TG07 - TURFGRASS DISEASE NOTE NO. 7 LONG-TERM TURF MANAGEMENT PRACTICES FOR PREVENTION OF TURF DISEASES

Long-Term Turf Management Practices for Prevention
of Turf Diseases
Turfgrass Disease Information Note 7 (TGIN-007)
Henry C. Wetzel III, Extension Plant Pathologist

[Pre-plant considerations] [Established lawn maintenence]

Long-term management for disease control in lawns emphasizes good basic turfgrass management practices. These practices include the selection of the best adapted grass for the site, proper site preparation, proper management and the use of pesticides if needed.

Environmental conditions vary greatly throughout North Carolina. The northwest mountain region has a climate similar to the northeastern United States where cool-season grasses such as Kentucky bluegrass are best adapted. The southeastern region is the opposite extreme with a climate suitable for the warm-season grasses such as centipedegrass, St. Augustinegrass, zoysiagrass or bermudagrass. The region in the central part of the state is the transition zone which is often too cold in the winter for the warm-season grasses and is often too hot in the summer for the cool-season grasses to grow well. Microclimates of sites in the transition zone determines which turfgrasses are best adapted to particular lawns. The warm-season grasses are best adapted for lawns with sunny southwest exposures while the cool-season grasses are best adapted for lawns with northern exposures in this zone. The use of warm-season grasses, such as zoysiagrass or bermudagrass, for good quality turf in the summer and overseeding in the fall with cool-season grasses, such as ryegrass or tall fescue for green color in the winter can be used in highly maintained lawns with good sun exposure in the transition zone. Evaluation of the climate or the exposure of the lawn will help determine the best type of turfgrasss to grow to avoid severe disease problems in the future.

Pre-plant Considerations

Inadequate soil preparation before planting contributes to many disease problems in the future even if the proper grass is selected for the site. Most of the soils in the state have a low pH and low phosphorus levels if the area was wooded just before the lawn was planted. Soil tests should be taken from the site early enough to know how much lime and phosphorus should be incorporated into the soil before planting. The pH of many of the soils may be 4.0 or lower where trees have been growing for years. All of the turfgrasses used in the state are not native to this area and grow best in soils with a pH near 6.5 except centipedegrass which prefers a pH near 5.5. The pH scale is logarithmic which means that a pH of 4 is 1000 times more acid that a pH of 7. The soil pH determines the availability of nutrients in the soil to the plants. The soil test is often omitted and not enough, if any, lime and phosphorus is applied. These nutrients move very slowly in the soil and should be incorporated 6 to 8 inches deep before planting. Tall fescue lawns in the Raleigh area have been observed to grow well and not need any reseeding for as long as 10 years where the proper amounts of lime and phosphorus was incorporated into the soil before planting. Whereas, adjacent lawns that did not receive proper amounts of lime and phosphorus have to be reseeded yearly. The depth of incorporation of the lime and phosphorus determines the depth of rooting of the turfgrasses. A good deep and healthy root system results in a healthy plant that can better tolerate environmental stresses, compete with weeds and recover from insect and disease damage.

Time of planting, the amount of seeds and varieties of grasses used are important long-term disease management practices. The cool-season grasses grow better and conditions are less favorable for diseases if planted in the fall. The temperatures are cooler at this time and the fungi that cause many of the diseases are less active during cooler weather. High seeding rates of tall fescue, 10 pounds per 1000 square feet or more, usually result in rapid greening of lawns but often contribute to poor survival the following summer. Many small seedlings do not develop deep root systems and are very susceptible to diseases such as brown patch and drought stress. Lower rates of seeds, as low as 4 pounds per 1000 square feet, would result in slower greening of the lawn after planting but will result in stronger plants that can survive disease and drought stresses the following summer. Using mixtures of several varieties of tall fescue and mixing Kentucky bluegrass with tall fescue will help to reduce damage from diseases. The warm-season grasses should the planted in late spring or early summer to allow enough growing time for the grasses to become well established and to reduce the chances of winter damage. The national turfgrass evaluation program (NTEP) has a website (http://www.ntep.org) which helps one select turfgrass varieties best adapted for your area.

Established Lawn Maintenence

Management of the established lawn can affect damage caused by diseases. Some disease is likely to occur in all lawns sometime during the year, but a good management program can reduce the amount of damage. Fertilization based on recommendations for the specific type of grass and soil test results is the best method to use. High rates of nitrogen in the summer on tall fescue will increase the severity of brown patch. Tall fescue should be fertilized in the fall, winter and spring and not during the summer. Small amounts of nitrogen fertilizer (0.125 to 0.25 lb N/1000 square ft.) with iron can be used in the summer to improve color and may not increase susceptibility to brown patch. A lighter green color in the summer may be less acceptable to the homeowner, however, it would help reduce the severity of brown patch. Irrigation practices can affect damage from diseases. Turfgrasses in lawns should be irrigated about once a week during dry weather to wet the soil 6 inches deep. Irrigation should be scheduled between the hours of 12:00 AM through 6:00 AM to reduce leaf surface wetness which is very attractive to turfgrass pathogens. Frequent, light irrigations are not recommended since they keep the foliage wet and provides favorable conditions for diseases to develop. Turfgrasses should be mowed when the foliage is dry. Mowing when wet can spread the disease causing organisms from infected to healthy leaves more rapidly.

Environmental changes in lawns over a number of years often contribute to conditions that are more favorable for diseases and less favorable for the growth of turfgrasses. Shade and root competition from trees increases as the trees enlarge. Also, hedges become larger and thicker which reduce air movement in the lawn. The shade and reduced air movement cause relative humidity and moisture levels to remain high for longer periods on the turfgrass leaves which creates more favorable conditions for diseases. The trees and shrubs should be pruned or removed to make conditions more favorable for the growth of turfgrasses and less favorable for diseases. If trees cannot be removed, the best solution to the problem will be to redesign the landscape and use mulch or ground cover plants in the shady areas in place of grass. Homeowners often describe the problem as "I used to have a good lawn in the area", and my response is that "the trees used to be small and the turfgrasses used to have more sun exposure." The long-term solution to this problem is to decide which is more important, trees or grass, in your landscape because it is very difficult to grow good quality turf in shady areas.

Pesticides should be considered as a last resort for a long-term disease management practice. Fungicides are available that can be used to control diseases on turfgrasses in lawns. However, these chemicals will be needed frequently under favorable disease conditions, such as hot-wet weather for brown patch on tall fescue. The cost for fungicides may exceed the normal cost of a professional lawn maintenance program and homeowners must choose between this extra expense and less than desirable turf quality in late summer with reseeding in the fall. Turf quality of tall fescue will usually be acceptable in later fall with good management without the use of fungicides. Fungicides are seldom needed on warm-season turfgrasses.

Nematodes may cause serious damage on some turfgrasses growing in very sandy soils in the Eastern and Sandhills regions of the state. Good fertility and irrigation practices are the only methods available to help overcome the damage from nematodes in home lawns. Chemicals are not labelled for use in home lawns to control nematodes.

Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemcial will not always conform to the safety and pest control standards indicated by experimental data. All recommendations for pesticide use were legal at the time of publication, but the status of the registration and use patterns are subject to change by actions of state and federal regualtory agencies. 07/92/1000

Published by North Carolina Cooperative Extension Service
Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

Reformatted Dec. 2000 by Plant Disease and Insect Clinic