Trouble from below

To control devastating mole crickets, you should monitor activity, understand life cycles and time controls so that you hit them when they are most vulnerable.

Mole crickets are one of the most destructive insect pests of Southern turf. Their range extends from North Carolina to Florida and along the Gulf Coast to Texas. Their primary hosts are bahiagrass, hybrid bermudagrass, common bermudagrass and centipedegrass. The two species most commonly found in Mississippi are the tawny mole cricket (Scapteriscus vicinus) and the Southern mole cricket (S. acletus). These two species range throughout the Coastal Plain in the Southeast, from North Carolina to eastern Texas. Another species, the short-winged mole cricket (S. abbreviatus), is more localized in the Florida area. The only U.S. native mole cricket, the northern mole cricket (Neocurtilla hexadactyla), ranges from southern New England to Florida and west to the Central Plains. Mole crickets are in the order Orthroptera along with true crickets and grasshoppers.

What are they and when do they appear? Adult mole crickets are 1 to 1.25 inches long, cylindrical and grayish-brown. They have velvety bodies with spade-like front legs adapted for digging. Their eyes are beady and they have a rigid shell for a body that is covered with a dense coat of fine hairs. Their front wings do not quite reach the tip of their abdomen and are folded on their backs. Immature mole crickets (nymphs) are smaller, and their wings are not fully developed. The adult short-winged mole cricket has wings that cover about one-third of its abdomen and is shorter than other mole crickets. Northern mole crickets may be either long- or short-winged.

During the winter months, mole crickets burrow deep into the soil. In the spring, when the soil temperature warms to 60F, you will see mole- cricket damage when they return to the soil surface and begin to feed on grass. Adult crickets mature and disperse by flight during this time. In most southern states like Florida, dispersal flights occur as early as February and usually taper off by May. Flight periods may be delayed for a month as you go north towards the Carolinas.

After dispersal flights, females select egg-laying sites in soil with adequate moisture. They construct a small egg chamber below the soil surface and lay a clutch of about 40 eggs. They then seal the entrance and leave the young to fend for themselves. Eggs usually hatch in 20 to 30 days, and each female may lay several clutches of eggs. Most eggs are laid from April to June.

The majority of eggs hatch in May and June. However, depending on your location, some hatching may occur as early as April and as late as July. After hatching, the young may pass through eight to ten nymphal instars. By the month of December, most mole crickets have developed into adults, but there will be some late bloomers. The imported species generally have one generation per year, but in southern Florida, a partial or full second generation may develop. A partial second generation may also occur in southern coastal areas. The northern mole cricket, on the other hand, may have one generation per year in Florida and take up to two years to complete a generation in the Carolinas.

Mole cricket damage occurs from feeding and from tunneling activity in the upper soil. They can feed both on underground roots and aboveground plant parts. As they feed on grass roots, their powerful forelegs cause extensive plant injury. As the insect burrows in the upper soil, it rips and tears plants, destroys roots and pushes mounds of soil above the surface (see photo below). Feeding occurs primarily at night in the upper inch of the soil, but a single mole cricket may tunnel through several feet of turf in a day. Turf infested with mole crickets may also have a higher incidence of root rots, especially in seedbeds. You must understand the biology of mole crickets to design and implement management strategies for infested sites.

Control timing and management To manage mole cricket populations, you must continually monitor cricket activity to determine their developmental stages and the extent of infestation. Attacking newly hatched, young nymphs before they cause damage is the first step. You should target subsequent treatments at areas where damage is visible. By late fall, the year's damage has occurred and most efforts should focus on reducing the number of adults that will emerge in the spring.

- Spring treatments for adult crickets. In the spring, primarily large adult mole crickets are present. Most dispersal flights also occur during this period. On warm days and nights, considerable damage may occur as the mole crickets actively feed and burrow. If weather conditions turn cold or dry, adult crickets may retreat farther into the soil below the treatment zone. Keep in mind, mole crickets do fly in the spring, so if chemical treatments are necessary, make sure crickets have not flown elsewhere or moved down into the soil to escape cold or dry weather.

Check the presence of mole crickets immediately before treatment by pouring a gallon of soapy water (2 tablespoons of lemon-scented liquid detergent per gallon) on a damaged area (1 to 2 square feet). Wait 15 minutes for crickets to emerge. If you do not detect any, test another area. This procedure usually doesn't kill the crickets, but will force them to the surface for air.

- Early summer treatments are best. Apply treatments in late spring and early summer to target newly hatched, young nymphs before they can cause damage. At this time, they are easier to kill; however they may be more difficult to detect. The young nymphs are small, and surface damage is not prevalent. You may not see the need for treatments. Grass has often recovered from spring damage caused by adults and there may be little evidence of damage from the newly hatched nymphs. However, if adults were present in the spring, despite treatment efforts, mole crickets more than likely will be present in June and possibly throughout the rest of the season.

- Monitor activity and make residual treatments. Mole cricket control is not a one-time, one-insecticide solution. Monitor continually and apply well-timed controls throughout the season. Assess spring tunneling activity so that you can target the treatments. Make maps of turf areas using landscape plantings or distance markers as reference points. Target these sites for treatments during June or July before the newly hatched nymphs cause damage. As the season progresses into the summer, spot treat the most extensively damaged areas.

- Attack early. If you wait until fall (September and later) to treat, mole crickets will be more difficult to control. The crickets are larger, grass growth has slowed and it is getting too late to mitigate symptoms with fertilizer. What you have done earlier in the season will dictate how much damage you will experience in the fall. Don't expect immediate results from late-fall treatments. However, you may reduce the number of reproductive adults, which can pay off the following year.

- Maintain a healthy turf. Most of the time, properly maintained grasses, especially bermudagrass, will outgrow damage caused by mole crickets. This is especially true for spring damage, which is often unnoticeable in the early summer as cricket activity declines and healthy grass revegetates damaged areas. Fertilize on a regular schedule. Healthy, vigorous turf will withstand more damage.

Mole cricket control options There are more chemicals on the market today for mole cricket control than there were twenty years ago when I first started working with this pest. The Insecticide Update on page 52 lists active ingredients that control mole crickets as well as the brands and manufacturers. Be sure to read all label information before using any insecticide.

Turf managers primarily rely on chemical pesticides. Florida has been testing imported natural enemies (parasitic wasps, tachinid flies and parasitic nematodes) for control. However, these methods are still in their infancy. We have tested and used nematodes that continue to infect mole crickets for several years. These nematodes do not destroy beneficial insects, nor do they feed on grasses. If mole-cricket infection does not occur, the nematodes will die. It is important for environmental conditions to be right for nematodes to work. They should be handled carefully and applied late in the afternoon to warm, moist soil that is infested with adult mole crickets. Irrigate after treatment. Nematodes don't work like insecticides. Most often, mole-cricket populations are only suppressed.

To control mole crickets (or any insect), you must know the developmental stages. Once these are known, you will be able to predict insect behavior and time controls to coincide with the insects' most vulnerable stage. If improperly timed, any control technique will fail. However, if you follow these guidelines, your mole-cricket management program will be focused and on time.

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