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Ecological Approach to Lawn Care (Including Crane Fly Control)


January 2002

Pest Control

Ecological Approach to Lawn Care (Including Crane Fly Control)

by David Johnson

David Johnson is former director of grounds maintenance at Children’s Hospital and Medical Center in Seattle. For fifteen years he used integrated pest management techniques to manage their extensive plant collection.

The lawn surrounding your home can be a source of delight or cause for despair. Our society has traditionally valued the aesthetic standard of a uniform, dense, close-cropped and geometrically edged lawn. Trying to maintain such artificial standards, perhaps more to please the neighbors than ourselves, we can set ourselves up for failure. We also allow ourselves to become easy victims of advertisements promoting a lethal assortment of chemicals guaranteed to solve our lawn care problems.

Some lawn service companies that rely heavily on quarterly or bimonthly pesticide applications leave the consumer with the perception that healthy attractive lawns require frequent applications of assorted chemicals. It is not part of the sales plan to offer information that will reduce pesticide use.

Generally speaking, the lower your tolerance for any deviation from the “perfect” putting-green style lawn, the more likely it is that chemicals will be needed to achieve it. Actually, it turns out that the much touted, deep green lawn is not the healthiest turf. A lighter green lawn has better fertility, root development, and disease resistance.

Many other landscape options are available, from neatly tended vegetable gardens to meadows of wild flowers. Yard design should be dictated by the intended use patterns. Most home landscapes do have at least some areas of grass because it can be attractive and serves a purpose.

Lawn Requirements and Planning

An ecological approach to lawn maintenance begins with appropriate design and installation to provide the physical conditions a lawn requires to thrive. The area the lawn is to occupy must receive adequate light, and the soil must absorb water but drain well. Shady areas and steep hillsides are not good bets for grass. The pH (acidity/alkalinity) of the soil should fall within a range of 6.0 to 7.0 (slightly acidic).

West of the Cascades soil is usually too acid, while east of the mountains excess alkalinity is often a problem. The soil must be deep enough for healthy roots to grow. Six inches is a minimum, and twelve is better. The soil must contain adequate nutrients. Finally, a source of water is needed to maintain adequate moisture levels.

The selection of proper grass seed or sod is just as important. In Western Washington, a mixture of perennial rye grass and fescues are recommended. If sod is used, purchase it fresh.

Mowing

Mowing should always be done with a sharp blade set at the correct height. Never remove more than one third of the grass blade at one mowing because this will diminish nutrient reserves, causing stress conditions and a decline in lawn health. Mowing height for perennial ryegrass west of the Cascades should generally be between 1½ inches and 2 inches.

The taller the grass the deeper the roots penetrate, tapping into a larger volume of moisture and nutrients. Frequent (i.e. weekly) mowing increases grass shoot density, inhibiting the establishment of weeds. Grass-cycling—leaving the clippings on the lawn rather than bagging them—can reduce fertilizer needs by one-third. Specially designed mulching mowers work best, but any mower can be used for grass-cycling if mowing is done often and the blades are kept sharp.

Cultivation

Aeration is the process of removing small cylindrical cores of soil from the lawn, relieving soil compaction and allowing water and air to penetrate. A home lawn may require aeration only once every two to four years depending upon use and soil type.

Thatching removes the mat of old grass rhizomes that develops at the soil surface, preventing the penetration of water and fertilizer. Thatching needs to be done when the thatch layer exceeds about 1/2 inch. (The rate of thatch accumulation differs with grass type.) The job is best done with a special thatching rake or, for large areas, a thatching machine, which is available at rental yards.

Fertilization

Fertilization is a necessary part of a lawn maintenance program. Selection of the fertilizer to use is important. Avoid the so called “weed and feed” fertilizers. Application of these products amounts to indiscriminate broadcasting of chemical herbicides over non-targeted species in the yard, whether or not a pest problem exists.

Fertilizers derived from animal or plant sources are termed “organic.” The advantage of organic fertilizers is that the nutrients break down slowly, a benefit to the diverse flora and fauna of the soil. Plant roots cannot differentiate between nutrients derived from “organic” or “manufactured” sources; they absorb nutrients in only one chemical form.

What is most important is to choose a fertilizer that has the proper balance of nutrients for your geographic area and that contains at least 70 percent slow-release elements. Manufactured fertilizers that contain a high percentage of slow release elements do cost more than quick release fertilizers. They are worth the extra cost because they maintain slow, steady growth that is best for the health of your lawn and they help protect against fertilizer runoff that can pollute nearby water.

Whatever the source of fertilizer, it is important that it be applied at the proper time and in appropriate quantities. Fertilizer does not “feed” plants; plant food is manufactured by the plant using the sun’s energy. Fertilizer supplies the nutrients to the soil solution to be absorbed by the plants’ roots. Nutrient deficiencies lead to a decline in plant health. Excess nutrients in the soil solution, besides representing a waste of resources, can damage plants or cause excessive growth. Application rates vary with the product.

