Black Cutworm Moths Arriving, and Seedcorn Maggots Making Themselves Known

 

 

Our first significant flight of cutworm moths arrived in PA, and we have encountered an odd situation with seedcorn maggots infesting insecticide-treated seed.

 

As mentioned in our newsletter previously, again this year Penn State Extension and the Department of Entomology are monitoring black cutworm populations with pheromone traps. As moths arrive, if we capture eight or more moths over the course of two nights (a “significant flight”), there is an elevated risk in that particular area of cutting damage by caterpillars later in the spring. States to our west, like Indiana and Illinois, have seen relatively mild flights of black cutworm moths, so the risk of cutting damage appears to be lower than average this season. Consistent with lower activity elsewhere, thus far we have only detected one significant flight of moths across all our traps. The first arrived in Potter County (near Ulysses) late last week. In other parts of the state, we have detected lower numbers of moths, but none that have exceed eight moths over two nights. We continue to trap for others, but will now begin degree-day accumulations to predict the timing of cutting for Potter County to inform folks when they should be scouting fields for damage. For all other parts of Pennsylvania, I recommend regular (every 10 days or so) scouting in all corn fields to detect any cutting by populations of caterpillars from moths that eluded our traps. Rescue treatments are usually the most efficient and economical tactic for managing black cutworm. For more information, see our black cutworm fact sheet.

 

One other pest issue I heard about this week involves seedcorn maggot. Seedcorn maggot is most problematic in tilled fields planted with large-seeded crops like corn, soybeans, and some vegetable crops—they tend to be less of a problem in no-till fields. Because of the widespread use of insecticidal seed treatments in corn and soybeans, seedcorn maggot infestations seem to be somewhat uncommon these days in “conventional” production fields. Nevertheless, yesterday I heard reports from an area over near the Pennsylvania-New Jersey border. I was told about seedcorn maggot infestations in tilled and no-till soybean fields that were planted with seeds coated with neonicotinoid seed coatings—the infestation in the tilled field is causing about 90% stand loss. Because of the generally strong efficacy of neonicotinoids against seedcorn maggot, these infestations took me by surprise. I see two possible explanations. The first is that the maggots could be resistant to the insecticide, but this seems unlikely because seedcorn maggot has 3-5 generations per year (for lifecycle see Figure 1) and maggots would generally only be exposed to active ingredients of neonicotinoids during the first generation, providing only mild selection pressures for evolution of resistance (it would be a different matter if maggots were exposed to the same insecticide each generation). A second possible explanation is that the abundant rain we have received may have washed the insecticide away from the root zone, leaving the seed and seedling unprotected. I think this explanation has some merit because the neonicotinoid insecticides applied to seeds are water soluble and will leach away from the seed and even out of fields with enough rain. I raise the issue here to make people aware of the situation, and take advantage of all the eyes out there on crop fields. If you see a similar situation or can propose an alternative hypothesis, I would like to hear from you.