Inclement Weather and Black Cutworm

Overall this spring has been difficult on farmers to say the least. The inclement weather this spring permitted most farmers from turning dirt into late June. Not only do the farmers have to combat with the weather this year, but the insect pressures are causing even more issues in the field. Many growers have reported black cutworm present in corn fields across the northeast. While the degree of impact has varied, the presence of cutworms is undeniable.

Black cutworm is a migratory broadleaf lepidopteran that poses a large economic threat. With the capability of producing three generations per year, overwintering in the southern states and migrating north in early spring. This causes their heaviest infestation to be around April and May.

Newly hatched larvae of the black cutworm are around a quarter inch in length and can grow to be about two inches. Their coloring is mostly black but can range to a slight gray with a pale stripe down their backs. The adult moths are pale with a very distinct black dagger shape marking. An irregular white band may be seen on their wings just below their dagger-like markings.

The adult moths migrate north and lay their eggs in patches of weeds or standing grasses. When the eggs hatch, before crop planting, is when higher occurrence is seen in the field. This spring, many fields were too wet to get on to plow or spray before the eggs were laid and hatched. This allowed the eggs to hatch and the larvae to move into the soil. Many of the fields that have seen significant damage this spring were fields that had weeds present in them well into June. As well as those that have very grassy edges that did not get mowed or managed early like other years. For those who were able to keep fields relatively clean and weed-free, the cutworm pressure has been much less.

The damage caused by the cutworm larvae is dependent on the weather and moisture conditions. They exhibit two types of feeding habits; when the soils are lacking adequate moisture, the larvae will remain in the soil and exhibit chewing of the plant below the soil surface; and when the soil has plenty of moisture they will remain in the soil during the day but begin to emerge and feed on the above ground parts of the plants in the evening. Examples of cutworm damage are plants that are chewed off at the soil surface, leaves that may be chewed off or show holes through the leaves, and some plants may be chewed below ground before emerging from the soil.

When scouting for black cutworm, it is important to dig around in the soil. They can be found near the base of plants that show damage and not too deep under the soil. One thing to keep in mind when scouting is the growing point of the corn plant. If the damage is done above the grow- ing point of the plant, that plant will most likely grow back and a replant situation may not be needed. However, plants that have been damaged at growing points or

have been chewed/cut below the growing point will most likely not survive. When considering replanting, it is critical to evaluate where on the plant the majority of damage is being seen so you don’t replant where it isn’t needed. Remember there may be different stages of larvae in the field. When digging up the cutworm it is important to note the stage and growth of the larvae to determine how far along in their life cycle they are and how much more damage they may cause.

Spring 2019 has been an unforgiving one to many farmers. It is especially important to keep the plants that did get planted, healthy and growing so we have a crop to harvest in the fall. If you have any questions or concerns about cutworm damage or any pest pressures please get in contact with your agronomist to tackle the issues before they devastate your fields.

Cassidy Fletcher, Northeast Sales Agronomist and Technical Lead