INTERACTIONS AMONG THE SOYBEAN LOOPER (LEPIDOPTERA, NOCTUIDAE), THREECORNERED ALFALFA HOPPER (HOMOPTERA-MEMBRACIDAE), STEM CANKER, AND RED CROWN ROT IN SOYBEAN

Field experiments in 1988-1990 determined the (1) effects of defoliati on by Pseudoplusia includens (Walker) (soybean looper) or basal stem g irdling by Spissistilus festinus (Say) (threecornered alfalfa hopper) on soybean stem canker severity and (2) effects of the soybean looper defoliation on red crown rot incidence. Compared to ungirdled plants, stem canker severity was increased while stem length, stem diameter, a nd yield were reduced for girdled plants. Stem canker severity, number of perithecia, yield, stem length, and stem diameter were reduced on defoliated soybean, compared to undefoliated soybean. Red crown rot in cidence, perithecial production, and yields were reduced on defoliated soybean compared to undefoliated soybean. This suggests different typ es of insect injury may either increase or decrease the severity of so ybean diseases.