Here are some simple guidelines for monitoring crane fly populations,
all you need is a cutting utensil, ruler and a handlens.
What To Sample:
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:
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:
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).
Pull back the turf sample. Grass is usually tough and will hold
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
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.
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
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. >>
number of crane flies per foot2
||Do nothing; fertilize appropriately.
May need to treat if turf is young, not well established
or with poor root structure.
||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
||Treat crane fly problem. Look towards
long-term solutions, such as replacing problem areas
with a turf
to do? (Management)
Some management options for you. Please also contact your local
Master Gardener for advice.
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
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
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
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
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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