Plasticulture production of vegetables has been widely adopted in the Northeast providing farmers with in-row weed control, soil moisture regulation and season extension. However, the bare row middles in this system require herbicide or cultivation which increase environmental impacts; impairing water quality, decreasing soil organic matter levels and increasing labor inputs. In 2012 the Cornell Vegetable Program was awarded a NESARE grant to evaluate a new use of cover crops, by sowing winter rye between plastic-mulched beds of tomatoes and onions on two cooperating farms. Both farms provided cultivation and herbicide treatments to enable us to compare weed control, yield and pest and disease impacts.

Results and Discussion
Rye as an inter-row cover crop presented challenges in this project. The primary effect observed was loss of yield, as measured by fresh weight of product. In tomatoes we lost over 8.5 pounds of marketable fruit per plant, a value of nearly $13/plant, assuming an average price of $1.50/lb, compared to the herbicide treatment. In onions the loss was over 18 lbs per 10 linear feet of row when compared to cultivation, the highest yielding treatment. Calculating onion economics is difficult as there are price differentials related to grade (bulb size) and market. However, rye treated plots yielded less than half than number of colossal bulbs (> 4" diameter) of herbicide and cultivation plots. The value of these bulbs is often $ 0.40 more than the next class, representing a loss of over $21 per 10 linear feet of bed.

What is causing this yield loss is not completely understood. Mid-summer rainfall at both farms was scarce, and thus water competition is a possibility. Nutrient competition is also possible, with nitrogen and potassium at times lower in the rye plots, although trends are not clear. Allelopathy from the rye has also been suggested, even though rye roots did not extend underneath the plastic mulch when examined. Pest pressure in the tomato crop did negatively affect yield as common armyworm and slug feeding lead to many unmarketable fruit. The armyworm infestation was a regional phenomenon at abnormally high levels in 2012.

Rye provided very good weed control at both farms. At our onion site it performed as well or better than herbicides and cultivation until harvest. At our tomato site late season weed pressure increased in the rye plots. There was an unexpected disease in the rye, leaf rust, caused by Puccinia recondita tritici at both sites. Although this disease did not impact the vegetable crop it reduced rye stands.

For more information on this project design, results, and conclusions, download the full report below.