TURFGRASS DISEASE IDENTIFICATION (P4)
Yellow Tuft (Downy Mildew)
Causal Agent: Sclerophthora macrospora
Susceptible Turfgrass: All turf
Symptoms: Symptoms of yellow tuft vary depending on the grass cultivar. On cool-season turfgrass, yellow tuft causes circular patches that measure 1/4 to 4 inches in diameter. The shoots become dwarfed and turn yellow in color. Infected seedlings form individual clusters of dense shoots that are yellow in color. The tufts of shoots originate from a single node or terminal stem apex that is excessively tillered with shortened roots. Yellow tuft will mimic annual bluegrass plants in creeping bentgrass putting greens. The individual tufted plants can be easily detached from the soil surface using a knife. On St. Augustinegrass, the disease is called downy mildew and causes white streaks that are parallel to the leaf veins. The epidermis over the streaks becomes raised and turns white in color. Excessive tillering, however, does not occur in St. Augustinegrass, but plants may be stunted.
Conditions Favoring Disease: Downy mildew initially occurs in wet, poorly drained areas that are depressed. The disease typically infects cool-season turf in early to late spring and mid- to late fall. It affects St. Augustinegrass primarily during the humid weather of summer and can be more severe in shaded areas.
- Improve the soil drainage.
- Increase the air circulation.
- Use proper surface contours to minimize water movement and accumulation on the turf’s surface.
- Avoid high or excessive levels of nitrogen that result in lush growth.
Occasionally occurs in: AL, FL, GA, LA, MS, TX
Frequently occurs in: AR, CT, DE, IA, IL, IN, KS, KY, MA, MD, ME, MI, MN, MO, NC, NE, NH, NJ, NY, OH, OK, PA, RI, SC, TN, VA, VT, WI, WV.
Causal Agent: Erysiphe graminis
Susceptible Turfgrass: Kentucky bluegrass, fine-leaf fescue, bentgrass, ryegrass, and bermudagrass
Symptoms: The disease first appears on the leaves as individual tufts of fine, white mycelium. The tufts enlarge and coalesce, causing the leaves to have a grayish-white or powdery appearance. Severely infected turf turns yellow, then tan and brown in color. Stressed turf that is severely infected can die. Severely infected turf, especially in shaded areas, can become thinned.
Conditions Favoring Disease: Powdery mildew is favored by humid, cloudy weather with temperatures between 60°F and 72°F. It occurs in areas under stress, with low light, and with high humidity. Powdery mildew is also common in areas with poor air circulation, but does not require a film of water to infect turf.
- Water as needed to avoid drought stress.
- Avoid levels of nitrogen and irrigation that produce lush leaf growth.
- Raise the mower height.
- Prune tree limbs to improve air circulation and the amount of sunlight.
- Convert to a polystand of shade-adapted turfgrass.
Occasionally occurs in: AL, AR, AZ, FL, GA, KY, LA, MS, NC, NM, OK, SC, TN, TX, VA.
Frequently occurs in: CA, CO, CT, DE, OR, IA, ID, IL, IN, KS, MA, MD, ME, MI, MN, MO, ND, NE, NH, NJ, NV, NY, OH, PA, RI, SD, UT, VT, WA, WI, WV, WY.