CORVALLIS - There may be leatherjackets munching your lawn.
No, there's not a motorcycle gang having a picnic in your yard. There's a non-native species of crane fly - the European crane fly ("Tipula paludosa") - now found west of the Cascades, whose large leathery larvae feed on plant roots, including the grass in your lawn.
Many people know crane flies as "mosquito hawks" or "Montana mosquitoes." As adults, crane flies are those giant mosquito-like insects that hover about your outdoor lights in the summer and fall.
These leggy flies may look big and scary, but really do no harm as adults, explained Jack DeAngelis, entomologist with the Oregon State University Extension Service. It is the larvae, called 'leatherjackets' by some, that sometimes overwhelm a lawn, pasture or golf course, causing it to die back in patches.
European crane flies lay their eggs in grass in the summer or early fall. The eggs hatch into larvae or maggots, known as 'leatherjackets' because of their gray-brown leathery skin. European crane fly larvae live in the soil and feed voraciously on the roots, shoots and crowns of grass plants during the fall and following spring. Eventually the leatherjackets grow to a whopping inch to an inch-and-a-half long.
Normally, this is not a problem unless, of course, leatherjackets happen to be in dense populations in your lawn, pasture or grass seed field.
"Usually very little damage is done to plants by these creatures, including lawn grasses, because plants have a remarkable ability to compensate for minor root damage," said DeAngelis.
But when the population levels build way up (to more than 25 to 30 larvae per square foot), lawns begin to thin and die back. This dieback is especially noticeable in the spring. Damage can also occur when birds come in and scratch at the lawn surface looking for larvae to eat.
If you suspect leatherjackets have invaded in your lawn, DeAngelis suggests the following:
- Scout your lawn for European crane fly larvae. Spring is the best time, as damaged areas show up the best. Dig a patch of lawn out, about 12 inches square and about two inches deep. Then count the number of leatherjacket larvae you see in this patch. If there are more than 25 of the leatherjacket larvae, you might consider treatment or lawn renovation if your lawn has severe damage. If there are less than 25 per square foot, then your lawn grass can probably outgrow the munching maggots. If you renovate your lawn, it is probably not necessary to treat it with insecticide prior to renovation, said DeAngelis.
- Consult a current edition of OSU's "PNW Insect Control Handbook," on file at local county offices of the OSU Extension Service, for specific control suggestions. The recommended choices for home gardeners include the use of beneficial nematodes or insecticides, available at lawn and garden stores. Fall (October) or spring treatment is recommended as best. Keep in mind that birds are important predators of crane fly larvae. Take great care not to poison birds if you choose to use insecticides.