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Sampling Crane Flies 

Here are some simple guidelines for monitoring crane fly populations, all you need is a cutting utensil, ruler and a handlens.

What To Sample:crane fly larva

Larvae, or leatherjackets, are the damaging stage of the crane fly's life cycle. You will be looking for grub-like tubular worms. These larvae come in many different sizes depending on the time of year you sample for them.

When To Sample:

Sampling can begin as early as January, however during some years the larvae are small and difficult to see. In February and March, larvae increase in size and become more apparent.

Where to Sample:damaged area

Select four areas in your lawn, these can be randomly made or you can look for suspicious signs of damage. If you choose to look at damaged areas, sample on the margins of the damage; don't sample bare ground. Another good clue for finding suspicious areas to sample, look for birds especially robins, starlings and gulls. Many times I have found crane flies by looking for holes punched through the grass by bird beaks. Birds are excellent crane fly scouts.

How to Sample:
cutting a sample
Once you've located your site, get your handy ruler out and measure a six inch by six inch square.

Using a knife or cutting implement (I prefer using a butter knife so I don't stab myself by accident), score the area by cutting into the ground about 3 inches deep (just deep enough to cut through the dense root mass).
larva in root zone
Pull back the turf sample. Grass is usually tough and will hold together.
First inspect the hole in the turf for any larvae. Sometimes they are feeding in the zone where the roots pull away from the soil, these larvae will spill out as you pull up the sample.
Then inspect the edges of your sample; many times you will cut into the larva. If you do this enough, you will become an expert on how to determine the difference between sliced earthworms and leatherjackets.
break up the sample
Begin to break up the sample; many times the clod will tear along areas where there are crane flies. Look for larvae in the thatch layer of the turf, this is where most larvae prefer to hang out and feed, about ½ inch deep.

Count all the larvae you've seen. larvas size
Multiple this number by 4 to determine the number of crane flies per square foot of lawn.
Replant your sample back into the divot that was created. Turf is hardy and will reestablish with no problems and it will become unnoticeable shortly.

Repeat this three more times to find the average number of crane flies per square foot of lawn.

Now that you have a good idea how many crane flies you have in your lawn, read on and make an educatued decision about what to do. >>

Decision-Making 


Average number of crane flies per foot2 Your Decision
0 to 25 Do nothing; fertilize appropriately. May need to treat if turf is young, not well established or with poor root structure.
25 to 50 If your lawn is vigorous and healthy, do nothing. Decisions are based on the health of the turf, your personal tolerance, location and use of the turf
50 to 80 Treat crane fly problem. Look towards long-term solutions, such as replacing problem areas with a turf alternative species.

Treatment Options  
What to do? (Management)

Some management options for you. Please also contact your local Master Gardener for advice.

Do-Nothing

A healthy lawn will easily recover, even when the population of leatherjackets is high. Watch weeds if sparse patches appear and reseed if necessary.

Leatherjacket populations can decrease as much as 50% during winter months and between March and May because of predators and natural causes.

Cultural Management of Crane Flies

Grow lawns where lawns do best. Only establish turf in sunny locations. Shade can reduce vigor and promote the survival of crane fly larvae. In areas of low sun, consider a turf alternative groundcover.

Remove excess thatch. Thatch is that layer of old dead grass stems that builds up and reduces the availability of nutrients and water if it gets too thick. Having thatch is good but too much provides a nice environment for crane fly larvae. In fact, just below the thatch is where you can find most crane fly larvae feeding.

Aerification cuts and brings to the surface soil and root cores that then reintroduces oxygen into the soil, which results in stimulating root development. Aerification also improves the movement of water and nutrients into the soil.

Mow your lawn regularly. The correct mowing height is a function of the type of grass species in your lawn. During the summer, mowing every week or so is needed, as you never want to remove more than 1/3 of the total grass blade length. Waiting longer between mowing and removing more of the grass blade weakens the grass. When you mow, leave the grass clippings on the lawn, as they provide a safe source of recycled nutrients and thereby reduce the need to additional fertilizer.

Lawns do need some fertilization, although not as much as is sometimes applied. Mulching your cut grass clippings directly on the turf also reduces this need as well.

Let your lawn go dormant during the dry months. Crane flies are actually semi-aquatic insects and enjoy a moist environment. Dry soil conditions in late summer and early fall may increase crane fly mortality.

If watering is required, it should de done infrequently but sufficiently long enough duration so to wet the entire root zone. This means applying about one to 11/2 inches of water every four to six days and nothing in-between. These infrequent but deep waterings build deep and strong root systems that tolerate crane fly damage.

Keep your lawn well drained. In areas where the soil is saturated by water most of the time, consider planting something other than turf.

Biological Control of Crane Flies

Encourage birds to visit your yard, especially in the winter and spring months. Bird predation can reduce a heavy population of crane flies to just a few larvae in a short time.

Reduce the amount and frequency of all pesticides (herbicides, fungicides and insecticides) in your yard. Predaceous ground beetles feed on crane fly larvae (along with many other pests too).

Chemical Management of Crane Flies

If you've sampled your lawn and know that you're one of the few with an actual crane fly problem, you may decide to arm yourself with a pesticide. Apply suitable chemicals between Information regarding chemical treatment of crane fly can be found on the WSU Hortsense. Follow use, storage, and disposal directions on the label. It's the law.
 
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