Controlling Weeds in Vegetable Production Using Spring Sown Cover Crops as Killed Mulch

Controlling Weeds in Vegetable Production Using Spring Sown Cover Crops as Killed Mulch

Principal Investigators:

Dr. Mark Bennett and Mary Christine Akemo,
Dept. of Horticulture and Crop Science, O.S.U.

Abstract:

Weed control is a very important factor in profitable vegetable production, and herbicides are used by most vegetable growers in Ohio for this purpose. Using cover crops for weed control would result in the reduction of herbicide use, while also improving soil structure and fertility, and reduction of soil and environmental pollution. Most research in this area has been on over-wintering cover crops killed in the spring for mulch. The objective of this project was to determine if cover crops sown in the spring and killed for mulch can control weeds well enough to produce acceptable tomato yields. From the results treatments with field peas as cover crops produced better or comparable yields to the hand weeded control, even though weeds overcarne the mulch halfway through the season. The results confirmed observations form a previous experiment in 1996 with the same treatments.

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) and field peas (pisum sativum) were sown on April 24^th in the different ratios and seed rates shown for treatments in Table 1. There were 18 treatments including 3 controls, all replicated 4 times. On June 24^th cover crop biomass was harvested from 0.5 sq.m areas of treatments 1 to 15. Peas and rye foliage was dried and weighed separately. Cover crops were undercut on June 25^th and treatments 17 and 18 were cultivated with a rototiller. One month old seedlings of the tomato variety Marglobe were hand transplanted on June 26^th to 27^th, 50 plants per plot in 2 rows, with a spacing of 2 ft between rows and 1.5 ft between plants. Disease control was carried out following recommendations for the State of Ohio, and pests were controlled based on scouting. Toronto plants were destructively harvested from all treatments on July 31^st and August 1^st, and tomato leaves to= the tips of the plants for tissue nutrient analysis picked on August 19^th. Data was collected on soil temperatures, flowering, fruiting and fruit ripening of tomato plants. Treatment 18 was hand weeded as required. Ten plants from each plot were tagged for harvesting, and fruit was picked as it ripened. Soil samples were taken before sowing the cover crops and at the end of the season.

Results And Discussion:

Data from the experiment is summarized in Tables 1-4, and Figures 1-5. May was a cold month and the cover crops put on foliage mostly in June. Before undercutting, the rye was seen to suppress many weeds, especially the grasses. The broad leafed weeds also growing in the rye were stained compared to other treatments. Treatment 10 had the highest cover crop dry weight, while treatment 9 had the least ( Fig 1). The treatments with denser cover crop biomass on the soil surface had lower soil temperatures ( Fig 2), but towards the end of July, due to heavy rain, much of the cover crop mulch had decomposed. For both soil samplings ( Table 2), Rep 4 had lower readings for most of the elements and the CEC, causing the highly significant differences in replicates. End of season values for P and K were slightly higher, while those for Ca, Mg, and CEC were lower. N results were not yet available by the time of writing this report.

One month after transplanting tomato plants form treatments 10, 11, 13, 14, and 15 had highest leaf areas, while treatments 7, 10, 11, 13, and 14 had highest plant dry weights (Table 3). This was probably due to the nitrogen supplied by the field peas in these treatments. Tissue analysis was done when some treatments had tomato plants already flowering and this could have affected distribution of nutrients in the plants. Tomato plants from treatments 5, 7, 9, and 18 had highest levels of nitrogen in their leaves. Treatments 4, 7, 10, 14, and 18 achieved 50% flowering earliest, while 9 and 16 were the latest ( Fig 3). Treatments 7, 10, 12, 14, and 18 reached 50% fruiting earliest ( Fig 4). Apart from treatment 18, this can be attributed to the nitrogen fixed in the soil by the peas cover crops in these treatments. Plants in treatment 19 had no weeds to compete with. Ripening was again faster in the same treatments ( Fig 5). From Table 4, treatments 10, 19, 14, 15, and 7 had the highest yields by weight, while 10, 18, 13, 14, and 2 had the highest fruit numbers. There were no significant differences in the TSS analysis.

Though the cover crops decomposed about one month after undercutting and weeds grew, tomato plants in treatments with field peas grew faster and established dense canopies which contributed to weed control. They yielded better or comparable to the hand weeded control ( treatment 18). These results further strengthen the possibility of using spring sown cover crops for weed control in tomato production, and maybe even other vegetable crops. The tomato fruit yields of 45 to 52 metric tons per hectare are quite encouraging.

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, Dept. of Horticulture & Crop Science, The Ohio State University or the Ohio IPM Office.

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