Understanding Cranefly Control on Lawns

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Mary Robson (Ret.), Area Extension Agent
Regional Garden Column April 4, 1999

Written by WSU Specialists Drs. Art Antonelli, Entomologist and Gwen Stahnke, Turf Agronomist

Lawn damage from European cranefly may show up when lawns begin their spring growth spurt. Brown or dead patches in the lawn can result from the feeding on turf roots and crowns by the cranefly larvae. In our work as specialists for Washington State University WSU Extension, we get many questions about timing of controls for European cranefly. WSU adheres to spring (mid March-mid April) control measures, if they are needed. We infrequently recommend fall (mid October-November) control measures in severe cases.

What should be done now?

Monitor for cranefly larvae presence. Craneflies over-winter as larvae in the ground at fairly shallow depths with a weak hibernation which is temperature driven. Washington can have some mild spells during winter which can be described as "shirt-sleeve" weather. If this weather persists several days or more, cranefly larvae "wake-up" and begin to feed. When populations are very high, 30 or more larvae per square foot, serious damage could occur. If these circumstances occur, then this is the rare case where winter treatment would be warranted.

In most years the standard recommendation, given a normal winter, would be to assess the population numbers in mid-late March and treat only if needed. Make only one application if applying an insecticide. Chlorpyrifos (sold as Dursban) is registered (until December 31, 2001) for and recommended for cranefly treatment in western Washington. Read the label carefullly when using any pesticide. Diazinon is not recommended by WSU because of toxicity to birds.

Multiple insecticide applications are not needed. Alternative biocontrols with beneficial nematodes or insect growth regulators have been shown to reduce larval population numbers by up to 40% under ideal conditions. This could bring the population below the damage level, but will not eliminate the cranefly larvae population completely.

A balanced fertilizer program has been shown to improve the turfgrass' ability to outgrow potential damage caused by feeding of cranefly larvae. Proper fertilization, aeration or thatching if needed, to help the lawn outgrow the infestation, eliminates need to make an insecticide application in many cases.

Monitoring European Cranefly Populations

Survey the turf area in early spring (February-March) or when temperatures are consistently warmer. Select three or four random spots in the lawn, 6"x 6" (0.25 sq. ft.). Dig up the top layer (1 to 2 inches) and tear apart samples to count the larvae. Larvae will usually be located at the base of the vegetative layer (thatch) or very shallow in the soil. Multiply the number of cranefly larvae you find in each sample by 4. If this number exceeds 25 per square foot, and the turf is thin, consider a chemical control. If the lawn is generally unthrifty, treatment at lower levels (10 to 15 larvae per square foot) may be necessary. Healthy lawns on which growers use best management practices have been known to have 40 larvae per square foot and not show any damage. If you are uncomfortable monitoring and evaluating the status of the lawn, consult with a professional applicator to help you to make a management decision.

If larval sampling is done by a professional turfgrass manager, use a 4-inch-diameter cup cutter to pull cores in three or four random spots on the lawn. Cores should be 1 to 2 inches deep. Tear them apart to count larval numbers. To determine the average number of larvae in the lawn, add the larval numbers per each core together and divide by the number of core samples taken. Multiply this number (average crane fly number per core) by 11.5 to give you the average number of larvae per square foot in the lawn.

Facts about winter cranefly controls:

The question of controlling European cranefly in the winter, or even in the fall, is one that is asked frequently. We discourage winter (December-February) pesticide applications. There are several reasons for this attitude.

• Cranefly larvae are not always damaging to turfgrass in the fall and winter months. Early researchers found that 50% of over-wintering larval populations can succumb to various diseases, etc., and do not survive until spring when the majority of the damage due to feeding is done.
• Insectivorous birds that remain in our landscapes through the winter have learned that cranefly larvae are an easy, concentrated winter food source. Birds have died dining on them following an insecticide application of diazinon. This is not one of the products currently recommended by Washington State University for control of European cranefly larvae. Care should be taken to read the label on any product and apply the product very cautiously via recommended label procedures. Keep away from open water sources when mixing or applying.
• There can be selected situations where fall or even winter applications might be acceptable and even recommended. Fall applications for control of young larvae on golf greens is expedient, since even small populations can interfere with putting green quality. Since there is only one generation per year there would be absolutely no need to treat the following spring. This is probably the only time we would recommend fall treatments unless lawns were badly damaged during the growing season (usually in areas of very recent invasion). If the homeowner realized too late what was happening and failed to treat in the spring, a fall application, (mid October) may make sense, if populations were exceedingly high going into the fall.

Thanks to Dr Art Antonelli and Dr. Gwen Stahnke for this information.

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