2007 Extension Research Report
Disease Management
EVALUATION OF BRASSICA COVER CROPS FOR CONTROL OF
SOILBORNE PEST AND DISEASES ON SUBSEQUENT SQUASH
W. S. Monfort, A. S. Csinos, A. R. Barrentine, and Lara Lee Hickman, University of GeorgiaDepartment of Plant Pathology, P. O. Box 748 Tifton, GA 31793
wide with 5 foot alleys.
Brassica crops were radish (Scarlet
Globe), rapeseed (Dwarf Essex), rutabaga,
and mustard (Florida Broadleaf). The other
treatments were bare fallow and wheat with
and without Vapam. At the termination of
the pepper vegetable crop, all pepper plants
and weeds were killed with Roundup
Ultramax (glyphosate) and removed. Using
the same treatment design from the previous
crop, Vapam (metam sodium) was dripapplied at 50 gal/A in the wheat treatment
on 26 June prior to planting. Plastic covered
plots were 25 feet long and 30 inches wide.
Squash cv. “Prelude II”seedlings
were purchased from Lewis Taylor Farms in
Tifton. A single plant was transplanted
using a mechanical type transplanter, which
cuts holes in the in the plastic just ahead of
the planters in the center of the plastic bed
adjacent to the drip tape on 16 August.
Plant spacing was 12 inches. All plots were
injected with Admire (4oz/A on 18 August)
and sprayed with Phaser (1 Qt/A on 25
August, and 5, 11, 18, and 25 September),
Pounce 3.2 (Permethrin) (8 oz/A on 16
October), Capture 2 EC (Bifenthrin) (5 oz/A
on 1, 6, 13, 20, 27 September and 6 and 10
October), and Intruder (Acetamiprid) (2
oz/A on 8, 15, 22, and 29 September) for
insect control.
Stand counts were recorded on 20
September and vigor ratings were conducted
on 20 September and 3 October. Plant vigor
was rated on a scale of 1 to 10, 10
Introduction
Many plants in the Brassicaceae
family produce glucosinolates naturally.
Glucosinolates degrade into compounds
such as methyl isothiocyanates (MITC) and
allyl i s ot hi ocyan at es (AITC).
Both MITC and AITC are lethal to
soilborne pests such as nematodes and fungi.
In fact, the common fumigant metham
sodium degrades to MITC and then accounts
for its activity as a soil fumigant. Since the
Brassica species have been demonstrated to
produce glucosinolates which degrade into
MITC and AITC there is interest in
determining if the growing a Brassica crop
prior to another crop susceptible to soilborne
pests would benefit from the rotation. This
test evaluates the effect of Brassica species
grown prior to pepper. The Brassica cover
crop was planted during the winter 2005
followed by a planting of pepper in spring
2006 and the subsequenst squash crop in the
fall of 2006.
Materials and Methods
The study was located at the Tifton
Vegetable Park Farm, CPES, Tifton, GA.
The area has a history of assorted vegetable.
The area was prepared using all current
University of Georgia Extension Service
recommendations.
The test was a
randomized complete block design
consisting of single bed plots replicated four
times. Each plot was 25 feet long and 6 feet
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representing live and healthy plants and 1
representing dead plants.
Twelve soil cores, 2.5-cm-diam H
25-cm-deep, were collected from the center
of each plot at harvest of pepper (14 June),
and at planting (11 August) and harvest (23
October) of Squash. Nematodes were
extracted from a 150-cm3 soil sub-sample
using a centrifugal sugar flotation technique.
Soil fungal assays were conducted using a
sub sample from the collected soil. Aliquots
of soil were removed from each sub sample
and air dried for 24 hours. Five grams of
dry soil were added to 100 ml of 0.3% water
agar and mixed thoroughly. Immediately
afterward, 1 ml of soil/agar was removed
and mixed with 20 ml of 0.3% water agar.
One ml of the first preparation was
dispensed and spread evenly onto a petri
plate containing an oomycete-selective
medium (pimaricin-ampcillin-rifampicinPCNB) for isolation of Pythium species.
One ml of the second preparation was
dispensed and spread onto a petri plate
containing a Fusarium-selective medium
(peptone-PCNB).
Fungal plates were
incubated for 120 hours for Fusarium
species and 48 hours for Pythium species.
After incubation, CFUs were counted and
recorded.
On 19 October a root gall evaluation
was conducted on three plants per plot using
a 0 to 10 scale, whereby, 0 = no galls, 1 =
very few small galls, 2 = numerous small
galls, 3 = numerous small galls of which
some are grown together, 4 = numerous
small and some big galls, 5 = 25 % of roots
severely galled, 6 = 50 % of roots severely
galled, 7 =75 % of roots severely galled, 8 =
no healthy roots but plant is still green, 9 =
roots rotting and plant dying, 10 = plant and
roots dead.
All squash fruit were hand harvested
from the 10 foot center area of each bed.
Each harvest was separated into marketable
and cull fruits, counted and weighed. There
were a total of four harvests, 29 September
and 6, 12 and 19 October.
Results and Summary
This test was conducted to evaluate
the affects of Brassica and non-Brassica
cover crop treatments on subsequent crops
in a double crop vegetable system. Yellow
squash was planted in the fall following a
spring pepper crop.
There were little
differences observed in plant stand counts
on 20 August and plant vigor on 20
September among the cover crop treatments.
However, in evaluating plant vigor on 3
October among the treatments the control
fallow treatment was found to significantly
limit plant growth compared to the radish
and rapeseed treatments. The radish and
rapeseed treatments also had a numerically
higher level of plant vigor than the wheat
treatment with Vapam.
