Time of hilling and interseeding affects weed control and potato yield

Abstract

The current emphasis on reducing pesticide use has led to increased interest in alternative weed control methods. The purpose of this study was to evaluate the potential of hilling, in combination with subsequent interseeding of cover crops, to control weeds in potato and to determine the impact of these actions on potato yield and insects. Each cover crop, either hairy or lana vetch, oats, barley, red clover, or a combination of oats and hairy vetch, was interseeded, following hilling, 3, 4, or 5 wk after planting (WAP). Hilling and interseeding treatments were compared to a no-cover treatment and a chemical standard, metolachlor (1.7 kg ai ha−-1) plus linuron (1.7 kg ai ha−-1). Cultivation associated with the interseeding operation and cover crops reduced weed density 20 to 27% by 3 wk after interseeding. To prevent excessive competition, cereals interseeded 3 or 4 WAP and vetches interseeded 3 WAP were controlled at a height of 25 to 35 cm using fluazifop (0.22 kg ai ha−-1) plus metribuzin (0.28 kg ai ha−-1). Because of slow growth, it was necessary to control red clover (interseeded 3 WAP), only in 1996, at a height of 15 cm. Control of cereals resulted in a dead mulch that provided 0 to 95% weed control, whereas legumes regrew after herbicide application and provided 45 to 70% weed control. However, an adequate minimum of 70% weed control was achieved only with the chemical standard, cereals (1995 and 1996), and legumes (1996) interseeded 3 WAP when controlled with herbicides. In a dry season (1995), potato yields were highest with the chemical standard, whereas in a season with adequate precipitation (1996), potato yields equivalent to those of the chemical standard were obtained with early interseeding (3 WAP) of cereals. The observed changes in the densities of potato leafhopper and of its natural enemies were unlikely to have any effect on potato yield because of low overall insect populations. Thus, the results suggest that in good growing conditions, early (3 WAP) interseeding of cover crops supplemented with postemergence herbicides may both suppress weeds with 70% less herbicide (ai ha−-1) and provide yields comparable to those associated with conventional potato production.