- Scientific Name: Agrotis ipsilon (Hufnagel)
- Common Names: black cutworm, dark sword-grass moth, greasy cutworm, ypsiloneule, Gusano cortador grasiento, Noctuelle ipsilon, Nottua ipsilon o Nottua dei seminati, Nóctua ípsilon
- Climatic Zone: subtropical and seasonal temperate (can fly into temporate zones during spring and summer seasons)
- Geographic Distribution: The black cutworm is found around the world including North and South America, Europe, Japan, New Zealand, South Africa, and many Pacific Islands. The black cutworm is a major small grains crop pest and it is actually a semitropical species. In North America it flies from the Gulf States each spring into cool season turf areas. In the Gulf States, black cutworm can be active year round, but definitely slows its development when daytime temperatures rarely exceed 60 to 70 degrees during the daytime.
- Damaging Stage: larva
- Hosts: all grasses and small grain crops
- Damage Symptoms: Cutworms are so named because of their generalized nocturnal feeding habit of cutting off plants close to the ground. However, on golf course greens and tees, black cutworms graze on grass blades of short cut turf. This causes circular or finger-shaped sunken marks, often called “pock marks.” Cutworm larvae often take advantage of aerification holes where they produce round pock marks that can resemble ball marks on a green. Visible damage in higher cut turf is rare and a general thinning or persistent bird feeding may be the only signs of black cutworm presence.
- Description of Stages: Black cutworms are the larvae of moths and thus have complete life cycles with egg, larval (caterpillar), pupal and adult stages.
Eggs: The eggs are usually round, 2/64 inch (0.5 to 0.6 mm) in diameter, flat on the lower surface and bluntly pointed at the top. No surface sculpturing is evident. Black cutworm eggs are attached, individually or in small numbers, to the tip ends of grass blades. Eggs are first a light green but become tan to dark brown before hatching.
Larvae: The larvae have generally hairless bodies except for a few scattered bristles. The general body color is a dark olive green to a nearly gray-black with a broad lighter colored strip running down the back, and the body has scattered black spots. Under a dissecting microscope, the surface of the exoskeleton looks like a cobblestone surface, which is diagnostic. There are usually six larval instars with mature larvae reaching 1 3/16 to 1 3/4 inch (30 - 45 mm) long and 1/4 inch (7 mm) wide.
Pupae: The pupae are brown, reddish-brown or black and 1/2 to 7/8 inch (13 to 22 mm) long. The antennae, wing pads and legs are firmly joined together, but the abdomen is free to twist around if the pupa is disturbed.
Adults: The adults are generally mottled black and gray-brown with a diagnostic black daggar mark on the outer third tip of the wing. The forewings span of 1-3/8 to 1-3/4 inch (35 to 45 mm). At rest, the wings are folded flat over the abdomen. Male moths have feather-shaped antennae while the female antennae appear as a fuzzy thread.
- Life Cycle and Habits:
In North America, the black cutworm overwinters as larvae or pupae only in the southern states. In early spring, adult moths regularly migrates into the northern states. In the northern states, this pest may have two to four generations per year while in the southern states, five to six generations are possible depending upon the length of the season. Cutworm adults emerge from pupae formed in the soil. They usually mate within the first several nights after emerging, and the adults feed at night from the flowers of trees, shrubs and weeds. Mated females seek crops or grasses to lay eggs. In turf, they attach single or small clusters of eggs to the tips of leaf blades. Each female has the capacity to lay 800 to 1200 eggs over five to ten days. Under optimum conditions, these eggs hatch in 3 to 6 days. First and second instar larvae appear to feed within a leaf blade fold or where the leaf base meets the stem. By the third instar, the larvae move to the thatch but they emerge at night to feed on green leaf tissues. In the forth instar, larval behavior changes considerably. These larvae excavate a hole into the thatch and ground and may line it with silk. From this retreat, the larva ventures forth at night to feed on plant material. At this time the larvae are also cannibalistic. The last two instars, fifth and sixth, continue building burrows, but they may move every few nights to dig a new burrow. In high cut turf, they often drag a leaf or stem back to their burrow to feed on during the daytime. On short cut greens and tees, the larvae simply eat the green leaves down to the ground. Larger black cutworm larvae are known to move considerable distances (often more than 50 feet in one night). They apparently build new burrows every few nights. Most of cutworms take 20 to 40 days to complete their larval development during summer temperatures. The pupae may be located in the cutworm retreat in the soil or in the thatch. The pupa takes about two weeks to mature. Just before adult emergence, the pupa often wriggles to the surface. This action is highly attractive to black birds, especially starlings. Developmental times may be greatly lengthened during the cooler parts of the season.