For Western Washington, WSU Cooperative Extension recommends a balanced fertilizer with nutrients in a 3-1-2 ratio. Total nitrogen should be up to 4 pounds per 1000 square feet per year. If you make four applications per year, you would only apply one pound of nitrogen each time.

Timing is very important. West of the Cascades, the most important application is made around mid-November. If you only fertilize once, do it in November; if you fertilize twice, do it in September and again in November. If you choose to make four applications, the other two should be in April and June. Such timing encourages the development of strong root systems which can support vigorous top growth through the spring and summer.

For recommended nutrient levels and application times, consult your local Cooperative Extension office.

Watering

Infrequent, long irrigation cycles allow moisture to penetrate, encouraging deep roots which are capable of withstanding the stresses of drought. Frequent, short cycles encourage shallow rooting which is easily stressed. If the lawn is growing in a fine textured soil which does not readily accept water, the application of a wetting agent may help.

Often during drought conditions the lawn dries up, but the deeper rooted weeds thrive and spread. By maintaining even soil moisture to a depth of 10 inches throughout the growing season, the lawn’s health is assured and weed growth can be inhibited.

Pest Management

Integrated Pest Management (IPM) is an approach that focuses on prevention by considering the ecosystem as a whole. In the case of lawn care, it begins by selecting the appropriate plant types for the area and applying the correct horticultural practices to maintain health.

IPM accepts the presence of “pests” as a natural part of the plant/animal ecosystem and does not seek to eliminate them. A threshold of acceptable pest presence or damage is set, and the area is monitored to determine if pest damage will exceed it. Treatment strategies are implemented only when monitoring shows that unacceptable damage will occur.

Treatment is aimed at preventing pest levels from exceeding the threshold with minimal disruption of non-targeted members of the plant or animal community. The effectiveness of the treatment is evaluated, and the treatment is modified if necessary.

An important part of IPM is defining what level of weeds or insect damage we are willing to accept. This standard will set the threshold at which treatment is called for. Purely aesthetic standards tend to call for treatment at much lower pest levels than do standards based upon plant health. Setting our pest tolerance too low results in unnecessary treatments and possible environmental damage.

Monitoring a pest problem requires identifying the pest and learning about its life cycle. Once this knowledge is obtained, a projection of the pest’s potential as a problem can be determined. Often natural predators can keep pest populations manageable over the long term, despite brief fluctuations at certain times of the year.

When considering a treatment, the goal is usually not to eradicate the pest, but to use the least toxic treatment that will drop the pest level below the threshold. For example, increasing nutrient levels through fertilization might be an appropriate treatment to allow the lawn to successfully compete against a weed or insect. Hand weeding can be an appropriate response in some situations. For more information on weed control in lawns and gardens, see our fact sheet on weed management.

The most important part of any treatment is evaluation. The evaluation may indicate that the treatment be repeated or changed. Often it is necessary to combine a series of treatments to achieve a reduction of pest levels.

Applying the IPM method to home lawn care is not difficult. With a little determination to learn about pest life cycles and horticultural practices, informed decisions can be made which will minimize chemical use without compromising the aesthetic quality of our landscapes.

An Example: Crane Flies

In Western Washington there is only one lawn insect problem that may require treatment. We frequently hear that the dreaded European Crane Fly can devour an entire lawn in a week. Many lawn services and garden centers recommend the application of chemical insecticides as a preventative measure. Under IPM principles we consider this the last resort. Our first line of defense is education.

The Crane Fly spends most of its life cycle as a grub in the soil feeding on grass. It briefly emerges as a large winged insect in the fall to mate and die. The eggs are laid in the soil and hatch out to begin the feeding cycle again. Further reading reveals that many of the grubs die over the winter when the ground freezes. They are a food source for starlings or other birds you thought were pests.

When spring arrives they become more active, and this is when monitoring should begin. Mark out several one foot square patches of turf in various parts of the lawn, and dig down along three sides of each with a spade, then flip the sod over to expose the roots. Count the Crane Fly grubs within each square foot area and calculate the average. If there are less than 25 grubs per square foot, no treatment is necessary.

If levels are between 25 and 40 grubs per square foot, increase the nutrient levels and continue to monitor every two weeks. If the levels exceed 40 grubs per square foot, damage may be significant and a treatment is appropriate. One non-chemical method that may reduce the grub population is to thatch the lawn on a cool, moist day when grubs are at the surface.

Beneficial nematode worms are available under trade names such as Orcon and others. If applied as soon as soil temperatures reach 55 degrees and kept well watered, nematodes can reduce Crane Fly populations significantly. Following treatment of any type, the area is monitored to determine effectiveness.

This is an abridged version of a more extensive fact sheet available in print form from Washington Toxics Coalition for $1.50 plus .50 postage and .13 tax (2.13 total). For more information, visit their web site (http://www.watoxics.org.) Print versions can be ordered from Washington Toxics Coalition either over the Internet or by calling 800-844-SAFE.


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