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Onion growers see beneficial effects of sudangrass

Sudangrass is a warm-season cover crop with extremely useful qualities: it builds and repairs soil damaged by compaction and depleted by overcropping, and it apparently suppresses harmful nematodes and root rot fungi. But New York's vegetable growers have until now lacked adequate information about how to get the most out of a rotation with sudangrass. For instance, when should it be planted? When and how often should it be mowed?

Three years of demonstrations by Cornell Cooperative Extension educators were concluded in 1996, with sudangrass used as a season-long rotational crop for onions in muck soil. When yield and weight of the onions in the year prior to sudangrass rotation were compared to yield and weight in the year after it, growers saw increases of 29 percent and 15 percent, respectively. Results are likely to be even more positive in years with better weather conditions than those of 1996.

Previous studies have shown that sudangrass reduces pest pressure by breaking pest cycles and reducing populations of soil-dwelling pests. No significant reductions in pest populations were seen in 1996.

While it is unclear at this point whether the improvements in onion yield and quality that follow a rotation to sudangrass are attributable to improved physical characteristics of the soil, suppression of pests, or both, growers appreciate the improvements. They also appreciate the potential for reduced chemical pesticide use represented by such rotation. An average season-long pesticide load on an acre of onions in Orange County is 25 pounds. An acre of sudangrass, on the other hand, requires no pesticides. By planting 280 acres in sudangrass in 1996, Orange County onion growers reduced the countywide pesticide usage by 7,000 pounds (280 x 25).

One of the largest onion farms in Orange County has begun planting sudangrass on 25 percent of its acreage each year. The grower will see to it that each field has been rotated to sudangrass within four years. Eight other growers have also incorporated sudangrass into their production practices during the course of this sudangrass project.

Vegetable growers and agribusinesses have received a fact sheet summarizing cultural practices for sudangrass and data on yield and quality improvements attributable to it. The fact sheet includes the recommendations shown in abbreviated form in figure 1. These tips will become a part of the official Cornell recommendations for onions this year.