If you are seeing unexplained defoliation in your tunnel vegetables, now might be the time to venture out with your headlamp after dark. You might just catch one of these night-feeding caterpillars in the act!
There are several species of pest caterpillars that might be dwelling in tunnel soils this time of year. Control tactics will be more or less the same, but species may vary in their life cycle and their cold tolerance, which will influence whether or not your fall infestation will remain in your tunnel until springtime.
Winter cutworm (Noctua pronuba) and Yellow-striped armyworm (Spodoptera ornithogalli) are both known to cause foliar feeding injury like that seen in the above photo. Winter cutworm gets its name due to its remarkable cold tolerance, famously found crawling over snow in the dead of winter. Younger winter cutworm can look very different than the older stages, bright green in color compared to dark brown with distinctive dashes. Both winter cutworm and yellow-striped armyworm have a yellow-stripe along their body, but winter cutworm has a brown head capsule while the yellow-striped armyworm has a black head capsule.
Winter cutworm (Noctua pronuba)
Photo credit: Becky Sideman
Variegated cutworm (Peridroma saucia) and black cutworm (Agrotis ipsilon) are also common to the northeast but are more likely to cause feeding damage at the soil surface than feed on the leaf margin – often “cutting” the whole plant off right at the base. While these species are not known to overwinter in the northeast with much success, we suspect that high tunnels provide enough protection from the elements to allow for better-than-average overwintering conditions.
There are very few chemical control options for controlling soil-dwelling arthropods, such as these caterpillars. Depending on the level of infestation, handpicking these caterpillars is a viable option (bring a bucket of soapy water in which to fling those caterpillars). While Bt products (e.g. Dipel) are often an effective biological control for plant-feeding caterpillars, these products are most effective on younger stages so early intervention is best. While understudied in this system, entomopathogenic nematodes (EPNs) might be an option for biological control of soil-dwelling caterpillars. More information on EPNs and their application here.
Pest Alert: Night-Feeding Caterpillars in Tunnel Vegetables is written by sff1008 for extension.unh.edu