Elisabeth Hodgdon, Extension Associate
Cornell Cooperative Extension, ENYCHP
In recent years, winter cutworm (Noctua pronuba) damage in high tunnel winter greens has been an increasingly widespread problem in the Northeast. While producers are accustomed to dealing with cutworms of various species on the farm, the extreme cold tolerance of winter cutworm takes some growers by surprise. Winter cutworm is the only cutworm that can be found in deep winter crawling on top of snow to find foliage to feed on. These cutworms will feed on lettuce, mustards, spinach, Swiss chard, and other overwintered crops in high tunnels from fall through late winter and early spring before they pupate and emerge as adult moths. While some cutworms clip plants at the base of the stem, winter cutworm feeding looks similar to other foliar caterpillar feeding that results in chew marks and holes in the leaves. Winter cutworm caterpillars (larvae) feed during the night, although they can be found amongst the crop during the day when scouting. In my area (Clinton/Essex Counties), I have seen winter cutworm on high tunnel mustards, spinach, and overwintered cut flowers beginning in October/November, and I just saw caterpillars this week as well.
Researchers are still learning more about winter cutworm and its life cycle in high tunnels to inform management recommendations. At the University of New Hampshire, Dr. Anna Wallingford and her research group found that Bt is effective, and growers report that spinsoad products are effective for winter cutworm larvae. For most effective control, Bt should be applied when the caterpillars are small. Because Bt pesticides contain a toxin that must be ingested, good spray coverage is necessary. Less must be consumed to have an effect on younger, smaller caterpillars. Caterpillars that are sickened by Bt slowly become inactive, lingering on plants during the day and eventually dying. Additionally, there are baits labeled for greenhouse use on leafy greens for cutworms with the active ingredient spinosad. Keep in mind that any pesticide product used in high tunnels in NYS must be labeled for use in greenhouses. Less is known about the efficacy of other insecticide products on winter cutworm specifically because this pest is sporadic and a relatively new threat to vegetables as winter production increases in popularity.
Non-insecticidal strategies for winter cutworm that have interested growers are entomopathogenic nematodes (EPNs) and exclusion. To date, no research has been conducted specifically on EPNS for winter cutworm. Cold temperatures are limiting to EPNs because they are not active when the soil is cold (less than ~50F). Application of EPNs is likely not feasible in the winter, but they could be applied and established earlier in the season or in the spring when temperatures are warmer. More research is needed to better understand how to make use of EPNs for pests like this cutworm that are active in the winter. Additionally, exclusion netting on the sides of high tunnels could exclude moths from laying eggs in tunnels, but there is a significant trade off with disease prevention and beneficial insects. Installing netting on sidewalls of tunnels reduces air flow, increasing humidity in the tunnel and creating conditions that favor disease. It also keeps out natural enemies that predate and parasitize aphids and other high tunnel pests.
If you’re interested in learning more about winter cutworm, you can view the webinar recording on this topic from a panel of presenters from the University of New Hampshire, University of Vermont, and Cornell Cooperative Extension. Dr. Anna Wallingford presented on winter cutworm at the New England Vegetable and Fruit Conference, and her slides are available as an online resource at this link.
A collection of winter cutworm larvae found in overwintered high tunnel cut flowers in November in Essex County. Winter cutworms can be green or brown and have an upside down “Y” on their head. Photo: E. Hodgdon