Black Cutworm in Turfgrass

The black cutworm [(BCW) Agrotis ipsilon, family Noctuidae] is a caterpillar pest of many crops, including turfgrasses. Adults are medium-sized (1.5—1.9 inch) moths with brown wings, held flat against their back at rest. Each forewing is marked by a faint dagger-like marking (Figure 1).

Larvae are generalist grass pests, capable of infesting a variety of turf and crop grasses. Pupae and adults overwinter in warmer southern regions. Each spring, adults migrate north and begin to mate and lay eggs. Eggs are deposited on the petiole or under the leaf surface of grasses or weeds, either singly or in dense clusters. Eggs are white when freshly laid, gradually darkening to gray, brown, and black before hatching. BCW caterpillars are thick-bodied, non-hairy, and typically dark gray to black. They have three true leg pairs attached to their thorax in addition to five pairs of fleshy prolegs on their abdomen. Larvae are nocturnal, emerging at night to feed on leaf surfaces. They return by day to shallow burrows or coring holes. Larvae typically progress through six to seven instars before pupating (Figure 2). Mature larvae pupate in their burrows, emerging as adults that may continue to migrate northward. Ohio has two to three generations per year, while in southern states they can be active longer, with shorter generation times.

Distribution

BCW moths have the widest distribution of any cutworm, with populations found throughout the Americas, Africa, Europe, and Asia. In North America, they overwinter in subtropical regions where the soil remains above freezing temperatures and then they fly northward with spring storm fronts. Annual migratory flights can result in infestations as far north as Southern Canada. First-generation adults tend to fly north from southern states in late April to early May. They then produce a generation of new adults that fly in late June to early July. A third generation of adults can fly from late August to September.

Damage

Early-instar larvae first feed on glass leaf blades for a few days before moving down to the thatch surface where they hide during the day. Late-instar larvae (fourth to sixth instars) feed from burrows or aeration holes just under the ground’s surface, severing plants near ground level. This results in characteristic sunken “pockmark” damage on playing surfaces of low-cut turf (such as greens and tees), often severely impacting playability. Feeding damage happens at night when larvae are most active. Black cutworms are generalist feeders that can damage a variety of cool- and warm-season grasses. Meanwhile, they are significant pests of some field crops including corn, where larvae cause significant damage to young plants. They can find many hosts among the cool-season grasses of Ohio turf, including perennial ryegrass, tall fescue, creeping bentgrass, and many bermudagrass cultivars, though creeping bentgrass is the preferred turf host.

Monitoring/Sampling

Adults of all cutworm species are attracted to blacklight traps, and pheromone traps can be used to monitor individual species. Though adult-trap counts do not always correlate to subsequent damage levels, they can help identify peak flight times and predict the oviposition and larval emergence that follows. A flight event often peaks within a week of the initial trap catches. When a peak is determined, short-residual insecticide treatments are often most effective when applied about two weeks later. Maximum egg laying occurs during the peak adult flights and shortly afterwards. Eggs hatch in a couple of days and the young larvae rarely cause visible damage. Within two to three weeks, the larvae may begin causing visible damage to turf in short-cut areas like golf greens and tees.

Sampling and monitoring of BCW larvae can be easily performed using a disclosing drench or flush. Common dishwashing detergent can be used for this purpose. Generally, two tablespoons of concentrated dishwashing detergent in two gallons of water are sufficient to drench one square yard of turf. By using a watering can to evenly apply the solution over the turf, larvae can be forced to the surface. Some of the small larvae may die near the surface, which can result in underestimates of total populations, but a disclosing drench or flush can still be valuable in determining the size distribution of a population.

BCW management can be augmented via degree-day monitoring techniques with a developmental threshold of 50 degrees Fahrenheit, beginning after the first day of intensive capture of adults. Important accumulation thresholds for BCW development are listed below (Table 1).

Management

Cultural Control

BCW larvae demonstrate clear host preferences despite their generalist diet. BCW larvae in corn fields often only attack young corn plants after the weeds in the field have been depleted. On golf courses, BCW usually target creeping bentgrass and other cool-season grasses before attacking Kentucky bluegrass, which may render some level of resistance to BCW, likely involving a chemical deterrent or toxin that inhibits BCW development. In all susceptible turfgrass cultivars, younger plants tend to be at higher risk of BCW damage compared to mature plants, probably because of differences in nutrient levels. Mowing tee and green surfaces can remove cutworm eggs with the clippings. However, many of the eggs may survive the mowing process and will hatch wherever the clippings are disposed. Therefore, it is recommended to either compost the clippings or move them far away from green or tee surfaces.

