By John Tooker
Western bean cutworm moths are active in Pennsylvania corn fields laying their eggs so it would be wise to scout fields for eggs and young caterpillars to understand the threat that this pest species poses to your fields. For the first time in seven years, Penn State Extension and the Department of Entomology are monitoring western bean cutworm moths with pheromone traps to understand the population dynamics of this species, which we first found in Pennsylvania in 2009. In the past week, our traps have yielded from zero to almost 300 moths per week, so the populations are unevenly distributed across the state. The highest numbers found were in Centre County, so growers in this region should prioritize scouting and look for eggs and young caterpillars in tassels and silks. High number of moths were also captured in Indiana, Ohio, and Ontario, so we are recommending that growers across Pennsylvania scout their fields for eggs and larvae to understand the risk from this pest species. Look for egg masses on the upper leaves of corn (Figure 1) and young caterpillars feeding on reproductive tissue, including pollen in whorls, the tassel, or in the silks; the caterpillar eventually will find their way to the developing ear.
You should be aware that corn hybrids with the Herculex 1 trait (i.e., the Cry1F protein) can help suppress populations of this caterpillar, but often do not provide adequate levels of protection. The main Bt trait that can help control western bean cutworm is the Agrisure Viptera (Vip3A) trait. (See this resource from Michigan State and Texas A&M to understand what protection your hybrids offer against western bean cutworm.) A generally accepted economic threshold for western bean cutworm is 5% of plants having eggs or larvae, so corn grain and silage fields above this level would benefit from an insecticide application. Of course, the timing of this application is key because it needs to occur after eggs hatch but before caterpillars enter ears and are protected from insecticides by husks. Fields that do not have populations that exceed the economic threshold are unlikely to benefit from insecticides and may actually suffer if the insecticide flares aphid populations, which grow in the absence of natural enemies. Young western bean cutworm caterpillars have black heads and yellow, spiny-looking bodies (Figure 2). Later in the season, more mature western bean caterpillars look similar to corn earworm but do not have lines down the sides of its body like corn earworm does and has three distinct light-brown lines on its "neck" just behind its head.
Source : psu.edu