Penn State Department of Plant Pathology & Environmental Microbiology Archives, Penn State, Bugwood.org
A careful diagnosis involves analysis of climatic and environmental conditions, along with the management program followed. It is important to know what fertilizers, insecticides, fungicides, or herbicides have been applied, the amounts used, and the time and method of application.
Height of Cut
Mowing is one of the most abused and least understood turfgrass management practices. Kentucky bluegrass and fine-leaved fescues should not be cut lower than 1½ to 2 inches. Shorter mowing reduces leaf surface (the plant's food manufacturing factory) to such a degree that the plant may have to draw food from its root reserves to initiate new growth. Repeated defoliation reduces the root system, and the plant will be weakened and unable to cope with adverse weather conditions.
Frequency of Cut
Infrequent mowing, which has become increasingly common with the popularity of the rotary mower, may remove excessive amounts of clippings at each mowing. This may shock plants, causing depleted root reserves and general weakening. Normally, no more than one-fourth to one-third of the total leaf surface should be removed at each mowing. Excessive clippings left on the turf may injure or kill turf by smothering it. Hot, humid conditions under these clippings are ideal for disease development.
Turf may have a gray to brown cast following mowing. In most cases this discoloration can be attributed to dull rotary mowers, although reel-type mowers may cause the same kind of damage. Basically, the discoloration is due to tearing, splitting, or shredding of the tips of the grass blades. Always keep any mower sharp and properly adjusted.
Most scalping occurs when attempts are made to cut steep terraces crossways rather than up and down the terrace. Scalping may also occur on poorly graded areas where one wheel of the mower may drop into a surface depression, resulting in a closer cut on that side of the mower.
Turfgrass areas regularly cut with power mowers sometimes develop wave-like ridges running at right angles to the direction of mowing. This washboard effect may be prevented by regularly changing the direction of mowing. Alternating directions of cut will partially control runners of creeping grasses and help prevent grain and thatch.
Although fertilizer skips do not constitute actual damage, they do result in a very unsightly appearance. The fertilized area will be a brilliant green, whereas the unfertilized area may vary from pale green to a chlorotic yellow color. Since fertilizer materials seldom move laterally, every effort should be made to distribute the material uniformly over the entire area.
Any type of fertilizer may cause fertilizer burn if applied in excessive amounts or when grass blades are wet. Soluble forms of nitrogen and potash are most likely to cause serious burn. To avoid this problem, always apply fertilizer in recommended amounts when grass is dry; if at all possible water thoroughly after application.
Turf areas may become pale green-yellow, and plant growth may be somewhat stunted. In most cases this chlorotic condition is due to lack of nitrogen. If a nitrogen fertilizer application does not correct this condition, it is very likely that the cause is iron deficiency. An application of iron sulfate or chelated iron on turf showing iron deficiency will result in a greening of the turf within a few hours after application.
Some weed killers used to control specific weeds may damage turfgrasses if applied at rates exceeding recommendations. Unfortunately, many people feel that if "X" ounces of material per 1,000 square feet is recommended, "2X" ounces of material per 1,000 square feet will do a better job. The result—turfgrass injury or death. Always apply herbicides accurately at the manufacturer's recommended rate.
Irrigating a turf area at a rate greater than the soil's infiltration capacity may have deleterious effects. This type of watering causes run-off and wastes one of our most expensive commodities—water. More important, a thin surface crust may form. This crust will impede the entrance of nutrients, insecticides, air, and water into the soil. Such a crust also favors development of weeds such as moss and algae.
Turfgrasses may also be damaged by frequent light watering. Frequent shallow watering may keep upper soil layers near a constant saturation point. This condition encourages shallow rooting and promotes weak turf which is susceptible to disease and insect attack as well as damage from traffic. For most turfgrass areas watering deeply only when plants show signs of wilting is a sound watering program and a big step forward in the development of healthy, vigorous turfgrasses.
Localized Dry Spots
Dead or injured spots often develop in turf areas because of insufficient moisture, even though surrounding turf shows no drought injury. Buried debris such as stumps, stones, bricks, or gravel may result in a thin layer of soil overlaying the area. This soil layer has a low water-holding capacity and dries out very quickly. In other cases a large amount of thatch may act as a thatched grass roof preventing water infiltration into the soil.
