Timing corn planting with black cutworm instar development is important for preventing damage to young corn seedlings. Photo credit: Roger Schmidt, University of Wisconsin-Madison, Bugwood.org.
Black cutworm (Agrotis ipsilon (Hufnagel)) can devastate young corn plantings in early spring. Typically, these lepidopteran pests cannot survive the cold temperatures of Pennsylvania winters, but the adult moths migrate northward from the Gulf Coast in late winter and early spring when they lay their eggs on grasses, dense patches of weeds, and field debris. As the larvae emerge, they feed on small crop seedlings at night and can completely cut the plants off at the base. In the daytime, they burrow beneath the soil surface. An earlier Penn State Extension article more thoroughly describes black cutworm characteristics.
It is recommended to scout for cutworms by digging into the soil around damaged seedlings during the day or by searching with a flashlight at night when larvae are most active. Walk fields as plants emerge to monitor for damage. Monitoring adult black cutworm (moths) with pheromone traps is another option that is a less time-consuming method than scouting. Pheromone traps can help monitor target insects and provide information like mating activity and population density. Although the insecticide kill strip in the bottom of the bucket trap could not be used in organic fields, soapy water could be used. In non-organic systems, infestations of black cutworm can sometimes be controlled with soil-incorporated insecticides at planting, but organic rescue treatment options are limited. Some allowable materials do exist for organic producers (provided that the formulation is on the national list of allowed materials and the use is approved by the certifying agent), but these materials are expensive and therefore largely impractical for use on field crops. As a result, organic growers may have to replant field crops when damage is too severe.
Because damage by these insects can be devastating, prevention is the best method for protecting crops against these pests and use of cultural practices is encouraged for both organic and non-organic farms.
Time of planting. Seedlings have the greatest risk of being damaged by black cutworm. The problem can be especially severe when wet springs have delayed planting, because emergence of the crop is more likely to occur at the same time that the large larvae (see figure) are feeding. Seeding at adequately high populations and using practices that promote rapid seedling growth can also be important for allowing resilience to seedling loss.
In central PA, black cutworm have three generations per year. Larvae of the first generation are most damaging to seedlings emerging in June. Because second and third generations are usually more active in July and early autumn, they are usually less of a problem because larvae do not cause extensive damage to large corn plants. However, depending on timing, replanted seedlings might be at risk. Degree day accumulation can be used to predict damage by large larvae that begins at a minimum development threshold of 50°F.
Clean up crop residue. Cutworms are usually found near field borders, in weedy areas, and in cover crop residues. To help reduce the spread of larvae to vulnerable germinating crops and seedlings, weed control programs for fall and spring weeds should be implemented well before planting time. Clean tillage can be used in organic cropping systems to remove weedy vegetation, incorporate cover crop residue, and reduce cutworm larvae and pupae in soil. It is equally important to manage vegetation that hosts larvae along field borders. Black cutworm can also be a problem when corn follows sod or pasture and this rotation sequence should be avoided to help avoid this pest. Further advice is available regarding weed management planning for organic farms.
Biological controls. Cutworm larvae have a number of natural predators including other insects as well as fungi, bacteria, and nematodes in the soil. Even many bird species can prey upon black cutworm. The best approach for balancing multiple organisms across the farm is to practice holistic farm management tactics that act as the basis for ecological pest management, but realize that it might take time to develop. Ecological pest management is based on the use of multiple tactics to manage pets in the agroecosystem rather than a single approach to control them. It includes principles and practices that are already the backbone of most organic farming systems. These practices include those that build soil organic matter and promote soil health, enhance crop diversity, feature crop rotations, use cover crops, and use tolerant and resistant crop varieties. More information is available about individual tactics that adhere to these principles.
References and Additional Reading
Altieri, M.A., C.I. Nicholls and M.A. Fritz. 2005. Manage insects on your farm: A guide to ecological strategies. Sustainable Agriculture Research and Education.
Black Cutworm. 2009. Penn State University Extension.
Creating a weed management plan for your organic farm. 2009.
Cutworms and armyworms. 2017. How to Manage Pests, UC Pest Management Guidelines. Agriculture and Natural Resources, University of California.
How can I organically control cutworms? 2018. ATTRA and NCAT.
Managing insect pests in organically certified corn. North Carolina State Cooperative Extension.