Alfredo Martinez-Espinoza

Source(s): Alfredo Martinez-Espinoza

Susceptible Turfgrass

St. Augustine grass is most commonly attacked by gray leaf spot but it also attacks perennial ryegrass, Bermuda grass, centipede grass, bent grass and various species of fescue. Gray leaf spot is especially severe on new St. Augustine lawns.

Symptoms

The symptoms of gray leaf spot vary depending on the grass cultivar. On St. Augustine grass, gray leaf spot first appears as small, brown spots on the leaves and stems. The spots quickly enlarge to approximately ¼ inch in length and become bluish-gray in color and oval or elongated in shape. Mature lesions are tan to gray in color and have depressed centers with irregular margins that are purple to brown in color. A yellow border on the lesions can also occur. In cool-season turf grass, the symptoms are similar to those of melting-out.

Conditions Favoring Disease

Gray leaf spot is favored by daytime temperatures between 80ºF to 90ºF and night temperatures above 65ºF. It is also found in areas with high nitrogen levels and that are stressed by various factors, including drought and soil compaction. This disease is most severe during extended hot, rainy and humid periods.

Management of Gray Leaf Spot

• Avoid medium to high nitrogen levels during mid-summer. Use fertilizers with slow-release nitrogen sources.
• Irrigate turf deeply and as infrequently as possible to avoid water stress.
• Allow water to remain on leaves for only a short period of time. Water from 10 pm to 10 am.
• Reduce thatch by vertical cutting.
• When possible, plant turf grass that is resistant to gray leaf spot.
• Avoid using herbicides or plant growth regulators when the disease is active.
• Fungicides are available to control the disease. Consult the current Georgia Pest Management Handbook.

Resource(s):

• Turfgrass Diseases in Georgia
• Guide to Turfgrass Fungicides
• Turfgrass Diseases: Quick Reference Guide

Source(s):

• Alfredo Martinez
• Lee Burpee

Large patch disease of turfgrass is most common in the fall and in the spring as warm season grasses are entering or leaving dormancy. Large patch is caused by the fungus Rhizoctonia solani. It can affect zoysiagrass, centipedegrass, St. Augustinegrass and occasionally bermudagrass.

Symptoms of this lawn disease include irregularly-shaped weak or dead patches that are from 2 feet to up to 10 feet in diameter. Inside the patch, you can easily see brown sunken areas. On the edge of the patch, a bright yellow to orange halo is frequently associated with recently affected leaves and crowns. The fungus attacks the leaf sheaths near the thatch layer of the turfgrass.

Large patch disease is favored by:

• Thick thatch;
• Excess soil moisture and poor drainage;
• Too much shade which stresses turfgrass and increases moisture on turfgrass leaves and soil;
• Early spring and late fall fertilization.

If large patch was diagnosed earlier, fall is the time to control it. Applying azoxystrobin (Heritage), flutolanil (Prostar), metconazole (Tourney), myclobutanil (Eagle), polyoxin (Endorse), , propiconazole (i.e. Banner Maxx), pyraclostrobin (Insignia), thiophanate methyl (3336 F, G and Plus), or triadimefon (Bayleton), at curatives rates in late September or early October and repeating the application 28 days later are effective for control of large patch during fall. Fall applications may make treating in the spring unnecessary. Always follow label instructions, recommendations, restrictions and proper handling.

Cultural practices are very important in control. Without improving cultural practices, you may not achieve long term control.

• Use low to moderate amounts of nitrogen, moderate amounts of phosphorous and moderate to high amounts of potash. Avoid applying nitrogen when the disease is active.
• Avoid applying N fertilizer before May in Georgia. Early nitrogen applications (March-April) can encourage large patch.
• Water timely and deeply (after midnight and before 10 AM). Avoid frequent light irrigation. Allow time during the day for the turf to dry before watering again.
• Prune, thin or remove shrub and tree barriers that contribute to shade and poor air circulation. These can contribute to disease.
• Reduce thatch if it is more than 1 inch thick.
• Increase the height of cut.
• Improve the soil drainage of the turf.
• Apply lime if soil pH is less than 6.5 (Except on centipede lawns).

See the current Georgia Pest Management Handbook for more information. Check fungicide labels for specific instructions, restrictions, special rates, recommendations and proper follow up and handling.

Resource(s):

• Turfgrass Diseases
• Turfgrass Diseases: Quick Reference Guide
• Common Landscape Diseases in Georgia

Center Publication Number: 271

Source(s):

• Lee Burpee, Plant Pathology Department, The University of Georgia.
• Alfredo Martinez-Espinoza, The University of Georgia.

“Large Patch” and “Spring Dead Spot” appear on turfgrass during spring green-up. While symptoms appear in the spring, truly effective disease management starts in the fall.

Large Patch

Rhizoctonia large patch is likely to develop on zoysia, centipede and St. Augustinegrass during cool, wet periods in spring. Zoysia is particularly affected. Look for yellow or straw-colored patches a few inches to 10 feet or more in diameter. Turfgrass shoots at perimeters of patches will have leaf sheaths that are dark brown to black. Lush, fertile turf is highly susceptible to Rhizoctonia; therefore, delay nitrogen applications until mid-May or later. Sound cultural practices help control the disease; therefore avoid frequent light irrigation to reduce humidity. Allow time during the day for plant canopy to dry. Increase air circulation. Shrub and tree barriers contribute to shade and lack of air circulation. Reduce thatch (no more than 1 inch thick).

Fungicides can be applied in the spring to aid in the control of the disease. Fungicides that contain azoxystrobin, flutolanil, and pyraclostrobin, have provided 28 days control of large patch in tests at UGA. Repeat applications may be required if night temperatures less than 55oF persist after the grasses come out of dormancy. However the most effective management of large patch occurs in the fall.

Spring Dead Spot

Spring dead spot is typically more damaging on intensively managed turfgrass (such as bermudagrass greens) compared to low maintenance areas. Initial symptoms appear in the spring, when turf resumes growth from its normal winter dormancy. As the turf ‘greens-up,’ circular patches of turf appear to remain dormant, roots, rhizomes and stolons are sparse and dark-colored (necrotic). No growth is observed within the patches.

Recovery from the disease is very slow. The turf in affected patches is often dead, therefore recovery occurs by spread of stolons inward into the patch. The disease is caused by several fungi in the genus Ophiosphaerella (O. korrae, O. herpotricha and O. narmari). These fungi infect roots in the fall, predisposing the turf to winter kill. Research shows that freezing temperatures make the disease worse.

Spring treatment consists of encouraging growth so that the stolons will move into the dead area. Implement regular schedules of dethatching and aerification. These activities encourage growth and will help to control the disease.

Fall application of fungicides is essential for an effective control. Currently, fenarimol, myclobutanil, azoxystrobin, thiophanate-methyl, and propiconazole are labeled for spring dead spot control. Management strategies that increase bermudagrass cold tolerance such as applications of potassium in the fall prior to dormancy are thought to aid in disease management. However, researchers have recently found that fall applications of potassium at high rates actually increased spring dead spot incidence. Therefore, application of excessive amounts of potassium or other nutrients, beyond what is required for optimal bermudagrass growth, is not recommended.

Resource(s):

• Turfgrass Diseases
• Turfgrass Diseases: Quick Reference Guide
• Common Landscape Diseases in Georgia