Foot Printing of Turf
In hot weather heavy foot printing of Kentucky bluegrass or fine-leaved fescue turf usually indicates that the turf has reached the wilting point and must be watered to maintain green color. When irrigating, wet the soil deeply; then refrain from watering until the turf again approaches the wilting point.
A different type of foot printing may be observed in late winter or early spring. The turf may be injured if it is walked on when grass blades are frozen or heavily frosted. Under these conditions walking may rupture frozen plant cells and injure or kill the plants.
Often referred to as winterkill, desiccation is most likely to occur during late winter months. Damage is most prevalent on high, exposed areas which frequently hold little snow cover and are subjected to strong, drying winds. In late winter the soil often thaws to a depth of 1 to 2 inches; air temperatures are favorable for grass growth, but roots imbedded in still frozen ground are unable to take up enough water (if any) to satisfy the plant's transpiration rate. The turf, therefore, dies from lack of moisture.
Turf often appears burned out over septic tank areas. This may occur when the septic tank is not buried deep enough to allow several feet or more of soil over the tank. Consequently, the soil dries out quickly. Drying is often accelerated by heat from decomposition in the tank.
Annual bluegrass (Poa annua) is normally considered an annual grass, although some plants may survive longer than one growing season. Annual bluegrass has a light yellow-green color and is characterized by prolific seed production in the spring. Regardless of height of cut, this plant will develop seeheads. Due to the great number of seedheads, areas heavily infested with annual bluegrass take on a gray-white cast in the spring. Annual bluegrass is shallow-rooted and cannot withstand high temperatures combined with either severe drought or saturated soil. Under these conditions the grass may die in a few hours. Unfortunately, because seed produced in the spring has been deposited in the soil, a new crop will germinate in fall or late winter. Thus, an annual bluegrass-infested turf may appear beautiful in spring and late fall but may be unsightly in summer. Provided the infestation does not exceed 40 percent of the total turf population, annual bluegrass can be reduced by applying bensulide (Betasan or Pre-San) according to manufacturer's recommendations for two consecutive years. After this, no applications should be made for one to two years.
Management practices for bentgrass (which is often found in commercial seed mixtures) and Kentucky bluegrass are not compatible. Bentgrass requires close, frequent mowing, frequent fertilization and irrigation, periodic topdressing, vertical mowing, and a regular preventive fungicide program. Fluffiness of the turf is usually associated with a high bentgrass population. Unless bentgrass is managed intensively, it will develop a thatch layer quite rapidly. Once a turf has become infested with bentgrass, the only solution is to kill all vegetation with a grass weed killer and reestablish the lawn to desirable grasses.
Although many individuals regard crabgrass as the number one turf problem, there are a number of effective preemergence chemicals to control it. Apply these materials in the spring approximately two weeks prior to expected crabgrass germination. Crabgrass normally germinates when soil temperatures near the surface reach 60°F. DCPA (Dacthal), benefin (Balan), bensulide (Betasan or Pre-San), and siduron (Tupersan) are materials recommended for pre-emergence control. Restrict the use of DCPA and benefin to Kentucky bluegrass turf. Remember that crabgrass seeds may lie dormant in the soil for many years, requiring a long-range concentrated control program. The publication "Crabgrass Can Be Controlled", available in your county agricultural Extension office, contains more information on crabgrass control.
A coarse-bladed perennial grass having excellent wearing qualities, tall fescue is used extensively for play fields, utility turf, and other areas subjected to heavy use and/or minimum maintenance. For best results it must be seeded alone at rates of 8 to 10 pounds per 1,000 square feet. Tall fescue is often a component in poor quality turf seed mixtures. When used in mixtures, individual plants may stool out, smothering other grasses and making mowing difficult. There is no selective chemical means of eradicating these plants. Control tall fescue by hand digging or spot treatment with a non-selective contact herbicide followed by reseeding the treated area.
Rough bluegrass is often a contaminant in Kentucky bluegrass seedlots, especially in seed imported from Europe. In established turf it appears as light green patches with the grass blade having a shiny, glass-like appearance. In open sun, it normally dies back severely during hot weather but may recover somewhat during cool weather where stolons are protected. Rough bluegrass is excellent for use in wet, shaded areas but should not be seeded in open, sunny areas.
