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Disease Control

Successful disease control practices involve manipulation of the environment, the grass, and/or the pathogen, to favor the health of the grass and inhibit the causal fungus.The environment can be altered in many ways, depending on the disease to be managed. For example, some diseases require free water for development. Effective strategies to reduce free water include removing dew and reducing the amount and/or frequency of irrigation. Improved air movement, drainage, thatch reduction, reduced shade, proper regulation of fertilizer applications, and good mowing practices may be appropriate methods for reducing damage from particular diseases and ensuring vigorous turf for recovery from disease damage.

When establishing new turf areas or when renovating disease-damaged turf, it is important to select grasses that are resistant to diseases known to be common in your area or that have damaged your turf in the past.The seeding of disease-resistant grass cultivars is an excellent way to minimize turf loss from diseases. For example, certain cultivars of Kentucky bluegrass are resistant to leaf spot, a devastating disease on many Kentucky bluegrass turfs. Cultivar resistance to other common diseases is available in all cool-season grasses.Another strategy is to seed a grass species that is resistant to a prevalent disease problem. For example, ryegrass may replace bluegrass in an area damaged by summer patch disease, or bluegrass might replace ryegrass in an area where Pythium blight is a problem.

Diversity in a planting almost always increases the odds of survival.

In selecting grasses for turf establishment or renovation, it is always preferable to use mixtures of different grass species or blends of different cultivars, rather than seeding a single species or cultivar. Seeding mixtures and/or blends produces a diverse population of grass plants. Such turf is usually more successful in surviving stress and attack by disease. It doesn’t take much imagination to envision what would happen in a planting of one cultivar of a single species if a disease occurred that was able to cause severe damage on that cultivar. Diversity in a planting almost always increases odds of survival.

The third method of disease control is reduction of the pathogen population by applying fungicides that will either kill the fungus or keep it from growing. Again, it is important to have identified the disease correctly, so that an appropriate fungicide can be selected. Arbitrary selection and application of fungicides without knowledge of the disease cause can do as much harm as good. Using the wrong fungicide wastes money and may involve the risk of exacerbating the disease, as well as causing other unwanted side effects.

Turfgrass fungicides can be divided into two broad categories: contact fungicides and penetrant fungicides. The contact fungicides generally are applied to the leaf and stem surfaces of turfgrasses and do not move appreciably within the plants. Hence, these materials may be washed or mowed off the leaf and stem surfaces. Consequently, they are only effective for short durations (usually 7 to 14 days) and do not protect new foliage. These fungicides are usually used for the control of foliar diseases and not diseases of the roots and crowns. In general, contact fungicides have a broad spectrum of control and have been used extensively in the turf industry for a number of years.

The penetrant fungicides are a newer group of chemicals that are absorbed and translocated within the plant.Thus, they are not as likely to be removed from the plant by rainfall and mowing. (There are several fungicides used on turf called localized penetrants, meaning that they are translocated to a lesser extent in the plant than the other penetrant fungicides.) The penetrant fungicides may protect plants for a period of 2 to 4 weeks and will protect new growth. Most penetrant fungicides can control both foliar and root/crown diseases. Penetrant fungicides tend to have a rather narrow mode of action, thus, they are somewhat prone to a phenomenon called resistance.

Resistance in fungi to certain fungicides occurs because these fungicides generally poison fungi at only a single location in their growth and development cycles. In such cases, it is possible that a small portion of the fungus population has the ability to short-circuit or get around the poisoned site and “resist” the poisoning effects of the fungicide. As these individuals reproduce, a large percentage of their offspring will be resistant to the fungicide as well. If this population grows large enough, the fungicide is no longer effective in controlling the disease and the population is said to be resistant.While resistance does not occur often, it has developed where many fungicide applications have taken place, often with repeated applications of the same or similar fungicides.To reduce the occurrence of resistance, only apply fungicides when absolutely necessary, alternate and mix fungicides with different modes of action, and use broad spectrum contact fungicides in place of penetrant fungicides whenever possible.