INHS Reports July-August 1997

Cover-crop Mulches for Alternative Production of Vegetable Crops

We have all seen those idyllic, advertisers' dream pictures of row after row of lush vegetables highlighted crisply against a backdrop of bare earth. But the conventional tillage methods used to produce such crops can increase soil erosion, reduce soil quality, and require extensive amounts of pesticides, fertilizers, and water. Cover crops with reduced tillage have been used in many agricultural systems to reduce soil erosion, improve soil properties, add organic matter, and control weeds. Planted in fall or spring, they are plowed under as a "green manure," left as a killed mulch on the soil before planting the main crop, or grown as a living mulch between rows of the main crop. Vegetable growers have been slower than field-crop producers to adopt such practices because of lack of crop-specific information on the competitiveness, yields, and pest problems associated with these alternative practices.


Cabbage planted with wood shavings used as an inert mulch.

To address this concern, researchers at the Illinois Natural History Survey and the University of Illinois have been conducting field trials to compare vegetable crops grown in reduced tillage/cover-crop mulch systems with those grown in conventional tillage systems. Because these mulches alter the microclimate of the vegetable crop, the research has also focused on determining whether weed, insect, and disease problems affecting the crop are lessened, or (shudder!) made worse, by these alterations. Snap bean and cabbage were chosen because they are important fresh-market and processing crops in Illinois and represent different plant families with different pest problems. Cereal rye, hairy vetch, perennial ryegrass, and a cereal rye-red clover mixture were tried as cover crops. Cereal rye and hairy vetch were fall-seeded, killed with herbicide or mowing in spring, and left as a mulch on the soil surface. Perennial ryegrass was planted as a living mulch with the vegetable crops, while red clover was overseeded as a living mulch on the killed rye a few weeks before vegetable planting. Vegetables were transplanted (cabbage) or direct-seeded (snap bean) in four- to eight-row plots in late May to early June. A conventional-tillage treatment that involved spring disking and pre-plant herbicide incorporation was included as a control.

To date, fall-planted cereal rye has been the most promising mulch system for weed suppression, but improvements are needed to make vegetable yields more competitive with those of conventional tillage systems. Hairy vetch competed with cabbage and decomposed too quickly to provide adequate weed control. Perennial ryegrass was fairly slow growing, limiting early-season weed control. Vegetable yields in perennial ryegrass plots were fair to good for cabbage, but only fair for snap bean. Clover in the clover-rye treatment competed for moisture with the vegetable crops.


Snap beans planted with rye mulch.

Cabbage grown in cereal rye mulch generally had lower numbers of caterpillar pests and aphids than did plants grown in conventional tillage, but insecticide applications were still required. Cabbage diseases were rare in all trials and did not differ among treatments. Snap bean pod damage from chewing insects tended to be least in conventional tillage and greater in plots with mulches, but conventional tillage plots had greater numbers of sap-feeding pests, such as potato leafhoppers, than did mulch treatments. White mold was more common on snap bean pods in conventional tillage than in mulch treatments.

Current research is focused on improving crop yields with cereal rye mulches and in determining the mechanisms that influence pest problems (positively or negatively) in these systems. Planting vegetables into strip-tilled areas within rye mulch plots has improved yields, and large-plot trials planned for 1997 will continue to refine the usefulness of this cover crop option as an alternative production practice for Illinois vegetable growers.

Cathy Eastman, Center for Economic Entomology, in cooperation with John Masiunas and Harry Bottenberg (Department of Natural Resources and Environmental Sciences) and Darin Eastburn (Department of Crop Sciences), University of Illinois

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