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The Usual Suspects for this Time of Year: Black Cutworm and Slugs

Posted: May 10, 2017

As spring progresses slowly, the normal line-up of pests are active and should be kept in mind, but two pests in particular seem to be on peoples’ minds.

Black cutworm

Black cutworm moths appear to be more active than normal, which may lead to more cutting damage in corn fields. We have already heard from a grower in Lebanon County who planted in early April and has at least one field suffering from cutting damage. This gentleman wants to know if he should spray the rest of his corn acres for black cutworm because this one is infested, and my response is NO. Unfortunately for this grower, this problem stems in part from planting so early. With most fields not yet even planted, the risk from early-arriving cutworms is usually low and the main concern should usually lie with caterpillars better aligned with the timing of the majority of corn.

Even if there is a somewhat heightened the risk from cutworms this spring, I will continue to recommend that growers stick to an Integrated-Pest-Management approach and scout for cutting damage and apply an insecticide only if the number of cut plants exceeds economic thresholds (economic thresholds are 2, 3, 5, and 7 cut plants per 100 seedlings for seedling, V2, V3, and V4 stage plants, respectively.) As reported last week, we have detected several significant flights of moths in central and southeastern PA. In coming weeks, we will report degree-day accumulations to predict the timing of cutting by larvae to inform folks when they should be scouting fields for damage. Rescue treatments remain the most efficient and economical tactic for managing black cutworm. For more information, see our factsheet on black cutworm.

Slugs

And then of course there are slugs in no-till fields. Juvenile slug have hatched out of their eggs and some populations are making cover crops disappear. In areas that have received lots of rain, or in fields that tend to lie wet, these happy slugs are likely to cause damage as corn and soybeans emerge. We have a slug 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. 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 soybeans 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 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.

Contact Information

tooker@psu.edu