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A common caterpillar we include in our ISU field guides is hop vine borer (Figure 1), but I can’t even remember the last time I saw one. I’m wondering if it’s an early-season pest of the past? Archived ICM News articles tell me it was most commonly observed in northeastern Iowa and states to the east. It was considered an occasional pest that caused stand loss in corn, particularly in fields with grassy weeds. Have you seen it lately?
Description: The adult is a dull brown Noctuid moth (Figure 2), with buff-colored forewings and a wingspan of 1.5 inches. Larvae (or caterpillars) are solid orange or a dark red head. The body is dirty white with dark purple square spots.
Biology: The life cycle is similar to common stalk borer, in that there is just once generation per year and they can overwinter in Iowa. Egg hatch is in late April or early May. Young larvae move to grass stems, like smooth brome, quackgrass, orchard grass, and woolly cupgrass. Eventually, larvae get too big for those grass stems, so they move to larger plants, like corn.
Feeding injury: Hop vine borers attack corn plants from underground, tunnel up and hollow out plants at the base (Figure 3). Their injury to corn plants is unlike other early-season caterpillars, such as: common stalk borer (tunnel aboveground), black cutworm (cut plants aboveground), or armyworm (defoliate corn leaves). Infested plants look stunted, discolored, wilted or the central whorl could die in younger plants. Like common stalk borer, hop vine borer injury is most commonly seen at field margins, or along fence rows and waterways. Repeated injury over several growing season is most likely to be infested in fields with abundant grass.
Management: Scouting hop vine borers should start when corn emerges. Use an insecticide that includes cutworms on the label. Consider targeting applications to the field perimeter to reduce costs. A foliar application is only effective when caterpillars are moving from grass to corn. Insecticidal seed treatments and transgenic Bt traits in corn are not labeled for hop vine borer. Sustainable practices include mowing grasses around cornfields to minimize overwintering success.