A weed grass often mistaken for desirable turfgrass especially in the spring, nimblewill develops in patches, spreading by decumbent stems. It normally turns brown much earlier in the fall and in spring turns green later than desirable turfgrasses. Under mowing it often becomes quite stemmy, and thrives best under conditions of low fertility. There is no selective chemical control, but a good over-all maintenance program (lime, fertilizer, pest control) will help keep down infestation.
Many people feel clover is desirable in a turf area, but turf specialists and those involved in maintaining specialized turf areas such as golf courses or athletic fields do not. Clover often segregates into unsightly patches, is slippery and provides poor footing, has low wear resistance, may be severely winter-damaged, and forms seasonal white blossoms which interrupt the continuity of the turf and attrack bees. To eliminate clover, apply MCPP or dicamba (Banvel).
Weeds such as dandelion, broadleaf plantain, and buckhorn (narrowleaf plantain) are easily controlled with 2,4-D. More difficult to control broadleaf weeds such as knotweed, chickweeds, heal-all, henbit, stitchwort, and sheep sorrel may require the use of 2,4-D plus dicamba. Some, but not all, species of Veronica may be controlled with this combination.
Moss and Algae
Moss and algae seldom invade a dense, healthy turfgrass area. Infestations are usually associated with low soil fertility, poor drainage, high soil acidity, improper watering, too much shade, soil compaction, or a combination of these factors. Diagnosis of the cause or causes of infestation followed by corrective measures is the best control.
Disease and Fungus
A number of leafspot diseases are particularly severe on many Kentucky bluegrasses and fine-leaved fescues. The most obvious disease symptoms are circular to elongated spots on the leaves. These spots have brown or straw-colored centers and prominent reddish-black to brown borders. Leaves, stems, crowns, and roots may be affected, often causing considerable thinning of the turf. These diseases first occur on the leaves during cool, wet weather. If not checked by changes in weather conditions or application of chemical fungicides, the disease may move into the plants' crowns and roots, causing considerable damage throughout the entire summer. For recommendations on leafspot control contact your county agricultural Extension office.
Some Kentucky bluegrass varieties are extremely susceptible to Fusarium blight, especially if nitrogen availability is high. The disease occurs most frequently during hot weather when the plants are under moisture stress. Circular to irregular patches of light green grass, 2 to 8 inches across are the first symptoms. These patches quickly turn to a reddish-brown, then to tan, and finally to a light straw color. Plants normally die during the reddish-brown stage. Apply systemic fungicides immediately after first symptoms appear to reduce disease severity.
In late summer, powdery mildew often develops on Kentucky bluegrasses, especially Merion Kentucky bluegrass growing in shaded areas. Although the white powdery substance deposited on the leaves is unsightly, it normally does not cause serious damage unless it persists for a long time. Powdery mildew can be controlled with Acti-dione fungicide applications, although the best solution is to plant more shade-tolerant grasses in these areas.
Although it attacks many turfgrasses, stripe smut is most severe on some varieties of Kentucky bluegrass, especially Merion Kentucky bluegrass. It is caused by a systemic fungus that attacks grass internally, in contrast to most turfgrass disease fungi that attack plants externally. Initially, stripe smut-infected plants appear light green to yellow-green and soon develop light green to gray streaks on leaves and sheaths. As the fungus develops, the epidermis over these streaks ruptures, releasing a mass of black smut spores. The leaves then split and curl and eventually die. Most severe damage usually occurs during cool periods of spring and fall. Apply preventive fungicides in late fall or early spring to reduce disease severity in the spring.
A common fungus disease that normally is most severe on fine-leaved fescues, red thread may also attack Kentucky bluegrasses, ryegrasses, bentgrasses, and some warm season grasses. In early morning or when humidity is very high, the grass plants may be covered with a gelatinous mass of pink mycelium that mats the leaves together. As this gelatinous mass dries, hardened pink to red threads of the mycelium may protrude from the leaf tips. Infected leaves first appear water-soaked, rapidly fading to a bleached tan as they die. Red thread usually occurs when temperatures are 60° to 75°F and humidity is high. Red thread is also most severe under conditions of low fertility. Fungicides coupled with adequate lime and fertilizer will control this disease.
