Managing Diseases and Insects

Properly maintained and healthy turfgrass will tolerate the presence of low levels of pest populations without suffering permanent damage. Healthy turfgrass usually recovers more quickly from insect and disease infestations. However, there may be times, even in healthy lawns, where some pest control is needed to prevent significant damage.

The visual symptoms or signs of lawn problems are often similar and can be easily confused. Poor cultural practices, environmental factors and pest activity can produce symptoms that appear the same. The first step to solving any problem is proper identification. Correct and timely identification can not only save your lawn but your time, money and unnecessary use of pesticides.

Each disease or insect has symptoms that can be associated with it; each also needs a specific set of circumstances for those symptoms to occur. These circumstances involve a host, (in this case a turfgrass plant) the insect or disease itself, and favorable environmental conditions for the insect or disease to develop.

The reduction of insect and disease activity begins with good cultural practices including mowing, fertilization, irrigation, thatch control, cultivation practices and establishment. If an insect or disease is found to be causing serious turf damage, then a proper control method can be selected. This may or may not involve the use of a pesticide. Pesticides need only be applied to those areas where the pest is evident rather than the whole lawn.

Diseases

Diseases are defined as abnormal alterations of the internal (physiological) and/or external (morphological) development of the plant. In most cases, infectious microorganisms, called pathogens, enter the plant causing infection and symptoms to occur. Pathogens are considered the causal agents of disease.

Fungi

In turfgrass, the majority of disease infections are caused by microscopic organisms called fungi. Fungi are plants that lack chlorophyll and are incapable of manufacturing their own food through photosynthesis. Fungi produce spores (similar to seeds) and other structures that grow and penetrate turfgrass plants, often through damaged areas. Once penetration has occurred, the contents of the host cells are consumed and tissue function is disrupted. Therefore, fungi are said to be living on the organic matter of the grass (host) plant.

For a fungal disease to occur, three factors must be present. There must be a causal agent, a susceptible host and a favorable environment. This three-sided relationship has been described as the plant disease triangle. It is especially important to note that all three factors must be present at the same time for infection to take place. Prudent plant health care would suggest that anything that disrupts this three-sided relationship will prevent a fungal disease from becoming a significant problem.Cultural PracticesWhile all cultural practices can contribute to the onset of fungal diseases, variety selection, watering, mowing and fertilization practices are especially important.Disease prevention at seeding, overseeding or sodding time is much easier and also less costly than dealing with an infection in progress. The time invested in the selection of disease resistant turfgrass species and varieties will pay for itself many times over the life of your lawn. The use of improved grass mixtures is one of the best ways to prevent disease infection.Fungi require moisture (in the presence of favorable temperatures) to develop. Many fungal diseases first become active during periods of prolonged rain, or heavy dew. This condition for fungi development is greatly accentuated by poor air circulation, shade or cloudy weather. Careful attention to site selection, including tree placement, removal, or pruning, can have a continuing effect on the presence of disease. By the same token, a well-planned watering schedule can greatly reduce the length of time the grass plants are wet. Watering during early morning is better than late evening; as a general rule, deep, infrequent watering is better than shallow, frequent watering. However, where there is an urgent need for water, it is usually more important to apply the water regardless of time of day.Fertilization is the other cultural practice associated with fungal disease. Turfgrasses lacking nutrients, especially nitrogen, will be weak and susceptible. In some cases, even if disease is present, the grass plant can "out grow" the disease by growing faster than infection can occur. Unfortunately, turfgrass that is improperly or over-fertilized can have lush succulent growth that is also more susceptible to some fungal disease.It is important to maintain a mowing height appropriate for the species. Mowing heights can be raised during environmentally stressful periods or disease occurrence. Kentucky bluegrass/perennial ryegrass lawns can be maintained at 2.5 to 3.0 inches while fine-leaved fescues should be a little higher, 3.0 - 3.5 inches.FungicidesThe first step in responsible use of any pesticide product is to follow the label directions exactly as stated on the product container. The label provides necessary information regarding proper product application and container disposal procedures.Sometimes disease occurs in spite of our close attention to the cultural controls available to us. If infection is present to a degree that will cause long term damage to the turf, or is aesthetically unacceptable, the use of fungicides may be necessary.Fungicides are chemicals used to control plant diseases. Fungicides can kill or, in most cases, retard the development of the disease. Fungal pathogens are hard to control because they are one plant living on or inside another.Before applying fungicides to a lawn area, be sure that the apparent damage symptoms are being caused by a disease. Accurate diagnosis may require the assistance of a trained turfgrass professional. If a disease pathogen is found to be causing serious turf damage, then a proper control method can be selected. This may or may not involve the use of a fungicide.Fungicide applications to lawns and general turf areas are usually infrequent and, when necessary, should be applied only to those areas affected. Immediate and correct diagnosis is required as many fungal diseases progress rapidly and then require high application rates and more frequent applications. Fungicides applied to a pathogen already affecting a plant are called contact fungicides. Fungicides applied before the pathogen has affected the plant are called residual fungicides. Some fungicides are a combination of both.Properly timing fungicide applications is crucial to the overall effectiveness against the pathogen and to minimize adverse environmental impacts. Treating disease problems at very early stages of infection is more prudent and may require less total fungicide than attempting treatment of large, heavily infected areas. Normally, it is only under extraordinary conditions that a fungicide is recommended for a home lawn situation, especially under low maintenance conditions.InsectsThe number of identified species of insects has been estimated at between 800,000 and 1,000,000 of the speculated two to five million total insects. Of this tremendous number all but several hundred are considered to be beneficial. Of these, very few are serious pests of lawns.Not all 'insects' that you see in your lawn are really insects. Centipedes, millipedes, mites, spiders, and ticks are related to insects because they have an outer shell (exoskeleton) and jointed legs. Research has shown that there can be as many as 5,000 insect and insect relatives in a square foot of soil three inches deep.Life CyclesThe better you understand the insect pests in your lawn the better chance you have of managing them. There are two primary life cycles of insects that affect turfgrasses.