- Control Approaches: Black cutworms are usually controlled by using one of the contact or stomach insecticides, though biological controls are available. Turf managers have often associated persistent bird feeding in turf with the presence of black cutworms, but research has shown that birds may be feeding on sod webworms or other insects. To ensure that you are dealing with a black cutworm infestation, use a soap disclosing solution to determine actual populations.
Cultural Control - Use Resistant Turfgrasses - Perennial ryegrasses and fescues that contain endophytes are known to slow development or are toxic to armyworm and fall armyworm larvae. However, black cutworm larvae are NOT affected by the endophyte toxins. On the other hand, black cutworm larvae grow slowly or are killed when fed a pure diet of Kentucky bluegrass. Some cultivars of zoysiagrass and bermudagrass are also known that are relatively resistant to black cutworm attack. Check cultivars before selecting them for use.
Natural Control - Diseases, Predators and Parasites - There are numerous bacterial and fungal diseases that are known to attack cutworms. Common predators include ground beetles, rove beetles, ants and birds. Many parasitic wasps and flies attack the eggs, larvae and pupae. These natural controls appear to have a significant affect on cutworms in turf, but their action is often too late to prohibit visible damage.
Biological Control - Entomopathogenic Nematodes - Products containing the insect parasitic nematodes, Steinernema carpocapsae and S. feltiae, are available and effectively control cutworms. Close attention to label recommendations, especially pre- and posttreatment irrigation and soil moisture requirements, is essential for success. A regular program of applications, beginning when the first eggs begin hatching and continuing at a 14 to 21 day interval, thereafter, has been shown to be successful. Affected cutworms die in their burrows, not on the turf surface.
Biological Control - Use BT - Products containing the toxin derived from the bacterium, Bacillus thruingiensis (BT), are commercially available and some new strains appear to affect black cutworm, especially if enough material is ingested by young larvae. Use of these products has had mixed results in turfgrass management because treatments are usually applied to a population consisting of large and small caterpillars. Use of this microbial toxin is best when the caterpillars are in the first to third instars. Irrigation should be omitted for at least 12 to 24 hours after application. Affected caterpillars rarely surface.
Chemical Control - Insecticides - The principle of controlling grass eating caterpillars with insecticides is to apply the treatment to the turf and omit irrigation for 12 to 24 hours until the insect consumes the foliage and makes contact with the treated surfaces. Both preventive and curative approaches can be successful. Monitoring to determine population level and size of larvae before treatment and after a treatment is recommended. Keep in mind that young larvae are far more susceptible to insecticides and other forms of control than are larger larvae.
Curative Treatments. Numerous contact and stomach insecticides in various chemical categories effectively control cutworms in turf. On golf course greens and tees, it is recommended that spraying the area of turf surrounding the affected area (a minimum of one boom or spreader width or 15 to 20 feet) will help keep larvae from moving back onto the greens from surrounding turf.
Preventive Treatments. Some newer, long residual systemic insecticides have shown that application to golf course greens or tees in early May, provided suppression of black cutworm until, at least, late June.
Regular monitoring of turf areas for evidence of cutworm infestation and applying treatment only when larvae are present and/or damage seems eminent, is part of the control process. Monitoring includes looking for larvae, damage and/or evidence of birds (starlings) probing the turf for larvae. To determine if larvae are actually present, an effective monitoring method is to use a solution of liquid soap and water (two tablespoons of liquid Joy® dishwashing detergent in two gallons of water) spread over a one square yard area to flush larvae to the surface. When using preventive biological or insecticide strategies, sample every 14 to 21 days to detect early stage caterpillars, before significant damage is evident.
Determination of whether treatment is needed depends upon the type of turf area concerned and the standard of quality desired or required. For golf courses, damage in roughs is more tolerable than damage in fairways, and damage on tees and greens may not be tolerated at all. Many books and extension publications on turf insect management often mention “population thresholds.” Thresholds are the numbers of pest insects present in a given area (usually per square foot, yard, or meter) that warrant control. The concept behind using thresholds is to reinforce the IPM principle that application of a pesticide is not always warranted simply if pests are present. Pests must be present at populations high enough to eventually cause damage. In high cut turf, 5 to 10 cutworms or armyworms per yd2 may just begin to show damage. However, two to three cutworm spots on a high quality golf green may be more than can be tolerated. Thresholds will have to be established for each golf course depending on the standards desired.