Insect Management In Turf & Ornamentals

Proper siting is critical, as certain plants become stressed when not located according to their needs for sun/shade, drainage, wind protection, pH range and nutrient availability. A popular phrase embodies this first consideration – “right plant, right place.” For example, there is nothing more spectacular than an azalea or redbud in full bloom. However, if not placed in an understory environment that provides several hours of shade each day with protection from bitter winter winds and good drainage, these plants will suffer and decline over time. In too many situations, novice homeowners or inexperienced property managers place plants such as these in newer developments, without tree cover or other critical needs of the tree or shrub being met. The common result is a sick plant, riddled by borers or covered with aphids.

Get plants off to a good start by using appropriate installation techniques. The old saying, “a 50-cent plant in a $50 hole” is still a good one. Soil preparation is very important, as is the digging of the hole. When establishing turf, spend the extra time to prepare the seedbed with a power rake, slicer or similar machine. Young turf roots must have loose soil in which to grow or the plants will be weak and pest susceptible. The same holds true for tree and shrub roots. Endeavor to dig a wide hole, one in which the roots will be able to grow laterally with ease.

Use restraint when amending the backfill soil. In most situations, it is best not to mix the soil with compost, peat moss or rice hulls when planting woody plants. In fact, the woodier the plant, the less amended soils should be used. This is a practical matter relating to the ability of the roots to expand beyond the planting hole over time. Since trees and shrubs often develop root systems which will grow 20 to 70 feet laterally, it is not feasible to amend these soils. Furthermore, young roots will preferentially tend to remain in a heavily amended planting hole, actually restricting desirable lateral growth. By contrast, the roots of most annuals and perennials are not likely to exceed the planting hole width by more than a few feet, so it is desirable to amend the soil to the expected diameter of the mature root system.

Landscape maintenance is often overlooked or neglected, possibly because it is commonly thought to be a less interesting procedure. Proper attention to adequate watering, pruning and mowing will keep the plants healthy and thrifty, naturally able to resist most pests. For example, a properly mowed, fertilized, and watered turf will develop a deep, fibrous root system. If white grubs become established in a particular neighborhood, those lawns with extensive roots will suffer much less damage than lawns with shallow, weakened root systems.

PEST KNOWLEDGE. Insects in the landscape are commonly divided into five categories based on their feeding habits:

• insects that feed on leaves
• insects that bore into wood
• insects that feed on plant juices
• insects that produce galls
• beneficial insects

Leaf-feeding insects include beetles, caterpillars, sawflies and leafminers. These pests remove essential plant tissues and structures through their chewing, skeletonizing or leaf-mining behavior. Insects that bore into wood invade and destroy the conductive vessels of the plant, interrupting water and nutrient flow. Continued feeding by certain borer species can destroy the inner wood causing branches and stems to break off in windstorms.

Insects that feed on plant juices generally insert straw-like mouthparts into the leaves and extract cell sap containing water and nutrients. Other sap feeders, such as thrips, rasp and tear plant surfaces, then feed on the exposed juices. If enough leaves are damaged, the plant will suffer or die.

Gall-producing insects generally are not considered important plant pests. Insect- induced plant galls are usually rounded bump- or gall-like structures that distort the shape and appearance of plant leaves and stems. The injury resulting from galls is mostly from the displacement of leaf or stem tissue used in building the plant gall. The unusual look of a heavily gall-infested plant, however, may detract from the aesthetic value of the plant.

Beneficial insects feed on other insects and mites, usually those that landscape managers consider to be pests. Lady beetles and lacewings are good examples. Both feed on aphids, beetle larvae, small caterpillars and many other small insects. Beneficial natural enemies such as these should be welcome in your landscape as they can remove large numbers of injurious insect and mite pests.

ACCURATE PEST IDENTIFICATION. An important step in a successful insect management program is accurate pest identification. Many novice grounds managers tend to skip this step, anxious to get on with some sort of spray program. In many cases, that unidentified insect turns out to be a noninjurious species or, in some cases, a beneficial natural enemy busily consuming insect and mite pests. Accidental spraying of these beneficial insects can lead to secondary pest problems when natural enemies are eliminated from the landscape.