In complete metamorphosis the cycle includes an egg, larva, pupa, and adult stage. All young insects undergoing complete metamorphosis are termed larvae. Some larvae are also called caterpillars, maggots, or grubs. It is the adults that have the wings, legs, antennae and reproductive organs. Also, larvae and adults of a species may feed at different sites on the same plant or different plants altogether. Examples of insects that undergo complete metamorphoses are beetles, butterflies, bees and ants.

In incomplete metamorphosis the cycle includes a nymph and an adult. Both stages look the same and do the same kind of damage. Nymphs and adults usually feed at the same site on the plant. Examples include grasshoppers, crickets and boxelder bugs.DamageMuch of the damage done to your lawn happens during the larval or nymphal stage of the cycle. Many insects like webworms, cutworms, armyworms, grasshoppers and beetles do damage by chewing on leaves, stems and roots. Other insects use sucking mouth parts to rob the plant of nutrients necessary for growth and development. Examples of these insects include aphids, leafhoppers, mites and chinch bugs.Just because you notice an insect, it may not necessarily be a pest or that control is necessary. In our area, insect pests are usually less problematic than weeds or diseases. A healthy well-maintained lawn can often withstand significant numbers of insect pests.ObservationObservation is an important step in preventing insect damage. Keep your eyes open while mowing, watering and using your lawn. Make it a habit to observe your turf regularly for the presence of insect adults. Large numbers of moths or beetles can be an indication of future problems.When symptoms do occur, study them carefully. Chlorosis, (yellow tissue with green veins), dieback, wilting, or stunting can also be caused by disease, drought, compaction, or fertility problems.Inspect the soil surface, thatch layer, and root zone for evidence of pest activity or for the insects themselves. Identify the insect and its stage of development. Remember most insects are more easily controlled in the early stages of their juvenile form.Determine if the problem is significant enough to warrant control. Your local Extension Educator, Garden Center operator or Extension Service Master Gardener may be able to help you based on the number of insects you observe, the extent of damage, or other reports of damage in your area.Economic Pest Damage Threshold LevelsAlthough not used extensively with turf pests, the concept of threshold values for economic damage levels has been applied to some turf insect pests. This concept recognizes that a healthy turf can withstand a certain amount of insect damage without causing permanent damage. Even though some grass plants may be lost to the pest, a healthy turf has a relatively high degree of recoverability. After an attack, the remaining turf plants respond by quickly filling areas thinned or left open by the pest. Following are some suggested threshold values for three common Upper Midwest turf insects.

