were assigned at random to indiThe major conifer specieson the vidual tree-brush clumps, each contest area are: sugar pine (Pi•ots sistin,-, of a single, youn,o.sugar
lambertiana Dougl.), ponderosa pine, 2 to 3' feet tall, surrounded
pine (Pin,rs po•idcrosaLaws.), Jef- by a mature mountain whitethorn
frey pine (Pin•ts jeffreyi Grey. & plant. At monthly intervals durBall.), white fir (Abies concolor ing 1958-•959, five clumps were
[Gord & Glend] Lindl ), and in- drenched with 2,4-D and five with
472
JuLY 1964
473
Concentration study.--The best accessto soil water. Height incre2,4,5-T at a concentrationof 200
brush
kill resulted from applica- ment of sugar pine was lessthan
ppm. Ten untreated controlsand
10 mechanical brush removal rep- tions of 400 to 600 ppm of 2,4,5-T, that of the control in plots receivbut at this concentration tree seedlieations were also established. The
ing the 2 ppa rate, and the 4 ppa
mechanical
brush removal
treatling growth was inferior to con- rate killed most of the trees. The
ment consistedof removing the en- trol growth. The height growth of survival of sugar pine also detire top of the brush plant, in- sugar pines receivingthe 100 ppm clined as chemicalapplication was
cluding the root crown. For com- application of 2,4,5-T was some- increased,particularly at rates of
parison with mechanicaland chem- what greater than that of the con- 2 and 4 ppa.
Ponderosapine respondedsimilical tests, the controls furnished trol trees, although the associated
data on growth and development brush was not damaged severely arly to sugar pine, but the data
of trees not released from brush
(Table 2). None of the 2,4-D tests are not as complete. Application
resulted in height growth of trees rates of •/• and x/• ppa resulted in
competition.
Concentration study.--In Sep- excelling that of the controls or in heightgrowthgreaterthan that of
the controls, but the 4 ppa rate
tember 1958, five concentrations effective kill of mountain whitekilled several trees.
thorn.
The
highest
concentration
each of 2,4-D and 2,4,5-T were
Supplementaryobservations
intested: 50, 100, 200, 400, and 600 of 2,4-D (600 ppm) seriouslydamppm. For each chemical and con- agedthe pine seedlings,killing the dicated that white fir was highly
to herbicides.Perhaps
centration combination, five ran- leaders and resulting in negative susceptible
these
trees
can
be chemicallyweedheight
growth.
The
most
height
domly selected tree-brush clumps
ed
out
of
pine
stands.
growth
for
sugar
pine
sprayed
with
were sprayed thoroughly to the
Only
one
species
of brush other
2,4-D
was
achieved
with
the
100
runoff point. Ten unsprayedtreethan mountain whitethorn was obppm rate.
brush clumps servedas controls.
Broadcast study. -- Brush kill served: littleleaf ceanothus. It was
Broadcaststudy.--Six 1/10-acre
killed by all treatmentsusingmore
plots were established in an area was low in the plot receiving the
than I ppa of herbicide.
where brush cover, topography, l• ppa treatment. Application
Discussion
age, and density of natural conifer ratesof 2 and 4 ppa gavesuperior
reproduction were approximately brush kill but caused more severe
These results conform to patuniform. The plotsweremapped, reductionin tree growth (Table 3). terns set by earlier work in this
marked with stakes, and random- After two full growing seasons,
localityaswell asin Oregon.Both
ly assigneddifferent dosagesof average height growth for sugar
Schubert(9) and Gratkowski(3)
2,4,5-T: 0, 1/•, 1/•, 1, 2, and 4 pounds pine was greater in the plots re- found that 2,4,5-T was superiorto
per acre (ppa). The appropriate ceiving from •/• to l•pound of
2,4-D in controlling mountain
amount of herbicide was applied herbicideper acrethan that in the whitethorn. Schubertreported that
in September
'1959, using 50 gal- control plot. Initially, the sugar
applications
in fall producedthe
lons of carrier per acre to cover pinesin the •/• ppa test averageda most reduction in foliage, but very
fully each plot, including bare foot taller than the controls. These few roots were killed even at rates
taller treesmay have had superior
ground.
