Now that Spring has arrived in earnest, various pest species are active and they should be kept in mind. These pests include alfalfa weevil, timothy mites, cereal leaf beetle, black cutworms, and slugs, and we have addressed all these pest species in our newsletter in recent weeks. The latter two species tend to be perennial concerns, and for that reason we pay closer attention to them.
As we have shared in recent weeks, Penn State Extension and the Department of Entomology are again using pheromone traps to monitor for arrival of black cutworm moths across Pennsylvania. For the most part, our traps are only detecting small numbers of moths; we have not detected populations of moths that are very concerning, but we will continue to monitor and will share with you what we find. If we detect significant flights of moths, we will use degree-day accumulations to predict when their cutting damage in corn will be likely to occur.
As a reminder, black cutworm caterpillars are best managed with Integrated Pest Management, which in this case means with a combination of scouting and rescue treatments if populations exceed economic thresholds. (The economic thresholds are 2, 3, 5, and 7 cut plants per 100 seedlings for seedling, V2, V3, and V4 stage plants, respectively.) Rescue treatments, not preventative sprays remain the most efficient and economical tactic for managing black cutworm. For more information, see our factsheet.
As for slugs, they are becoming active, particularly in no-till fields, with juveniles hatching from eggs. In areas that have received rain recently, or in fields that tend to lie wet, these happy slugs may cause damage as corn and soybeans emerge. We have a factsheet that describes scouting and management options, but in our experience, managing slugs takes an integrated approach that should be planned well before spring plantings.
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Nevertheless, for growers who see an impending problem from healthy slug populations, it might be useful to consider delaying planting until soil temperatures are warm enough for corn or soy to jump out of the ground when it is planted. Nothing exacerbates slug problems like a crop that is slow to emerge and lethargic given cool temperatures.
It is useful to keep in mind that our research has demonstrated that strong populations of ground beetles can help suppress slug populations. Populations of these beetles tend to be suppressed by insecticide use, including seeds treated with neonicotinoid insecticides, so consider avoiding insecticide-treated seed if you have fields that are perennially damaged by slugs. To prepare for potential slug damage, it can also be helpful to have some slug bait on hand to use as rescue treatments in portions of fields being damaged.