They may be leatherjackets, but they don't drive Harley's

They may be leatherjackets, but they don't drive Harleys

Craig MacConnell
Washington State University
Cooperative Extension
Whatcom County

One of the most ungainly members of the insect world, the European Crane Fly, stumbles and bumbles into our lives here in Whatcom County each August. We experience the adults for about eight to ten weeks each year, but the crane fly is here in other forms year round. Most of the time this insect resides as a larvae, called "leatherjacket" in the soil, most frequently in lawns. And oh, by the way, the adult doesn't bite, sting, or even eat!

Recent low level detection's of common insecticides, Dursban, diazinon and malathion in stormwater collection basins and streams in the Lake Whatcom watershed lead me to suspect that homeowner attempts to control crane fly is the most probable source of this material.

In certain circumstances and populations, crane fly can be damaging to lawns and even other landscape plants, but not often. Most of the time, healthy lawns can tolerate well the presence of these insect pests, particularly considering the naturally occurring population controls underway in the landscape.

Reducing the amount and methods of use of pesticides to control this insect will contribute to the protection of our water resources, including Lake Whatcom, and still provide for healthy lawns or other ground cover substitutes in our yards.

Smart Management

These days Whatcom County farmers, along with their counterparts around the world, are implementing what one Whatcom County raspberry grower has called "smart farming" or integrated pest management (IPM). IPM is a process where the land manager actively makes decisions about pests. This systematic decision making include such questions as:

How do I maintain a healthy landscape so that my plants more readily tolerate pest damage.

Is this pest of such importance that I need to intervene and do something, or will nature, including a healthy plant, tolerate the damage with no significant implications?

If I do decide that intervention is required, what is the best choice among alternative methods. Best choice here includes consideration of the impacts on the environment. Alternative methods only include those that are expected to be effective.

Home owners can adopt the same decision making process to determine whether a pest is significant or not and if it is, choose the least environmentally disruptive approach as the appropriate method of response.

The first approach for European Crane Fly should be to select the most appropriate ground cover for the landscape. For high use areas to accommodate children playing and dogs running, lawns may be the most resilient choice of plant material. For aesthetic value to look at in the landscape, many people prefer lawns, but there are many other groundcover plant choices that are not subject to crane fly like lawns are.

Grow healthy lawns

If you do have and want to keep your lawn, then it is important to keep it as healthy and vigorous as possible so that it can tolerate most levels of crane fly larvae feeding. Here are some of the key ways to keep your lawn in high vigor.

Grow lawns only in sunny locations. Significant shade weakens the turf.

Remove the build up of thatch. Thatch is old grass stems that build up on the surface of the soil, under that green blades you see. Thatch restricts the movement of water and nutrients into the soil and the roots of the grass. Removal of thatch is done mechanically with equipment that is usually rented or hired out.
Another way to boost the strength of the root system besides removing thatch is the process of aerification. Aerification is also usually done mechanically with rented equipment. This process 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. Bentgrass predominates in most older lawns here in Whatcom County. Newer lawns often are comprised of mostly perennial ryegrass and creeping red fescue. Bentgrass produces much more thatch than ryegrass and fescue, although all will benefit from dethatching. Bentgrass should be mowed much lower, to about ¾ of an inch, while the newer lawns containing rye and fescue should be mowed to 1 to 11/4 inches in height. During the summer this means mowing every week or so, 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. If the grass is wet when you mow, you may need to knock the clumps apart so not to smother the living grass below. I find that the back of a lawn rake works well.

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. Research indicates that grass benefits from more nitrogen and potassium than phosphorus, which is good, because phosphorus is a direct and major threat to surface water, such as Lake Whatcom. So look for fertilizer that has the three numbers in this ratio 3-1-2 or 6-1-4 or close to it. The first number is nitrogen, the second, and the one to minimize in the Lake Whatcom watershed is phosphorus, and the last number is potassium.

If you want a green lawn in the late summer, then irrigation is important. Having said that, your lawn will not die, but rather go dormant, with a brown color, in the summer without irrigation with no harm to its overall health. The root system of a healthy lawn is at least a foot deep in the soil. Watering 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 a deep and strong root system. You can easily tell how much water you are applying by placing an empty tin can or two out on your lawn to measure the collected spray. Make note of how much time it takes to collect an inch of water in the can.

