12. Disease management

OBJECTIVE: Monitor and manage pressure and infection from turfgrass damaging diseases. 

Set action thresholds for disease occurrence on a particular site. 

• Disease pressure and incidence are often significantly lower on lawn turf than on other more closely cut and more intensively managed areas, such as golf courses. 
• Common lawn diseases are most often temporary and do not cause permanent turf damage, or damage that cannot be remedied with minor repairs. 
• When severe disease outbreaks occur on lawns, it may often be a result of unusual weather conditions or an underlying agronomic problem. 
• Thus, fungicide application is seldom warranted or recommended for most lawn areas.

Scout regularly for diseases to inform management decisions. 

• Although disease outbreaks are less of a concern on lawns than weeds or insects, watching for disease is an important component of a complete monitoring program. 
• The appearance of disease on a stand of turf is fundamentally dictated by interactions between three factors: temperature, amount and duration of moisture present, and the presence of an organism capable of causing disease. 
• Careful attention to these three factors, along with a working knowledge of the preferred conditions of various diseases, can be critical for avoiding significant problems. 

OBJECTIVE: Implement focused cultural practices as the primary defense against disease outbreaks on lawn turf areas.

Fertilize judiciously and lime appropriately.   

• Apply fertilizer according to current recommendations and based on a soil test. 
• Excess nitrogen will cause succulent growth that is more susceptible to disease, and some diseases are encouraged when nitrogen is deficient. 
• Adjust pH according to soil test recommendations. Disease occurrence may increase at pH extremes (too high or too low). 
• Time fertilization and liming to avoid disease critical periods (e.g. avoid fertilization in early spring and just before hot, humid weather). 

Take herbicide applications into account. 

• Herbicides can stress turfgrasses and make them more susceptible to diseases. Apply carefully according to label directions and with attention to environmental conditions. 
• Some herbicides may have fungistatic effect and provide some degree of disease control. 
• Noting fungistatic occurrences may be useful for reducing or eliminating fungicide applications. 

Irrigate with disease reduction in mind. 

• Disease-causing fungi reproduce by spores that, like seeds, need water to germinate and infect turf. Make every effort to reduce the duration of time that grass is wet from irrigation or dew. 
• Time irrigation in order to minimize duration of leaf wetness. Dry turfgrass blades reduce disease by reducing infection. 
• Water deeply and infrequently, and prevent significant moisture stress.  
• Avoid light, frequent sprinklings (syringing) except to prevent wilting in close-cut or shallow rooted turf or immediately following sod installation and during hot, dry weather. 

 
When NOT to water turf. 

Take proper mowing considerations. 

• Mowing wounds turfgrasses and can spread pathogens (disease-causing organisms). 
• Minimize wounding and shredding of grass blades by keeping blades sharp and adjusted properly. 
• Mow when turf is dry whenever possible. 
• Remove and properly dispose of clippings when diseases such as red thread and dollar spot are present at unacceptable levels. 
• Mowers should be washed and mowing order of lawns should be modified when some lawns have active disease to avoid spreading pathogens. Alternatively, a dedicated mower can be used. 
• Mowing in autumn until turf stops growing can help to reduce damage from snow molds. 

Reduce turfgrass stress. 

• Modify the landscape where needed to improve air circulation and reduce shade. 
• Reduce or eliminate traffic on areas with active disease infestation whenever possible. 
• When compaction is contributing to plant stress, take appropriate measures to relieve compaction 
• Manage excessive thatch by adjusting fertility levels or by mechanical removal. 

OBJECTIVE: Use fungicides only when sound cultural practices have not proven effective in acceptably managing a disease problem. 

Apply fungicides responsibly. 

• Obtain a laboratory confirmation of disease and a diagnostic report prior to any application, especially if you are unsure of the disease. 
• Rotate fungicides based on chemical group to discourage resistance. For ease of reference, Fungicide Resistance Action Committee (FRAC) codes are available to aid in insecticide resistance management. Refer to UMass Extension’s 2010-2011 Professional Guide for IPM in Turf for Massachusetts or http://www.frac.info. 
• Apply irrigation as necessary after fungicide applications. 
• Use preventive fungicides only in areas where diseases occurred and were documented the previous season and/or can be expected to occur in the current season. 

Collect a turf sample for laboratory diagnosis. 

• Obtain a laboratory confirmation of disease and a diagnostic report prior to any application, especially if you are unsure of the disease. 
• Collect a 4-6 inch sample from the leading edge of a problem including roots and soil to a depth of at least 2 inches and foliage showing the symptoms. 
• Keep the sample moist and cool, but do not water or seal tightly in plastic.   
• Wrap the sample in several layers of newspaper and pack it snugly in a sturdy box. 
• Take the sample before spraying a fungicide. 
• Accurate disease diagnosis requires both a representative sample and sufficient information about the cultural practices and environmental conditions, therefore a turf disease case history should be submitted with the sample.