Managing Anthracnose On Golf Course Putting Greens (P3)
Nitrogen fertility. Adequate nitrogen fertility appears to minimize anthracnose severity better than other management practices. Applying 0.1 lb N/1,000 ft2 every seven days throughout the summer months significantly reduced anthracnose severity compared to applying this rate every 28 days (Inguagiato et al., 2008). Spoon-feeding on a biweekly to monthly basis may reduce the vigor of plants based on a lack of nutrition, which would stress the plant, leaving it prone to C. cereale infection. Golf course managers may also be able to increase the amount of nitrogen in the soil by applying larger quantities of slowrelease nitrogen (0.75 to 1.5 lb N/1,000 ft2) in the fall or spring. No studies have correlated anthracnose severity with phosphorus or potassium deficiencies, but it would be important to fertilize with these nutrients based on soil test recommendations.
Mowing height. The second management practice that had a significant effect on anthracnose severity was mowing height. Many creeping bentgrass and annual bluegrass putting greens are maintained at or below 0.125 inch even under stressful environmental conditions, which greatly increases the host’s susceptibility to fungal infection. Research has shown significant decreases in anthracnose severity when mowing heights are raised by as little as 0.015 inch (0.110 to 0.125 inch or 0.125 or 0.140 inch). Golf course managers may be hesitant to increase mowing height due to potentially reducing ball speed on putting greens. However, double-cutting at the higher cutting height each day and rolling plots every other day to improve speeds will not increase disease severity at higher mowing heights (Inguagiato et al., 2009). Although no research was performed to determine the specific reason for the decrease in severity at higher mowing heights, it was hypothesized that increased leaf area would allow more photosynthesis to occur and more carbohydrates could be distributed throughout the plant to minimize stress.
Water management. Soil moisture management plays a key role in stress management and, therefore, in susceptibility of the host to infection. To alleviate plant stress by reducing temperatures within the canopy, syringe putting greens on warm (≥ 85º F), dry and sunny afternoons. If grasses were to become heat stressed late in the afternoon, C. cereale would have ample time to infect those plants prior to the turf recuperating in the evening. Areas on putting greens that are prone to drying (such as slopes) may need additional irrigation early in the morning to reduce afternoon moisture stress. Soil moisture deficits affect turf and anthracnose severity as previously discussed, but excessive water may also have a negative effect. So overwatering should be avoided. Saturated soils lead to anaerobic situations, reducing the availability of oxygen to roots and increasing plant stress.
Root cultivation. As mentioned in the introduction to this section, cultural practices that increase stress on turf will increase anthracnose severity. Therefore, aerification, deep vertical mowing (> 0.2 inch, ≥ 5 mm), topdressing and use of groomers on mowers should be avoided when the summer heat stress period has begun. Aerification should be performed in the spring and fall when the grasses are vigorously growing. Interestingly, research has shown that light vertical mowing (0.12 inch, 3 mm depth), which does not cut stolons but removes organic matter, had no effect on anthracnose severity. Even during the stressful times of year, it is still important to maintain aerobic conditions in the root zone for respiration. Spiking and hydrojecting putting greens are two possible solutions that result in minimal stress while facilitating the movement of oxygen into the root zone.