So, all of these management actions highlighted above help make a strong and healthy lawn that can easily tolerate the attack of crane fly on most lawns. This approach should be the first line of defense and will greatly reduce the need to take any other action, including the use of insecticides, on your lawn.

If you suspect that your lawn is under an unusual level of attack by crane fly, then its time to employ some more IPM tactics.

The cycle of life

The first issue is understanding the life cycle of this pest. The adult crane fly emerges from the soil from late August to mid-September. They immediately mate and lay eggs. This is not the time to take any action. The eggs in the soil quickly hatch and gray-brown, worm-like larvae, with a tough skin, called a leatherjacket starts to develop and feed on roots. The feeding slows dramatically in the winter and recommences in early spring. Feeding ends in mid-May. The larvae change to a quiet pupa in July and August to appear as adults in August and September.

Enter the other European

It is important to understand that there are many natural forces that reduce the population of crane fly larvae in the soil, without any intervention. There can be significant death of leatherjackets in the winter due to cold and disease. There is also significant predation by birds feeding on the larvae. The European Starling, that aggressive bird that drives away native songbirds from our yards, has a redeeming value in being a very effective leatherjacket predator. They also can serve as an early warning sign that there is (or was) crane fly larvae in your lawn. So, let them feed to their heart's content.

Monitoring and decision making

You can investigate and find out yourself the level of crane fly larvae in your lawns. Research has given us thresholds or levels of infestation that helps us decide to relax or take further action. Here is what to do;

In February or March select three or four random locations on your lawn. This time of year is selected so to let the normal winter death of larvae to take place.

With a shovel or spade cut three sides of a six inch by six inch square about 1-2 inches deep and peel back the sod to expose the bottom of the lawn grass.

Count the number of leatherjackets you find. They will be right there in front of you.

Multiply the number of larvae found in each location by four. This gives you the number per square foot, the reference for recommendations.

If your count exceeds an average of 25 larvae per square foot in a healthy lawn, then some management action may be appropriate. The action threshold for weak lawns is lower - about fifteen larvae per square foot.

I want to reiterate that the most important action is making and keeping your lawn healthy and vigorous. See the recommendations above. If you have taken all of those actions, and you find high levels of crane fly leatherjackets in the spring, then you might wish to consider a further step of an insecticide. Or you may decide to convert your lawn over to other forms of ground-cover will be more successful in your yard.

There are a number of insecticides that are registered by the EPA for use by homeowners on crane fly. The two most commonly used are chlorpyrifos (Dursban) and diazinon. Both are available in granular and liquid form, although some liquid formulations are not available to homeowners, because special licensing is required to purchase, handle and apply them. Due to its toxicity to birds, WSU does not recommend diazinon for crane fly control. . Chlorpyrifos is the preferred material and is very effective against this pest. Granular formulations are usually safer to the user because there is a smaller percentage of the "active ingredient" in the formulated product and therefore the likelihood of exposure and possible harm to the applicator is reduced. It is important to avoid the tendency to over-apply the granules to the point where they are easily visible on the lawn surface. Apply according to the label directions. Liquid formulations are equally effective and may be preferable because there is less tendency to over-apply. Regardless of the formulation used, care must be taken to use them properly so that they reach the target pest (crane fly larvae in the soil) and do not effect non-target species near the home or in nearby waterways. Unfortunately, both chlorpyrifos and diazinon have recently been detected in surface waters in the Puget Sound Basin, including Lake Whatcom. If you live in the Lake Whatcom watershed, please consider the special responsibilities of affecting the water supply for close to 100,000 people with your actions.

Other choices on the horizon

There exists a number of different kinds of microscopic insect killing nematodes (roundworms) that have the potential for seeking out and killing crane fly larvae in lawns. Unfortunately, in the past, research has indicated that these are not effective in the cool soils we have in the Pacific Northwest. Recently new types have been identified that are supposed to be more effective at cooler temperatures. We intend to conduct some research on the effectiveness of these new types right here in Whatcom County soon. If they appear to be effective they will become a highly desirable option for those lawns that monitoring indicates a serious threat from crane fly larvae.

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Questions, comments and contributions directed to Todd Murray or Sharon Collman