White grubs are the larvae of the common May beetle or June bug. Damage caused by these root-feeding pests appears as irregular patches of yellowed or dead grass. Heavy infestation will loosen the sod so much that it can be easily rolled back. This type of damage becomes very apparent in July and August and is caused by large (third-year) grubs. Damage caused by the smaller first- or second-year grubs is much less apparent, often making turf look wilted and water-starved.

Checking for grubs should be done from mid-June through the middle of July. Look for them by rolling back the turf from a one square foot area of suspected white grub damage. The very small first-year grubs are difficult to find and damage is relatively unnoticeable. Grubs about 1/2 inch in length are probably second-year grubs. Damage from second year grubs is usually more noticeable. The best time to control them is before significant damage occurs. Large, third-year grubs can cause extensive damage and control may not be warranted or practical. Therefore, so it's important to control them before they reach that stage. When scouting, if two to five grubs (usually curled up in a "C" shape) are found per square foot, control may be needed. Fall treatments are ineffective as grubs move down into soil for the winter.

Bluegrass billbug. If you've had a history of problems with this pest and you know what to look for (long-snouted, gray-to-black beetles with tapered abdomens and about 1/4 inch long), you may be prepared and able to treat the adult females during May when they are laying their eggs. This is the best time for control; however, it's also possible to control the immature larvae as they feed on the roots. To control the adults, apply an appropriate insecticide about 10 days after adults are sighted (about mid-May). As they mature, the small, plump whitish larvae eventually move from grass stems down into grass roots. If there are 10 larvae per square foot or more, control may be needed. Treatment is not effective after late July or early August as larvae move one to two inches into the soil to pupate.

Sod webworms are the larvae of adult moths, which are frequently called lawn moths. They feed on grass leaves at night and hide in silk-lined tunnels or burrows at night. Most of the damage is caused by the second generation. Check for them by flooding the suspected area with water to force worms to the surface for counting. This is best done in June and again in early August as there are two generations per year. If 15 or more worms per square yard are present, control may be necessary.Consult with state and local extension offices for more complete information on insect identification, life cycles, damage symptoms, and proper control practices of these and other turf insect pests.InsecticidesThe use of insecticides is necessary when damage from insect pests threatens the survival of your lawn. As with all pesticides careful attention must be directed to the safety and application information on the label. Insecticides also have the potential to cause harm to bees and other pollinating insects, earthworms and beneficial soil insects. The product selected should have the least toxic effect on the environment and only be used in those areas where significant potential damage exists.Those materials used for controlling soil and thatch inhabiting insects usually require some type of watering following application to move the product into the thatch and soil area. This puts the product where it will be the most effective, reduces the chances of it being carried away in a runoff and potentially reduces exposure to the material. While thatch can facilitate tie up of these materials and potentially reduce their effectiveness, it can also shorten their persistence in the environment.Other ControlsOne of the best times to consider insect pest control is during overseeding, seeding or sodding. Recent plant breeding has produced turf cultivars with the presence of non-pathogenic (not damaging to plants) fungi called endophytes. The presence of endophyte fungi have significantly improved resistance to webworms, billbugs and chinch bugs.At present endophyte presence is primarily in ryegrass and some fescues. However, research is being done with the other major cool season grasses to determine its presence or how it can be transferred to the desired grass species.Organic, natural and biological controls are receiving increasing attention in the research world. As these methods become effective they will provide a valuable resource in the suppression of insect pest problems. One of the most promising controls involves the application of insect pathogenic nematodes for the control of cutworms and sod webworms. For more information on managing turf diseases and insects, see:

• Turfgrass pests and beneficials