Practical Solutions: Disease Management

Lawn care operators (LCOs) who care for turf with little or no problems usually have developed the art of turfgrass management for the specific turfgrass species they grow. Proactive daily management decisions have to be made and modified based on ever-changing environmental conditions and disease-causing factors. But the key to disease control is a healthy plant. Turf must be managed and soil should provide the best possible growing conditions for optimum turf health.

FUNGI FACTS. Fungi are a natural component of our ecosystem. Most are saprophytic (feed on dead organic matter) and without them we would be up to our armpits in leaf litter and thatch. Many of the turfgrass, disease-causing fungi fall in this category (Rhizoctonia solani, Helminthosporium sp., Curvularia sp., Colletotrichum sp., Pythium sp. and Pyricularia sp. to name a few). They are beneficial, but can cause disease when the turfgrass species is weakened or the environmental conditions stimulate the fungi to be more aggressive. This means that they are always present in the soil where turf is grown. No matter what lawn care operators do to eliminate these fungi, they cannot.

DIAGNOSING DISEASES. LCOs have to inquire about certain factors to find disease-causing catalysts. By looking at a diseased lawn that is located next to healthy turf, LCOs can learn management recommendations for disease control. By looking at stimulants that activated fungi or weakened turf, LCOs can come up with a fairly accurate diagnosis – at least good enough to initiate or revise a management program.

Some common questions to ask when attempting to diagnose diseased turf are: When was the last time the turf was fertilized, what was the formula and how much was applied to the property? What are the watering practices for the turf? What pesticides have been applied to the turf area? Describe the location of the damaged area (shade, sun, low area, under trees, etc.). When did you first notice the problem? How has the problem area developed since the moment that it was first observed?

WATERING & DISEASE. Watering is one of the most frequently abused practices. Turf that isn’t watered properly can become unhealthy and diseased. Because of the diversity of soils throughout the United States and the different types of grasses being grown, making specific recommendations for proper irrigation is difficult. However, there are improper watering practices to remember and ways to determine how much water is being applied that contractors should keep in mind.

Regardless of geographic location, there are times when an LCO does not want to water – any time that it will extend the leaf wetness of the natural dew period, for example. If the dew falls at 8 p.m. and the turf does not dry off before 10 a.m. the next morning, the turf foliage is wet for about 14 hours. This is not enough constant wetness for any significant disease to occur. If the turf is watered at 4 p.m. and an extra four hours is added, totaling 18 hours of leaf wetness, disease fungi can infect turfgrass and cause significant damage.

The key is to water early enough during the day so the turf foliage can dry before dark. This breaks the infection cycle because turf has to accumulate successive hours of wetness again to cause infection. Most homeowners do not know this and informing them can help lawn care operators manage turf.

To determine the amount of water being applied on turfgrass, LCOs should get several 9-inch, straight-sided cake pans and place them randomly under the sprinkler or irrigation system. Turn the water on and time how long it takes to fill one of the pans, which amounts to about 1 inch of water. This indicates how long the irrigation system should be left on to accumulate 1 inch of water. Plus, this test also helps LCOs determine whether or not any problems with even water distribution exist in the area being irrigated.

THATCH & DISEASE. In many turfgrass species, fungi can survive long periods of time in excessive thatch, which provides a food base for fungi to survive. Most fungi that cause disease are good saprophytes and decompose organic matter. In addition, excess thatch can lead to a shallow turf root system if the thatch is kept too wet and moisture cannot penetrate the soil.

Essentially, excessive thatch is like a sponge. It will dry out quickly, and well-developed turf roots will weaken during drought. Therefore, watering to overcome dry conditions and then wetting the thatch promotes shallow roots. The thatch soaks up water and water will not move into the soil profile until the thatch is saturated. Fertilizers and pesticides also are bound into the thatch promoting a shallow root system.

To determine how wet or moist the soil is and to get a feel for the root system and thatch development, probe the soil profile with a soil test tube. In addition, know the turf being managed and follow local recommendations on the allowable thatch for that turf species.

Aerification and de-thatching are sometimes recommended to alleviate thatch problems, but these practices have limited impact unless initiated during early thatch development. Once too much thatch has established, there is little that can be done short of extensive turf renovation.

If a thatch problem exists on a lawn, determine if the problem developed because of excessive fertilization and/or improper watering practices. Correcting these management practices will reduce the potential for future disease.

CONTROL OPTIONS. For years, the control perception has been control equals eradication. This is not true. Control means reducing economic or aesthetic loss caused by the fungus or levels of fungus. The fungi are still in the turf area – they will always be there doing their ecological feeding to recycle organic matter. However, LCOs should be able to manage the turf with relatively little, if any, disease problems by knowing the turf type and providing the best possible pH, nutrition and timely mowing practices with sharp blades that don’t impose excessive physical stresses or damage to the turf.

Fungicides should be used as helpers after other management practices have been initiated. Fungicides are agri-medicines that kill fungi in various ways. They should not be relied upon entirely for disease control. Every now and then, Mother Nature steps in and provides conditions favorable for disease. In these cases, we see widespread disease that is not associated with anything we have done, so we do the best we can to manage turf out of stressful conditions.

The bottom line is that the fungus that causes disease problems and the fungicide used to control that problem are just two pieces of the puzzle. The other components of the issue are environmental and management related. Once these factors are identified, LCOs are well on their way to resolving the problem, not just temporarily but for a significant length of time.