Time of hilling and interseeding affects weed control and potato yield

The current emphasis on reducing pesticide use has led to increased interes t in alternative weed control methods. The purpose of this study was to eva luate 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 v etch, was interseeded, following hilling, 3, 4, or 5 wk after planting (WAP ). Hilling and interseeding treatments were compared to a no-cover treatmen t 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 p revent excessive competition, cereals interseeded 3 or 4 WAP and vetches in terseeded 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 gr owth, it was necessary to control red clover (interseeded 3 WAP), only in 1 996, at a height of 15 cm. Control of cereals resulted in a dead mulch chat provided 0 to 95% weed control, whereas legumes regrew after herbicide app lication 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 h erbicides. In a dry season (1995), potato yields were highest with the chem ical standard, whereas in a season with adequate precipitation (1996), pota to yields equivalent to those of the chemical standard were obtained with e arly 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) interseedin g of cover crops supplemented with postemergence herbicides may both suppre ss weeds with 70% less herbicide (ai ha(-1)) and provide yields comparable to those associated with conventional potato production.