Figure 1. A corn plant near Christiana, PA, recently cut by a black cutworm caterpillar (image by Tracy Neff, Kings Agriseed)
Pest activity is starting to pick up across the state, and several pests warrant attention as you scout your field and forage crops. First, as mentioned in previous weeks, our Black Cutworm Trapping Network detected only one significant flight of moths, which occurred in Potter County near Ulysses. The degree-day accumulation for this area sits at 265, and we expect cutting to be evident in corn fields at 300 degree days, which we could reach by Friday or Saturday. Folks in that part of the world should plan to scout their fields for cutworm damage toward the end of the week, looking for cut plants (Fig. 1). In newly emerged corn fields, also keep an eye out for damage from young caterpillars to young plants (Fig. 2). In other parts of the state, there is a general risk for cutting damage, and folks need to scout their fields to find this damage to determine if chemical treatment is warranted. Widely accepted economic thresholds are 2, 3, 5, and 7 cut plants per 100 for seedling, V2, V3, and V4 stage plants, respectively. For stages V5 and onward, black cutworm are seldom economic problems. For more details on black cutworm, please visit our Black Cutworm factsheet .
Figure 2. A young corn plant with leaf-feeding damage from a young black cutworm caterpillar. Photo credit: Nicole Carutis, Penn State Extension
Second, potato leafhopper has arrived in the state and populations in some areas are building. Growers would be wise to keep an eye out for increasing populations of this pest because once their feeding is evident economic damage has been done. Potato leafhoppers are perennially the most damaging pest of alfalfa in Pennsylvania. Their feeding reduces yield and quality (especially lower protein content) and can decrease stand longevity. If damaging populations develop, early harvest or insecticides are often the only choices. Early harvest can stop damage, but regrowth should also be scouted to determine if the next cutting also develops damaging populations. To target leafhoppers most effectively, populations should be sampled and treatment applied only when economic thresholds are exceeded. In my experience, regular scouting and use of economic threshold can limit the need to insecticides to once a summer. Scouting details and economic thresholds can be found in our potato leafhopper fact sheet .
Third, as soybeans emerge from the ground, bean leaf beetle populations tend to colonize the earliest emerging fields. If you think your soybean fields are among the first up in an area, be sure to scout them for bean leaf beetle chewing damage. Insecticidal seed treatments tend to be effective against this early season pest, but soybean seedling can still experience defoliation and damage to the cotyledons. Growers may be uncomfortable with damage they are seeing, but beans typically recover well and there is rarely a yield drag from this early season damage. So unless damage it is extreme, be patient and trust your beans.
Lastly, we have received a good number of reports of cereal leaf beetle activity in wheat and oats around Pennsylvania. This time of year cereal leaf beetle infestations are often diagnosed from the cab of a vehicle as fields turn frosted and frosted fields are too late to save. Once populations reach one or more larvae per stem, treatment is typically warranted, especially if larvae are feeding on the flag leaf prior to head emergence. Damage later in head filling does not appear to be significant and if adults are seen late in spring, it is likely too late to manage this pest. For details on this pest’s life cycle and management options, see our recently revised Cereal Leaf Beetle fact sheet .