Effect of tillage practices and weed management on survival of stalk borer (Lepidoptera: Noctuidae) eggs and larvae.

Increased use of conservation tillage by midwestern corn growers in the 1970s and 1980s has led to a greater incidence of problems with the stalk borer, Papaipema nebris (Guenee). In particular, serious infestations have occurred throughout entire fields where no-till is practiced. A 3-yr factorial experiment (1983-1986) assessed the effect of three tillage practices (fall moldboard plow and spring disk, fall chisel plow and spring disk, and no-till) at two levels of weed management (weed growth present or absent in spring) on the survival of stalk borer eggs and development of larvae from surviving eggs. Injury to corn was used as a relative measure of stalk borer survival. Egg masses were infested on or immediately adjacent to grassy weeds after harvest but before tillage operations took place. Winter wheat was sowed in the fall to supplement natural weed growth in the plots with no weed control. In plots with the high level of weed control, plant growth was controlled, as needed, with paraquat in spring before planting. In all three studies, the tillage X weed management interaction was not significant and the moldboard-plow treatment significantly decreased stalk borer damage when compared with the no-till treatment. The chisel-plow treatment was generally intermediate between the no-till treatment and the moldboard-plow treatment in reducing stalk borer damage. The absence of weed growth in spring tended to decrease infestations of larvae, although the difference in damage between the two levels of weed management was significant in only one of the study periods. In that period, the interval between predicted 50% stalk borer egg hatch and the one-leaf-stage of corn development was greater than that interval for the other two studies. Even with the burial of eggs by soil with the moldboard-plow treatment, some larvae successfully eclosed and survived to damage corn seedlings in two of the three studies, with or without the presence of weeds. Although the results clearly show that no-tillage planting practices favor the survival of stalk borer eggs and larvae, other studies suggest that stalk borers would be better managed by controlling grassy weeds within fields in the late summer and early fall to prevent oviposition rather than relying on tillage or weed control practices to reduce populations of eggs and larvae after oviposition has already taken place.