root systems, providing greater of 2,000to 3,000ppm. Brushkill
may not haveto be completeto reResults
leaseconifers(9). It appearsthat
Seasonalstudy.--Good kill of the TABLE 1.--GROWTH OF PINE ANDDAMAGE
brushstems,with little respouting, TO BRUSH
occurred
in
the
treatments
with
PLANTS RECEIVING AQUEOUS
FOLIAGE SPI•AYS OF BUTOXY'IErfHANON
ES•q•RSOF 2,4-D AND 2,4,5-T APPL•ZD•N
TABLE 2.--GROW?H oF PINE AND DAMAGE
TO BRUSH PLANTS RECEIVING DIFFERENT
CONCENTBATIONSOF AQUEOUS I•OLIAGE
SPRAYS OF BUTOXY-ETHANOL ESTERS OF
2,4,5-T appliedfrom May through VA•OUS Mo•s
AT A CONCEN•A•ON
O• 200 PPM x
September (Table 1). Little tree
2,4-]) AND2,4,5-T IN SEPTEMBF•
x
seedlinginjury occurredfrom 2,4,
Sugar pine
Whitethorn
Sugar pine
Whitethorn
5-T, exceptwhen applied in June Treatment heightgrowthe foliage.killa
Treatment
e heightgrowth• ' foliagekill•
and July. The September2,4,5-T
Percent of control
Percen• of •on•rol
application resulted in especially 2,4-D
superior tree growth and brush
April ............
50
2
kill. These trees exceeded the aver-
May ..............
60
72
Jtme
4
74
34
15
94
4
36
15
age control height growth by 43
percent and that from mechanical
brush removalby 25 percent. In
contrast, poor brush kill resulted
from all 2,4-D testsexceptin May
and June, when both brush and
tree seedlingswere damaged. The
pines were injured severely by 2,4D at all application dates except
in September, although even then
the average height growth lagged
behind that of the controls.
............
July ..............
August ........
September....
2,4,5-T
April ............
May .............
92
85
31
100
June
..........
44
86
July
...........
28
88
113
143
80
92
118
100
August ........
September....
Mechanical
......
XEvaluated 3 years after application.
•A difference of 12 is significant at the
5-percent level.
aA difference of 7 is significant at the
5-percent level.
2,4-D
50
100
200
400
................
................
..............
................
600 ...............
2,4,5-T
50 .............
100
200
400
600
................
............
................
................
62
82
67
47
0•
0
0
12
9
46
67
5
105
46
52
70
56
52
92
89
XEvaluated3 years after application.
-øExpressed
as parts per million.
SA difference of 9 is significant at the
5-percent level.
*A difference of 13 is significant at the
5-percent level.
•Leaders killed.
474
Jov•m
TABI•E 3.--EF•EC•
OF DIFlVERENTAPPLICATIONRATES OF 2,4,5-T ON GROWTHAND
•[URVlVAL
OPSUGARPrNE ANDPONDEROSA
PINE ANDOIqBRUSHCONTROL
1
Application
rate
Sugar
pine
Ponderosa
pine
Height growth
Survival
0
29
100
28
100
•/•
•
33
33
100
97
48
31
100
100
i
2
37
6
96
85
Pounds/acre
Height growth
Survival
Percent of original
o'
.......
--0
OF FORESTRY
5. Increasing the 2,4-D concentrations of the September spray
to 600 ppm killed only about half
Mountain
whitethorn the brush and most of the pine
foliage kill
leader growth. Application of 2,4,
5-T at 100 ppm resulted in pines
0
growing more than did the con20
trols, although brush kill was low,
30
85
suggestinghormonal stimulation.
98
6. For broadcastapplicationsof
lOO
2,4,5-T, brush kill increased from
XEvaluated 2 years after application.
20 to 100 percent as dosagewas in-
'Leaders killed.
creasedfrom 1/•to 4 poundsperacre
(ppa). Height growth of sugar
pines receiving 1/• to I ppa exceedsufficiently to allow the trees to riers were used with the esters of ed that of the untreated controls,
become dominant (3, 8).
the two chemicals in this study. whereas the 2 ppa rates reduced
Not only was 2,4,5-T more dam- Addition of oil would have en- growth, and the 4 ppa rate killed
aging to whitethorn than was 2,4-D, hanced brush kill, but would also the new leaders. The poor brush
but it was also less damaging to have resulted in more damage to kill at 1/• ppa again suggestsa hormonal stimulation of pine growth
sugar pine, when applied in a wa- the conifers (2).