Chemical Control

Chemical insecticides (listed in Table 2) can be used for controlling BCW larvae, and smaller, younger stages are usually more susceptible. Numerous laboratory experiments concluded that BCW larvae are most susceptible to pyrethroid insecticides, more resistant to organophosphate chemicals, and highly resistant to carbamate compounds. Specifically, pyrethroid insecticides with active ingredients such as deltamethrin, lambda-cyhalothrin, bifenthrin, and cypermethrin are highly lethal towards BCW larvae. Additionally, anthranilic diamides and a few neonicotinoids (clothianidin and dinotefuran) can provide effective caterpillar control.

Based on the chemical group and mode of action, different products may have different activities and residual periods. Pyrethroids take effect- through direct contact or ingestion by the target insects and have short residuals that require them to be applied when caterpillars are active. For optimal efficacy, sprayed pyrethroids should be allowed to remain on the turf surface without irrigation for at least 24 hours. Granular applications will need irrigation to move the chemicals into the surrounding area where pests are active. On the other hand, anthranilic diamides can be applied in a preventive manner 2–3 months prior to potential damage and can be watered after application. A treated buffer zone of approximately 20–30 feet (6–9 meters) should be created around treated greens to prevent nearby BCW larvae from crawling into greens after insecticide activity has stopped.

Biological Control

Biological control can serve as an alternative to chemical control. Commercial formulations of entomopathogenic nematodes have proven to be effective at controlling larval BCW, with Steinernema carpocapsae exhibiting the highest control performance.

Endophytic fungi that naturally exist in some turfgrass types, such as tall fescue and perennial ryegrass, are shown to have poor efficacy against BCW. Unlike some other surface-feeding pests that are highly susceptible to endophyte toxins, BCW larvae are rarely impacted. In fact, experiments suggest that BCW larvae can utilize the toxins from some common endophytes to repel or suppress entomopathogenic nematodes that could (or already have) infected them. To the contrary, the white muscardine fungus Beauveria bassiana, which is naturally-occurring and commercially-available, has shown efficacy against BCW larvae and is one of the most effective entomopathogenic fungi available for controlling BCW.

Bacillus thuringiensis subsp. kurstaki and aizawai are important biorational products for controlling a wide variety of lepidopteran pests, though their efficacy is limited for controlling BCW populations—especially later-instar larvae. Applying treatments early in larval development (around the first or second instar) results in the highest effectiveness.

Another natural pathogen, a baculovirus (AgipMNPV), has been identified as a promising control agent in targeting developing larvae, though repeated applications may be required to achieve season-long control as it has poor residual activity. Despite its brief residual activity, AgipMNPV can be highly effective against newly hatched larvae but its efficacy decreases sharply for larvae beyond the third or fourth instar. This makes it best suited for application following peak flight events. Therefore, this tactic pairs well with pheromone traps.

Natural enemies play an important part in the regulation of wild BCW populations. BCW larvae are targeted by a variety of predatory beetles and ants, as well as parasitoid wasps and flies. Use of pollinator gardens or conservation strips may increase populations of these natural biological control agents, which can prey upon other pests as well.

Disclaimer: Pesticide recommendations are subject to change with time and are provided only as a guide. It is the pesticide applicator’s responsibility, by law, to read and follow current label instructions for the specific pesticide being used. No endorsement is intended for products mentioned, nor is criticism meant for products not mentioned. The author and Ohio State University Extension assume no liability resulting from the use of these recommendations.

Additional Resources

• The potency of chemical insecticides in management of cutworm, Agrotis ipsilon Hufnagel (Noctuidae: Lepidoptera): A review.
  (entomoljournal.com/archives/?year=2020&vol=8&issue=3&ArticleId=6765)
• Destructive turfgrass insects: biology, diagnosis, and control.
  (wiley.com/en-us/Destructive+Turfgrass+Insects%3A+Biology%2C+Diagnosis%2C+and+Control-p-9781575040233)
• Turfgrass insects of the United States and Canada.
  (cornellpress.cornell.edu/book/9781501747953/turfgrass-insects-of-the-united-states-and-canada)