By: Island County Extension Agent, Donald B. Meehan
EUROPEAN CRANE FLIES DAMAGE LAWNS AND PASTURES
Each year in August and September we all see what appears to be Texan-size mosquitoes. Most of the time they appear up against screens and windows, attracted by the evening lights. They can often appear in hundreds or thousands. Many people unfamiliar with them fear that they might sting or bite.
These mosquito-appearing insects are called European Crane Flies. They pose no physical threat to humans or pets. In fact, the only problem they create in the winged form is being a nuisance. They do create a problem for many homeowner's lawns and flower gardens and pasture owners in the spring when they are in the larval stage. A common term associated with this worm stage is Leatherjacket.
Even though the European Crane Fly is largely a lawn and pasture pest its larvae has been found eating on a variety of other plants such as flowers, vegetables and small fruits. The larvae will develop in soil from eggs laid during August and September. Most of the time the eggs are laid in grassy areas. The egg laying will generally take place within a 24-hour period after emergence of the winged form. The eggs quickly hatch into small gray-brown worm-like larvae which soon develop a tough skin. It is the tough skin that gives them the name Leatherjackets. The Leatherjackets then feed on the root crowns of grass and clover during the fall. They winter over in the same state of development and resume feeding once spring temperatures increase.
When damp, warm nights come along they will often come out of the soil and feed on the surface. The damage done is not noticed until spring arrives. Many times this damage simply appears as a weak lawn or as brown patches in the lawn or pasture. When mid-May rolls around the Leatherjackets stop feeding.
How do you know if your lawn's brown spots or unhealthy looking areas are caused by Crane Flies? The first thing you need to do is to select 4-5 random spots a foot square in your lawn to dig up. You will only be interested in looking at the root crown zone, so a depth of 1-2 inches is adequate. Then you will need to pull the roots of the sod apart a bit to see if larvae are present. If you try to do this in the fall they will be difficult to detect since they are quite small. If done in the spring you will easily find larvae up to an inch or so in length.
The survey is best done during March. If you count 25 larvae per square foot on the average, then you should probably consider chemical treatment. Researchers have found that counting earlier than March may lead you to apply a pesticide when one wasn't needed. This is because larvae populations can drop suddenly through natural control.
Fall spraying to control Crane Fly is not recommended for homeowners, only commercial turf growers. Any applications of a chemical for Crane Fly control in the fall is seen as a preventative measure. Even though it works, it is a very poor use of chemicals and is not environmentally sound.
If natural controls are not working for you then you will want to use one of two chemicals recommended effective by WSU Researchers. They are Diazinon and/or Dursban. These two chemicals are best applied in the spring between April 1st and April 15th, after a survey count has been made. This application period is not set in concrete, a lot depends on weather conditions. In the past few years March applications would have been effective.
If your Crane Fly problem exists in a pasture your chemical choices are fewer. I have a publication available to of $.25 called EB-0856, The European Crane Fly: A Lawn & Pasture Pest, which covers the use of chemical control measures. You can obtain a copy by calling our office at 679-7327 or 321-5111, Ext.327, or by writing P.O. Box 667, WA 98239.
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