Fact Sheets And Publications

Turfgrass Disease: Best Management Practices for Delaware

In Delaware, turfgrass diseases are caused by pathogenic fungi and microbes that infect the leaves, stems, and roots of turf type grass plants. With infection, grasses may show symptoms such as leaf spots, mildew or mold, or patchy dead areas. Fungi and microbes that cause lawn diseases are naturally present, but disease occurs when environmental and cultural factors favor growth of a pathogen and increase the susceptibility of the grass host. In order to manage diseases in landscape and athletic turf, it is important to understand the dynamic interaction among pathogens, grass plant hosts, and the environment. Overall health of a lawn is influenced by cultural management strategies.

Management Practices that Reduce Disease

Turf selection. When establishing a new lawn or turf area or renovating an existing one, select a turf species or mixture of species that is adapted to the site conditions and the level of traffic or use, and for management practices that you are willing to do. Delaware is in the transition zone where the cool-season grasses (Kentucky bluegrass, perennial ryegrass, tall fescue, red fescue) are stressed during hot, dry summers, and the warm season grasses (Bermuda grass and zoysia grass) turn brown after a frost and can be invasive. Turf-type tall fescue is well adapted for many lawn and landscape sites, and requires less fertilizer than bluegrass, ryegrass and fine fescues. It can be seeded or sodded. Turf-type tall fescue sod contains approximately 10 percent bluegrass for sod root strength. Perennial ryegrass can be added when seeding for quick germination, because tall fescue is slower to germinate. High quality seed and sod blends are available from reputable suppliers. Specific turf types for golf course and athletic field use are more unique selections.

Soil and fertility management. Soil conditions including fertility are the basis for establishing and maintaining lawn or landscape turf successfully. A balanced fertility program derives from a soil test every 3 to 5 years or before seeding a new lawn. Balanced, adequate nutrient levels will improve the vigor of plants, which in turn aids with resistance to disease. Establishing lawns on new construction sites where topsoil may have been removed or only a thin layer is present is particularly difficult. The addition of organic matter in the form of topsoil, leaf mold, compost, or other source is recommended. Soil compaction can be a problem in a newly constructed landscape as well as in older lawns or turf with high traffic or athletic use. Compacted soil excludes air and impedes water movement, which reduces root function, and results in a decline in plant vigor and disease resistance. In new lawns, it is important to prepare soil well. The seed bed should be firm but not compacted. In established lawns, core aeration will relieve compaction and reduce thatch accumulation.

Nitrogen is the most significant nutrient that influences disease severity. Excessive applications of soluble nitrogen can favor diseases such as brown patch, Pythium blight, and leaf spot. Succulent grass has thinner cell walls, which are more easily penetrated by microbes. Conversely, turf grown in nutrient-poor soil can be prone to dollar spot, rust diseases, and red thread. In this case, light applications of nitrogen will stimulate grass species to produce leaves and turf may “outgrow” the pathogen. Generally, nitrogen should be applied in fall or early spring, with most lawns requiring 2-3 pounds of actual nitrogen per 1,000 sq. ft. per year. Kentucky bluegrass lawns are heavy feeders and require the high rate, while tall fescue lawns do well with the suggested rate.

Mowing. Regular mowing is necessary to maintain quality turf. Mowing may favor microbial infection by creating wounds and, in some cases, disseminating pathogens. Height of cut also influences disease susceptibility. Mowing too closely predisposes turf to several diseases by removing the young leaf blades most active in photosynthesis. This causes a depletion of food reserves in the plant, which are necessary for vigor, disease resistance and recovery from stress and injury. The “1/3 Rule” suggests to remove no more than 1/3 of the leaf blade height at one time. Keep mower blades sharp. If mowed regularly, clippings can remain on the lawn; they do not contribute to thatch and can return nitrogen-rich material back to the lawn. Turf utilized for sports such as golf may be more challenging due to height specifications.

Water management. Proper use of irrigation can aid in management of turfgrass diseases. Frequency, timing, and duration of irrigation are important factors in predisposition of turf to diseases. Water is necessary for spore germination and microbial growth, and excessive water encourages succulent turf, prone to infection. Waterlogged soils are not well aerated and root growth is poor. Algae and mosses thrive in waterlogged soils, where turf density is poor. Droughty soils predispose turf to some pathogens. Irrigate deeply but infrequently to avoid drought stress, which maintains turf in good vigor and reduces the impact of diseases. In the summer, morning is the preferred time to irrigate so that turf has a chance to dry by nightfall. Irrigation systems on automatic timers may result in excessive water during periods of rainy weather.

Thatch management. Thatch accumulation of more than ½ inch can restrict root growth and predispose turf to water stress and disease. Many turfgrass pathogens can survive as saprophytes in the thatch layer. Summer patch, leaf spot, and melting-out diseases are a few of the diseases favored by excessive thatch accumulations. Regular core aeration in the spring or fall will reduce thatch accumulation and open compacted soils.

Nancy Gregory

Plant Diagnostician

9/17/2018

Disclaimer: Reference to commercial products or trade names does not imply endorsement by University of Delaware Cooperative Extension.