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Black cutworm larva feeding on bentgrass from its burrow at night.
Species:
Agrotis ipsilon (Hufnagel) is a primary pest of golf course greens, tees and fairways throughout the United States. This species rarely causes damage to lawns.
[Phylum Arthropoda: Class Insecta: Order Lepidoptera: Family Noctuidae]
Black cutworms can not overwinter in northern areas (light green), but they may overwinter in the transitions zones in mild winters (medium green). They can easily overwinter and remain active all year in the southern zones (dark green).
Distribution:
The black cutworm is a native to North America but has been spread world wide by accidental introductions. The black cutworm is actually a semitropical species that 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 when daytime temperatures rarely exceed 60 to 70 degrees during the daytime.
Hosts:
All species of turfgrasses, except for Kentucky bluegrass, may be attacked. Black cutworms most commonly damage the short cut turf found on golf course greens and tees, whether bentgrass or bermudagrass.
Damage Symptoms:
Cutworms are so named because of their generalized nocturnal feeding habit of cutting off plants close to the ground. On golf course greens and tees, black cutworms rarely cut off turf stems but graze on grass blades of short cut turf. This causes circular or finger-shaped sunken marks. Visible damage in higher cut turf is rare and a general thinning or persistent bird feeding may be the only signs of cutworm presence.
In turf, black cutworm females seem to lay their eggs singly and near the tips of grass blades.
Description of Stages:
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. Mature larvae can be 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.
Black cutworm larvae have a cobblestone surface which is barely visible with a hand lens.
Black cutworm adult.
Life Cycle and Habits:
The black cutworm overwinters as larvae or pupae only in the southern states and migrates to the northern states in early spring as moths. In the northern states, these caterpillars 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 feed at night on 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 1200 to 1600 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) when they reach late instars. They apparently build new burrows every few nights.
Most of cutworms take 20 to 40 days to complete their larval development. 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:
Eriophyid mites usually are not always killed by normal miticides but may be killed by many insecticides. With the use of fine textured bermudagrasses on golf courses, this mite seems less abundant
Sampling
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
Thresholds
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 or yard) 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.
Cultural Control - Use Resistant Grasses -
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. Cutworm larvae develop well on bentgrasses, annual bluegrass and nonendophyte ryes and fescues.
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 - Insect Parasitic 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 - Bacillus thuringiensis (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 organophosphate, carbamate, pyrethroid and diacylhydrazine insecticides effectively control cutworms in turf. On golf course greens and tees, it is recommended that spraying a band of turf surrounding the affected area (a minimum of one boom or spreader width) will help keep larvae from moving back onto the greens from surrounding turf.
Preventive Treatments.
Field tests with chloronicotinyl insecticides (usually 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. Field tests with azadirachtin (=neem, a botanical insect growth regulator insecticide) have given effective control of black cutworms on golf course greens and tees when applied at regular 14 to 21 day intervals, starting in mid-May. Similar results have been obtained using spinosad-based insecticides (i.e., at regular intervals of 21 to 28 days).
