CROP BORDERS REDUCE POTATO-VIRUS-Y INCIDENCE IN SEED POTATO

Crop borders of soybean (Glycine max), sorghum (Sorghum bicolor), wint er wheat (Triticum aestivum) and potato (Solanum tuberosum) were teste d as a means of reducing potato virus Y (PVY) incidence in seed potato . Borders of fallow cultivated ground served as controls. Aphid landin g rates were monitored weekly in plots using green tile traps, and PW incidence was assessed by serologically testing tuber progeny from sel ected rows in each plot. Average weekly aphid landing rates in fallow- bordered and crop-bordered plots were not significantly different in 1 992 (29.4 and 25.2 aphids, respectively) or 1993 (7.3 and 6.6 aphids, respectively). However, crop borders significantly reduced PW incidenc e. In 1992, fallow-bordered and soybean-bordered plots averaged 47.8% and 35.0% PVY infection, respectively. In 1993, PVY infection averaged across all crop (soybean, sorghum, and wheat) bordered plots was 2.7% compared to 6.8% in fallow-bordered plots. PW incidence in the centre rows of fallow-bordered and crop-bordered plots was statistically equ ivalent, while outer rows of crop-bordered plots had significantly les s PW than outer rows of fallow-bordered plots. Crop borders apparently reduced the number of viruliferous aphids landing on the edge of the plot. The choice of crop species used as a border, or treating the bor der with a systemic insecticide, did not affect aphid landing rates or PW incidence. In 1995, PW incidence in the centre 10 row block of pot atoes averaged 2.1% across all crop borders (potato and soybean). PVY infection in the four row potato border averaged 5.7%. Crop borders ar e readily adaptable to current production practices, although the grea test benefits in reducing PVY incidence would occur in average sized, generation 0 (< 0.2 ha), elite seed potato fields.