The cause of turfgrass damage is often difficult to determine if considerable time has elapsed between damage and diagnosis.
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. Kikuyu and Buffalo should not be cut lower than 1½ to 2 inches in a home lawn situation. 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 Kikuyu or fine-leaved couch 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.
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.
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