Controlling Weeds in Vegetable Production Using Spring Sown Cover
Crops as Killed Mulch.
Principal Investigator:
Dr. Mark Bennett, and Mary Christine Akemo, Dept. of Horticulture and Crop Science, O.S.U.
Abstract:
The use of cover crops in vegetable production in Ohio would reduce application of
herbicides for weed suppression, reduce soil and environmental pollution, and improve soil
structure and fertility. Most research on cover crops has been on those over-wintered and killed
in the spring for mulch. This study was repeated for the third time to determine if cover crops
sown in the spring and killed for mulch can control weeds well enough to produce acceptable
tomato yields. The unusually dry season and high weed pressure in the experimental plots
depressed tomato performance, though plots with higher pea proportions in the cover crop had
better yields than those with higher rye proportions. Yields were much lower than in 1997 when
soil moisture was adequate.
Materials and Methods:
Raised plots measuring 40ft by 4ft were established at OSU
Horticulture Farm on Lane Avenue in Columbus. Cover crops winter rye ' Wheeler' (Secale
cereale L.) and field peas (Pisum sativum L.) were sown on April 23 with ratios and seed rates
as shown in Table 1. There were 18 treatments including 3 controls, all replicated 4 times.
Percent ground cover by weeds was assessed visually 60 days after sowing cover crops (DAS).
Cover crop biomass was harvested 62 DAS from 0.5 m2 areas of treatments 1 to 15. Pea and
rye foliage were dried and weighed separately. Cover crops were undercut 63 DAS, and WT
and WFT were rototilled 73 DAS. One-month-old 'Marglobe' tomato (Lycopersicon esculentum
Mill.) seedlings were hand transplanted July 6 to 7, 50 plants per plot in 2 rows, 60 cm between
rows, 45 cm between plants. Disease control was carried out following recommendations for
the State of Ohio, and pests were controlled based on scouting. Tomato plants were
destructively harvested from all treatments 50 days after transplanting. Data was collected on
soil temperatures, flowering, and fruiting of tomato plants. WFT was hand weeded as required.
Ten plants from each plot were tagged for harvesting, and fruit was picked as it ripened. Weed
dry weight was taken at undercutting and 45 days after undercutting cover crops. Soil was
sampled before sowing cover crops, at cover crop cutting, and end-of-season.
Results and Discussion:
May was cold and dry, and the cover crops accumulated foliage
mainly in June. rpH and rPH had the highest cover crop dry weight, while PPL had the least
(Table 1). Before undercutting, grass weeds were very few or non-existent. Broad leaf weeds
were stunted by pure rye treatments but higher in numbers (data not shown). Weed dry weights
were higher 45 days after undercutting cover crop that at undercutting (Table 2). Soil
temperatures did not vary much, ranging between 20 and 25 C the whole season.
This year dry weather and high weed pressure after transplanting suppressed tomato growth in
all cover cropped treatments compared to WFT and WT (Table 3). Fifty days after transplanting
tomato plants from WFT and WT had highest leaf areas, followed by PPM, PPH, and rPH. This
was probably due to the nitrogen supplied by the field peas in these treatments. Dry weight of
tomato plants in cover cropped treatments was more comparable to that obtained in the weedy
check (WNT) than in WT and WFT. Tomato plants flowered and fruited 2 weeks earlier in WT
and WFT than in the cover cropped treatments and WNT (data not shown). rPH and rpH had
next fastest rate of tomato plant flowering and fruiting. WFT and WT out-yielded WNT and the
cover cropped treatments, except rPH (Table 3).
N, P, and K soil levels were higher in most treatments at undercutting than before sowing cover
crops, while N and P levels were lower at the end of the season (Table 4). Ca, Mg, and CEC
levels were also higher at undercutting cover crops and had fallen by the end of the season
(data not shown).
Weeds and cover crops have to be killed completely at mowing or undercutting otherwise they
re-establish and suppress vegetable growth. This year rain the same evening the cover crops
were undercut especially favored re-establishment of the broad leaf weed species.
Undercutting must be timed to allow cover crops and weeds enough time to dry out before the
soil receives any moisture. At least three days are required for cover crop and weed kill after
undercutting. Adequate soil moisture is also essential after establishment of the primary crop
for acceptable yields. These results showed that in a dry year cover crops may not adequately
offset the effect of deficient soil moisture on crop growth and yield.
Extension Program Implementation:
These results will be presented in seminars in the
Department of Horticulture and Crop Science, at 1998 horticulture meetings such as the Ohio
Fruit and Vegetable Growers Congress, and the American Society of Horticultural Science.
For further information contact Mark Bennett, Associate Professor, Horticulture & Crop Science or the Ohio IPM Office.
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