Rust appears as reddish-brown to black pustules on grass blades or stems. When severely rusted turf areas are walked on or mowed, a cloud of red powder composed of spores may arise. Rust is often found on Merion Kentucky bluegrass during late summer months. Although unsightly, rust normally will not cause serious damage if the turf has been well fertilized.
Fairy rings may appear as mushroom rings or as dark green rings of vigorously growing turf varying from a few inches to many feet in diameter. Fairy ring is caused by fungi living on decaying organic matter such as stumps, logs, or scrap lumber from building construction buried in the soil. The fungus grows out radially. Nitrogen from the mycelium of the fungus is released, stimulating growth and causing a dark green ring. During dry periods this stimulated succulent growth may die from lack of moisture. There is no effective chemical control. During dry periods keep the fairy ring well watered to prevent loss of turf from moisture stress.
Slime molds are nonparasitic fungi that live on decaying soil organic matter. During wet summer periods these fungi develop on grass blades, forming yellow to gray jelly-like structures which later mature into gray to black spore masses. These masses may damage the grass by shading or smothering. Normally, slime mold will disappear during dry weather. Brushing infested areas with a stiff broom will at least temporarily remove the unsightly condition. If wet weather favorable to slime mold persists, control the mold by applying any good turf fungicide.
Toadstools and Mushrooms
Heavy infestations of toadstools and/or mushrooms often occur in turfgrass areas. These are saprophytic fungi living on dead organic matter in the soil. They are most prevalent where trees have been removed without complete removal of the tree roots. There is no adequate control, and these organisms will continue to appear, especially during wet periods, as long as there is adequate organic matter in the soil.
Gray snowmold, a true snowmold, occurs under snow cover. The affected grass forms a mat or crust of leaves a few inches to many feet in diameter and may show a white to gray mold with tiny black fruiting bodies (sclerotia) imbedded in the leaf tissue. Thorough brushing or raking to break this crust usually results in grass recovery. Pink snowmold occurs when the temperature is approximately 40 to 60°F and abundant moisture is available. Pink snowmold is more damaging than gray snowmold and often results in death of the turf. To control snowmolds fungicides must be applied in late fall or early winter and again in early spring. Consult your county agricultural Extension office for the latest recommended control materials.
Yellowish spots that rapidly turn into brown, dead areas may be an indication of chinch bug damage. Chinch bugs are sucking insects which concentrate in limited areas and feed on the plants until they extract all available juice. The bugs then work outward from the centers of infestation, destroying grass as they advance. Chinch bugs develop best in dry weather, and injury is always more severe in hot, dry summers. They prefer high, dry locations exposed to direct sunlight. Chinch bugs can be controlled by repeated applications of diazinon, Aspon, or chlorpyrifos (Dursban).
Grubs of the Japanese beetle, May or June beetle, northern masked chafer, European chafer, green June beetle, Oriental beetle, and Asiatic garden beetle may severely damage turf. These grubs feed on roots of the grass and when abundant may completely sever the turf from the soil so that it can be rolled up like a carpet. Grubs can be controlled with chlorpyrifos, diazinon or trichlorfon (Dylox, Proxyl). In severely damaged areas the severed turf should be raked off prior to insecticide application and reseeding.
The presence of small, buff colored moths flying above the turf in a zig-zag pattern during the evening hours is a sign of sod webworm infestation. The moths, harmless to turf, are the adult stage of the webworm; immature larvae and the webworm caterpillars damage the turf. The sod webworm constructs "silken lined" tunnels in the soil; webworms emerge during the evening or night to feed by clipping off grass blades at the soil surface. During the daylight they hide in the tunnels. The first symptoms of damage are small irregular patches of dead grass which enlarge as damaged areas coalesce. Carbaryl (Sevin), chlorpyrifos, or trichlorfon applied in late afternoon or early evening will control sod webworm.
Turfgrass areas infested with mole runs or tunnels become unsightly, uneven, and difficult to mow. Contrary to common belief, attempting to kill the moles by poison bait or mole traps is not the best solution. The moles are there because the soil is infested with grubs, a favorite food. Treatment with an approved insecticide for grub control will cause the moles to abandon the area as their food source is exhausted.
