How To Keep Turf Grass Healthy

C. L. Lefebvre, F. L. Howard, Fred V. Grau.

The 20 million acres of turf and 20 million lawns in the United States are prey to 100 different disease-producing organisms. Large sums are spent each year to establish good grass on golf courses, lawns, parks, and playgrounds, but the results are often disappointing. The main reason lies in the fact that the grasses that compose turf are subjected to unnatural conditions. When man first mowed grasses closely to produce turf for specific purposes, the possibilities of disease incidence were multiplied.

Turf is so commonplace that little attention has been given to its proper maintenance. However, cutting the grass blades wounds the plant and reduces its ability to manufacture food. The lessened supply of food and repeated injury make the plant more susceptible to attack by pathogenic micro-organisms. The grass that grows normally may be attacked by the same diseases, but it is better able to recover because it has a full leaf system. (An exception is the bentgrasses, the mowing of which makes for a healthier and better turf, while longer cutting causes matting, more disease, and actual smothering of the plants.)

Natural selection, operating over a long time among the closely mowed mixed grasses, has given us types or Species of turf grasses that are better able to survive diseases and to recover from injuries with greater vigor.

Many of the common pasture grasses, which grow more normally, never have been called on to survive repeated clipping. Sometimes a turf grass and a pasture grass may be the same, yet disease control measures applicable to lawns and golf greens are not feasible on pasture grasses that are grazed continually.

Diseases of turf are parasitic or non-parasitic.

Fungi cause the main parasitic diseases. Fungi usually are more destructive to grass plants that produce what is considered a good, dense turf. At their leaf tips, the rapidly growing plants secrete drops of water of guttation, which encourage the quick development of the fungi. Moreover, the densely growing plants shade each other and tend to hold moisture longer, as there is less chance for evaporation of the surface moisture. Because water is essential for germination and growth of the spores and other reproductive structures of fungi, conditions that favor air circulation and the removal of water films from the grass blades also help to control disease.

Upper left: Dollar spot injury of creeping bent, caused by Sclerotinia homeocarpa. Upper right: Leaf spot injury of Kentucky bluegrass, caused by Helminthosporium vagans. Lower left: Fairy ring, caused by the mushroom Marasmius oreades. Lower right: Brown patch injury on Colonial bent, caused by Pellicularia filamentosa.

Temperature may markedly affect the development of both the grass plant and the fungus parasite. The bluegrasses and fescues grow best in the cooler temperatures of early spring and fall, for example, and grasses like Bermuda-grass and Zoysia species thrive best at summer temperatures. Similarly, the fungus that causes the destructive dollar spot disease thrives at temperatures below 80 F., but the brown patch fungus is much more injurious at temperatures above 80 .

The nonparasitic, or physiological, ailments injure a plant through unfavorable nutrition, moisture, light, temperature, soil reaction, or some chemical that has been added to the soil. For normal growth, plants must have the essential nutrients in proper balance. Acidity or alkalinity of the soil must be adjusted to suit the requirements of the grasses. Frequently in alkaline (or "sweet") soil, iron is not absorbed sufficiently, so that an application of iron sulfate gives a better green color. Heavy applications of fertilizer, especially when the grass blades are wet, often causes burning of the turf. The use of chemicals to control weeds frequently reduces the vigor of desirable turf grasses and provides a suitable medium for fungi. An oversupply of water in the soil excludes oxygen, which the roots need. Too much water also promotes the development of pathogenic fungi that attack the grass roots weakened by lack of oxygen.

PROPER MANAGEMENT, based on knowledge of the physiology of grasses and their cultural requirements, can do much to reduce the severity of diseases. Even if the recommended practices do not cure a disease, they may curb it so that chemical controls can be more effective.

Because the fungi need moisture, proper drainage of turf areas to prevent excessive accumulation of moisture helps to control diseases.

Aerification of compacted soils helps water and air to reach the roots of grasses. Aerifying the soil also releases trapped air, removes excess surface water, and seems to free certain nutrients by changing the degree of acidity and alkalinity. Any practice that encourages vigor is good, for a rapidly growing, vigorous plant often is better able to withstand a disease or to recover more speedily.

Lime and fertilizers at the proper time and rate may alleviate the effects of the diseases. Technicians at the Georgia Agricultural Experiment Station learned that 2 pounds of nitrogen to 1,000 square feet, applied a month before seeding or at seeding time, reduced the occurrence of dollar spot in ryegrass. Research at Pennsylvania State College disclosed a striking inverse relationship between the application of nitrogen and the prevalence of dollar spot.

Practices that provide for good seedbed preparation, proper rate of seeding, adequate air and drainage, and the height of cut recommended for a particular species or strain of grass are other management practices that will retard disease. For example, in 1951 the workers in Georgia found that injury from diseases was much greater when ryegrass was sown at 100 pounds than at 40 pounds to 1,000 square feet.

IT'S A GOOD THING to grow grasses that are resistant to disease. That is easier said than done, though, for it is hard to find and develop grasses that have high disease resistance and the required agronomic characteristics. Newly developed strains of grasses may retain resistance for only a short time, because new strains of fungi may develop.

Washington, Cohansey, and Arlington bents are much more resistant to brown patch than is Metropolitan. Seaside bent is moderately susceptible. Colonial is very susceptible. Washington bent, however, is very susceptible to dollar spot, as is the Toronto strain. Elk 16, Arlington, Congressional, Highland, Seaside, and velvet bents appear to have resistance to the dollar spot fungus. Congressional bent has shown resistance to snow mold.

The leading vegetative selections of creeping bentgrasses in use in the United States in 1953 included these strains, arranged in approximate order of their resistance to the more common diseases: Dahlgren (C-115, according to the numbering system used by the Green Section to designate creeping bents); Arlington (C 1); Congressional (C-19); Old Orchard (C-15); Cohansey (C-7); and Toronto (C-15).