Only one speciesof brush was or greater initial height.
ter carrier. Anotherfavorablepoint
was the ability of sugar pine seed- tested here, but comparablyfavorLiterature
Cited
low application rates repeated at
which are still the "work
horses"
intervals may suppressthe brush of the weedkillers. Only water car-
lings to recover even when dam-
able results have been obtained on
similar speciesin earlier years (9)
especially sugar pine, have been and in other areas (3). Prompt acconsideredparticularly sensitiveto tion seemsadvisablein preventing
herbicides (4). Our results do not the brushfrom becomingtoo large.
bear out this belief. The trees and
Seedlings and sprouts are easier
brush were heavily drenched. But to control than the large, mature
in actual practice the trees prob- plants (9). If a control program
ably would be at least partially were begun immediately after
screenedby the brush (5). There burns or logging, very little old
even appeared to be an enhanced brush would be present.
rate of growthafter the lighter apSummary and Conclusions
1. BRINK•AN,
aged by herbicides. The pines, and
plications. In view of the relative-
oak brush.
1959.
Forest
Killing
Serv.
Cen-
cud Range Expt. Sta. Res. Paper 39.
17 pp.
3. GRATOWSKI, I:[.
1959.
Effects
herbicides on some important
of
brush
species in southwestern Oregon.
U.S. Forest Service, Pacific Northwest Forest and Range Expt. Sta
Res. Paper 31. 33 pp.
4.
--.
1961. Toxicity of herbicides on three northwestern
coni-
5. HxwKEs,
2. The 2,4,5-T applications consistently caused more damage to
of weeds is obtained slowly because the brush, and less to the pines
of the many variables involved than did 2,4-D. In addition to the
(11). Delayed action effectsmay type of chemical, other factors afnot show up for 2 to 3' years or fecting results were concentration
7.
fers. U.S.
Forest Service, Pacific
Northwest Forest and Range Expt.
Sta. Res. Paper 42. 24 pp.
C.
1953.
tree plantation.
Planes
release
Jour. Forestry 51:
345-348.
6. OFPORD,H. R., V. D. Moss, W. V.
BENEDIC% and OTHm•S. 1952. Improvements in the control of Ribes
by chemical and mechanical means
L'. S. Dept. Agric. Cir. 906. 72 pp.
has discussedthe theory of such different dosages.
stimulation.
Information
A.
tral States Forest Expt. Sta. Tech
Paper 165. 9 pp.
2. DAHMS, W. O. 1961. Chemical control of brush in ponderosa pine forests of central Oregon. U.S. Forest
Service, Pacific Northwest
Forest
1. Low volatile esters of 2,4-D
brush, this height increase seems or 2,4,5-T in a water carrier were
more likely to be the result of hor- applied to mature mountain whitemonal stimulation r a t h e r than
thorn plants in intermingled, 10year-old
sugar pine reproduction
greater availability of soil moisat
various
times of the year and at
ture or nutrients (2). Woods (11)
ly light damageto the surrounding
K.
U.S.
on chemical control
Illus.
O•F. OON STATE
UNiVErSiTY.
1961
Herbicides and their use in forestry
Symposium, Agric. Expt. Sta. and
School of Forestry, Ore. State Unlv,
Corv,Mlis.
122 pp.
more after application. Repetition of chemicaland month of applicaof treatments in different years is tion.
3. From 80 to 100 percent of
sometimes necessary because of
8. RoE, E. I. 1961. Releasing Conifers
the brush stems were killed by sin-
9. SCHUrE•%G. H. 1955. Recent trials
with 2,4-D and 2,4,5-T to kill brush
weather
v a r i a t i o n s.
Seasonal
in the Lake
U.S.
States with
chemicals
Dept. Agric. Hdbk. 185. 22
pP.
changes in air and soil tempera- •le applicationsof 200 ppm of
in the Sierra Nevada in California
2,4,5-T in any month from May
U. S. Forest Service, California
Forest and Range Expt. Sta. Res.
through September.
pp.
4. Sugar pine height growth ex- 10. Note 102. 7 1962.
Chemicals for
brushcontrolin Californiareforthe height growth of sugar pine on ceeded that of the untreated conestation. U.S. Forest Service, Pathe area of the seasonal study was trols after August or September
cific Southwest Forest and Range
noticeably greater than that in the applicationsof 2,4,5-T. The SepExpt. State. Misc. Paper 73. 14 pp.
concentration study on a drier site tember 2,4,5-T spray resulted in 11. WooDs, F. W. 1955. Control of
woodyweeds.Somephysiologicalasgreater pine height growth than
a short distance away.
pects. U'. S. Forest Service,Southwhen
the
brush
was
removed
meThese results are based on only
ern Forest Expt. Sta. Occas. Paper
ture, as well as moisture fluctuations, may effect herbicide work
(6). As an example, we noted that
two herbicides,2,4-D and 2,4,5-T, chanically.
143. 50 pp.