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 Georgia- Department
of Plant Pathology, P. O. Box 748, Tifton, GA 31793
Roundup Ultramax (glyphosate) and removed.
Using the same treatment design from the
previous crop, Vapam (metam sodium) was
drip-applied at 50 gal/A in the wheat treatment
on 31 July 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 done on 8 September
and vigor ratings were conducted on 20
September and 3 October. Plant vigor was rated
on a scale of 1 to 10, 10 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 tomatoes (6 July), and at
planting (11 August) and harvest (31 October)
of peppers. Nematodes were extracted from a
150-cm 3 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.
Introduction
Many plants in the Brassicaceae family
produce glucosinolates naturally.
Glucosinolates degrade into compounds such as
methyl isothiocyanates (M ITC) and allyl
isothiocyanates (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 in winter 2005
followed by a planting of Tomato in spring 2006
and the subsequenst squash crop in fall 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
wide with 5 foot alleys.
Brassica crops were radish (Scarlet
Globe), rapeseed (Dwarf Essex), rutabaga, and
mustard (Florida Broadleaf). Other treatments
were bare fallow and wheat with and without
Vapam. At the termination of the tomato crop,
all tomato plants and weeds were killed with
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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
(pim aricin -am p cillin -rifam p icin -P C N B ) for
isolation of Pythium species. One ml of the
second preparation was dispensed and spread
onto a petri plate containing a Fusariumselective 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 31 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 Tomato fruits 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, 2, 10, 17 and 26 October.
test. Root-knot nematode soil populations were
highest in the radish, mustard, and control
fallow treatments at planting and at harvest of
squash. Root damage resulting from infection
and feeding of root-knot was also highest in the
radish, mustard, and control fallow treatments
with the control fallow having the highest
overall level of root damage compared to the
other treatments. There were no significant
differences noted in fungal populations in the
soil among the treatments although the radish
and rutabaga at plant of squash and radish,
rutabaga, and rapeseed at harvest of squash had
the highest numeric populations of Pythium and
Fusarium in the soil than the other treatments.
Affects of the Brassica and nonBrassica treatments were also evaluated on
subsequent vegetable crop following tomato.
The results indicated that the rapeseed, rutabaga,
and wheat with Vapam treatments had the
highest yield in marketable number and weight
(numerically) with the control fallow and radish
treatment having the lowest yields in both
marketable fruit weight and number (Table 4).
Results for the evaluation of culled fruit showed
that mustard, control fallow, radish, and wheat
with Vapam treatments had the lowest number
and weight of culled fruit (Table 4). Results of
total fruit number and weight indicated that
rapeseed, rutabaga, and wheat with and without
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
treatment (Table 4).
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. Even
though there was an increase in nematode
populations and damage in some of the
treatments, the results are still questionable due
to the increased level of variability observed
both among and with treatments.
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 tomato crop. There
were few differences observed in plant stand
counts among the cover crop treatments.
However, in evaluating plant vigor among the
treatments radish, mustard, and control fallow
treatments were found to significantly limit plant
growth compared to the rutabaga treatments on
20 September and 3 October. The rutabaga
treatments had also a numerically higher level of
plant vigor than wheat treated with Vapam.
There was an increased level of rootknot nematode populations in the soil and root
damage in the subsequent vegetable crop in this
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