Effects of systemic insecticides on potato growth and their interaction with metribuzin

Effects of the soil systemic insecticides aldicarb, phorate, and disulfoton on potato growth were measured from 1984–1986 on the cultivars Russet Burbank and Centennial. In all seasons, aldicarb was observed to cause a significant promotion of flowering and in one season also caused increased haulm growth. Phorate caused a reduction in these growth parameters in one season. Temporary effects on early season yields were observed from the aldicarb treatment in one year but final yields were never significantly affected by insecticide use alone. During 1985–1986 additional treatments were investigated involving insecticide combinations with the herbicide metribuzin to determine possible insecticide-herbicide interactions. Phorate-metribuzin combinations caused synergistic metribuzin injury symptoms, decreased haulm growth and yield in 1986. Metribuzin also decreased yields of aldicarb treated potatoes in 1986 and disulfoton treated potatoes in 1985. Disulfoton-metribuzin combinations decreased flowering in 1985. These data suggest that soil systemic insecticides can have direct effects on potato growth, independent of effects on pest suppression, and that they may interact with other crop protection chemicals.