Proper tools will help landscape managers in their quest for accurate insect identification. Every person on the staff should be equipped with a 10x hand magnifier. This will allow them to see distinguishing body features such as color patterns, markings, number of wings, etc. Also, a small probe and collection vials will facilitate returning insect samples to the shop where they can be more closely examined. Identification books are also helpful, especially ones with good color pictures. (A standard volume for the landscape industry is “Insects That Feed On Trees and Shrubs” (ISBN 0-8014-2108-X) by Johnson and Lyon. It is readily available through most bookstores.)

EARLY PEST DETECTION. Regular inspection of the trees, shrubs and turf in your landscape is just as important as driving to work every day. If either is skipped, unacceptable outcomes are likely. Early detection of insect pests is very important because most pest infestations start out at low levels and build as the season progresses. As you travel around your clients’ properties performing mowing, fertilizing or other services, pause for a moment to inspect each tree, shrub and turf area on the property. Observe how turf and landscape plants in each area or “zone” of the grounds appear. If you discover an insect or mite infestation, consider how much damage is already present and how much it is likely to cause in the future.

Remember that a minor pest infestation may never reach levels requiring treatment. For example, it is difficult, and often unnecessary to control a caterpillar infestation on a large shade tree in good health, as they can tolerate a considerable defoliation without serious long-term harm. Also, while monitoring your landscape, don’t forget to check for beneficial insects to gain a sense of their abundance and activity against potential insect and mite pests.

DAMAGE THRESHOLDS. Certain plants can withstand considerable insect feeding, while others are much less tolerant. A few insect pests feeding on most healthy trees or shrubs pose little or no immediate threat to the plant’s health and vigor. For example, fall webworm caterpillars feed in large numbers on crabapple leaves in the autumn months. However, in most cases, healthy crabapples can tolerate almost complete defoliation and remain unaffected the following spring as long as the tree’s appearance is acceptable to the client. This is because a large share of the nutrient, carbohydrate and sugar production has already taken place for the year by the time the insect feeding takes place. On the other hand, a moderate to heavy infestation of pine sawflies on a small scotch pine is quite serious, as major injury can result. In just a few seasons, a heavily infested tree can lose vigor, become weakened and perhaps even die. In this case, the pest damage threshold is very low.

Damage thresholds are different for every plant and every insect pest. Kentucky bluegrass, for example, is noted for its shallow root system in late summer, while tall fescue usually maintains deep and extensive roots. Eight to 10 white grubs per square foot can cause considerable damage to bluegrass, while the same number of grubs in tall fescue would cause much less injury due to the greater mass and expanse of tall fescue roots.

EFFECTIVE INSECT CONTROL. As previously stated, an effective insect management program uses a combination of strategies to effectively control pest populations. Physical control of insects is possible in some cases, especially on low growing trees and shrubs. Handpicking and forceful blasts of water work quite well to control small numbers of bagworms, tent caterpillars, fall web-worms or pine sawflies on ornamental plants. Physical methods of control are especially useful in sensitive “pesticide restricted” areas, such as zoos or children’s playgrounds.

Biopesticides have gained in popularity and effectiveness over the past decade. These pesticides are derived from living organisms (plants, bacteria, fungi) and generally have fewer adverse environmental side-effects. Products such as Dipel and M-One are formulations of the bacterium Bacillus thuringiensis that causes insects pests, such as caterpillars and beetles, to cease feeding and die from gastrointestinal disruption. These bacteria occur naturally in the soil and haven’t been found to have any adverse impact on the environment.

Horticultural oils and insecticidal soaps also fall into the category of environmentally friendly insecticides. They can be quite effective for controlling certain leaf- feeding insects and mites. Traditional organophosphate, carbamate and pyrethroid insecticides run the gamut of varying levels of toxicity, depending on active ingredient, formulation and residual activity in the environment.

All foliar-applied pesticides have limitations. Thorough coverage of the leaf surface is essential to achieve satisfactory control. When spraying large trees, the issue of pesticide drift is an important consideration. The more toxic the pesticide, the more hazardous the drift. Pesticide injection of trees limits drift, as the insecticide is placed directly into the tree trunk, and is thus less likely to be carried to nontarget areas. Repeated treatments, however, can injure the tree, as wounds are created in the tree trunk each time the insecticide is applied. Continued reliance on injection for insect control can be detrimental to trees in the long term.

Establishing an IPM program for your landscape will require time, effort and careful planning. The potential rewards, however, are substantial in terms of improved pest control and reduced reliance on pesticides for insect and mite control.