Skunks may damage turf by rooting for grubs. The solution, as in mole control, is to eliminate the grubs with an appropriate insecticide.
The effect of dog urine on turfgrasses depends upon the amount of soluble salts in the urine. When soluble salt concentration is high, turf in the affected area will be killed. Damaged areas are usually round or slightly irregular in shape and variable in size. Nitrogen from urine with lower salt concentration may stimulate vigorous dark green growth.
During periods of heavy snowfall (particularly if snow comes before the soil is frozen) mice may make runways in the turf under the snow. These runways are on the surface of the turf rather than under the turf as with moles, and normally are most severe in heavily matted turf where snow tends to accumulate in pockets. Mice have been known to feed on tender plants along the run.
Soils of poor physical condition or those subjected to play or heavy traffic (especially when wet) form an impervious surface layer which prevents water infiltration, nutrient penetration, and gaseous exchange between the soil and the atmosphere. Under these conditions turfgrasses may thin out and be replaced by weeds such as knotweed, which flourish on compacted soils. Aerating machines will remove soil plugs or cores, creating an artificial system of large pores which will permit moisture, nutrients, and air to enter the soil and alleviate the compacted condition.
Damage from winter scald may occur where poor drainage permits ponded water to freeze. Heat from the sun shining through this layer of ice can initiate growth. As no gaseous exchange can occur through the ice, some turf may die. The only solution is to correct the drainage problem.
Poorly drained areas subject to water ponding for short periods may be seriously damaged by scald. Summer thunderstorms may release large amounts of water in a short period; if the storm is followed by clearing and a hot sun, the sun's action on the ponded water will produce anaerobic conditions which cause the damage. As with winter scald, the only practical solution is to improve drainage.
Layers of partially decomposed leaves, stems, and roots at the soil surface will build up over a period of years. Thatch decreases turfgrass vigor by restricting the movement of water, air, fertilizers, and pesticides into the soil. Roots are normally quite shallow under thatch conditions, increasing the danger of drought damage to the plant. Disease attacks may be accentuated by thatch accumulations. Mechanical thatching equipment should be used in spring or fall when grass recovery is rapid. It is best to remove thatch accumulations in several treatments rather than at one time.
Trees, especially those with shallow feeder roots, compete with grass for water, nutrients, and light. Where there is heavy shade and/or many surface roots, it is best to plant a ground cover such as pachysandra, myrtle, or ivy rather than attempt to grow grass. Where competition is less severe, improve turf by the following methods: (1) use shade-tolerant grasses such as the fescues and Poa trivialis; (2) fertilize grass at 1½ to 2 times the normal rate; (3) fertilize trees; (4) water deeply and infrequently; (5) maintain a soil pH favorable to the grass; (6) prune tree branches and roots as much as possible; and (7) mow the grass higher than normal.
Many turf problems can be traced to the original seed mixture - either a poor quality mixture, or a mixture not appropriate for the particular area. For example, grasses such as common ryegrass, timothy, and redtop normally will not persist under normal management. Kentucky bluegrasses are unsatisfactory for use in shaded areas but are excellent in open sun. Fine fescues are well adapted to shade conditions. Tall fescue, when seeded alone, is an excellent play field or utility grass but should not be used in seed mixtures. Bentgrass requires intensive management and, therefore, is not compatible with Kentucky bluegrass and fine fescues. Select a grass seed mixture according to environmental conditions, use of the area, and the planned management program.
Gasoline and Oil
Servicing or refueling power mowers or other power equipment on the turfgrass area may cause considerable damage from gasoline or oil spillage. Because it is not immediately apparent, this type of damage may be incorrectly diagnosed as disease, insect damage, or dog injury. If the soil is saturated (especially with oil) it may be some time before reseeding will be successful. To avoid the problem always service or refuel power equipment off the turfgrass area.
Turf damage often appears in late winter or early spring in grass plots between the sidewalk and the street. Frequently this damage is due to high soil salt concentration from salt materials used for de-icing highways and streets. The same type of damage may be found adjacent to sidewalks if salt or a soluble nitrogen fertilizer has been used for ice control. Normally, spring rains will leach salt concentrations below the grass root zone, permitting reseeding of these areas.
Prepared by Peter J. Landschoot, Professor of Turfgrass Science.