Like with the previous pepper crop
there was no detectable level of root-knot
nematode populations in the soil or root
damage observed in this test location. In
examining the affects of the treatments on
soil fungal populations there were a
significant higher level of Pythium
populations noted in the soil in the rapeseed
and control fallow treatments at plant of the
squash crop compared to wheat treatments
with Vapam. By harvest time of the squash
crop, there were little differences in Pythium
populations observed among the treatments.
For Fusarium, there were no significant
differences observed at plant of squash,
however numerically, the control fallow
treatments had the lowest overall
population. The control fallow and wheat
treatments had the lowest populations at
harvest of the squash crop.
Affects of the Brassica and
non-Brassica treatments were also evaluated
on subsequent vegetable crop following
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pepper.
The results indicated that the
rapeseed, rutabaga, radish, and the wheat
with Vapam treatments had the highest yield
in marketable number and weight
(numerically) with the control fallow and
mustard treatment having the lowest yields
in both marketable fruit weight and number
(Table 3). Results for the evaluation of
culled fruit showed that the mustard
treatment had both the highest number and
weight of culled fruit than a majority of the
treatments evaluated (Table 4). Results of
total fruit number and weight indicated that
the rapeseed and the wheat with Vapam
treatments had the highest number of fruit
and fruit weight numerically compared to
the other treatments with the lowest fruit
number and weight being recorded in the
control fallow and wheat treatments (Table
3).
The results of this test indicated that some
cover crop treatments had a beneficial affect
on crop growth and yield. This increase in
crop growth and yield might be the result of
increased biomass and/or nutrients. The
impact of the Brassica and non-Brassica
treatments varied some between the
treatments in the subsequent crop as
compared to the first vegetable crop on crop
vigor and yield. With little to no nematode
and fungal pressure observed in this trial, no
conclusions could be made on the
nematicidal and/or fungal activity of the
treatments.
Table 1. Effect of Brassica Spp. on Plant Vigor and Stand Counts on “Prelude II” Squash,
Fall 2006, Tifton, GA
b
Vigor Rating b
Application Stand Countsa Vigor Rating
(0 to 10)
(0 to 10)
Treatment
Rate
Aug. 20
Sept.
20
Oct. 3
(gal/A)
Radish
28 Ac
Rapeseed
28 A
6.9 A
7.6 A
Rutabaga
28 A
5.8 A
6.8 AB
Mustard
28 A
6.6 A
6.9 AB
Control Fallow
26 A
5.5 A
5.8 B
Wheat
27 A
6.0 A
6.3 AB
Wheat and
Vapam
50
27
6.4
A
6.3
Ac
A
7.4
6.5
Ac
AB
a. Counts of live plants were taken on 20 Aug.
b. Vigor was done on a scale of 1-10 with 10 = live and healthy plants and 1 = dead plants
and an average was taken of vigor for 20 Sept. and 3 Oct .
c. Data are means of four replications. Means in the same column followed by the same
letter are not different (P = 0.05) according to Fishers’s LSD.
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Table 2. Effect of Brassica Spp. on Fungal Soil Populations (CFU/g soil) on “Prelude II” Squash, Fall 2006,
Tifton, GA
Harvest Peppera
At Plant Squashb
Harvest Squashc
App.
29 June
11 Aug.
23 Oct.
Treatment
Rate
Pythium
Fusarium
Pythium
Fusarium Pythium Fusarium
(gal/A)
species
species
species
species
species
species
Radish
4
Ad
3660 Ad
34 ABCd
Rapeseed
0
A
4540 A
53 A
Rutabaga
2
A
1400 A
Mustard
0
A
Control Fallow
3
Wheat
Wheat and Vapam
50
580 Ad
3 Ad
1.3 ABCd
4700 A
1 A
1.7 A
44 ABC
1740 A
3 A
0.8 ABC
1280 A
42 ABC
260 A
2 A
1.3 ABC
A
1640 A
46 AB
40 A
1 A
0.5 BC
3
A
1900 A
30 BC
3900 A
4 A
0.4 C
21
A
4400 A
26 C
320 A
2 A
1.5 AB
a. The at harvest of Pepper soil sample as taken on 29 June.
b. The at plant Squash soil sample was taken on 11 Aug.
c. The at harvest Squash soil sample was taken on 23 Oct.
d. Data are means of four replications. Means in the same column followed by the same letter are not different
(P = 0.05) according to LSD.
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Table 3. Effect of Brassica Spp. on Yield of “Prelude II” Squash, Fall 2006, Tifton, GA
Treatment
App.
Rate
(gal/A)
Marketable Fruita
Cull Fruitb
Number
Number
Weight (lbs)
Total Fruitc
Weight (lbs)
Number
Weight (lbs)
Radish
134 ABd
62.9 Ad
52 B d
17.8 ABd
186 Ad
80.7 Ad
Rapeseed
146 A
61.1 AB
68 AB
19.8 AB
214 A
80.9 A
Rutabaga
134 AB
55.8 AB
62 AB
14.1 B
196 A
69.8 AB
Mustard
94 B
26.8 A
193 A
68.0 AB
41.2 B
100 A
Control Fallow
113 AB
52.2 AB
59 B
16.0 AB
172 A
68.2 AB
Wheat
120 AB
44.1 AB
53 B
12.8 B
172 A
56.9 B
136 AB
55.8 AB
65 AB
17.4 AB
201 A
73.2 AB
Wheat and Vapam
50
a. The fruit from each individual plot that was considered to be marketable and showed no symptoms of disease were
separated, counted and weighed on 19 Oct.
b. The fruit from each individual plot that was considered to be non-marketable and diseased was separated, counted,
and weighed on 19 Oct.
c. The number and weight of marketable and non-marketable fruit were totaled for each plot on 19 Oct.
d. Data are means of four replications. Means in the same column followed by the same letter are not different
(P = 0.05) according to Fisher’s LSD.
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