Leaf Diseases of Lawns

Pesticides updated by Joey Williamson, HGIC Horticulture Extension Agent, Clemson University, 01/13. Revised by Joey Williamson, HGIC Horticulture Extension Agent, Clemson University, 09/11. Originally prepared by Nancy Doubrava, HGIC Information Specialist, and James H. Blake, Extension Plant Pathologist, Clemson University. 06/99.

HGIC 2152

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Home lawns in South Carolina are commonly infected by leaf diseases including dollar spot, rust, gray leaf spot, powdery mildew, anthracnose and Helminthosporium leaf spot. Most of the time, these problems go unnoticed by the homeowner and do not cause significant damage to the lawn. However, when conditions are favorable for disease development, serious damage can occur. Effective control programs for most diseases must include proper cultural care of the lawn, and a basic understanding of the factors affecting disease development. For information on brown patch or large patch, see HGIC 2150, Brown Patch & Large Patch Diseases of Lawns.

Dollar Spot

Dollar spot is caused by the fungus, Sclerotinia homoeocarpa. It causes straw-colored spots about the size of a silver dollar (2 to 6 inches diameter) to appear on closely mowed turf. Grass in affected areas may die and the spots may merge to form larger, irregular patches. In coarse textured grass that is cut high, the dead spots are larger and more diffuse. Leaf blades have light tan spots with reddish-brown margins that develop across the leaves. Early in the morning you may be able to see a cobweb-like growth of the fungus over the infected area.

Dollar spot most commonly occurs on Bermudagrass, zoysiagrass, creeping bentgrass, turfgrass tall fescue and ryegrass. Dollar spot is most active from late spring through fall. The fungus develops during humid weather, when daytime temperatures are warm (59 to 86 °F) and nights are fairly cool. These conditions result in heavy dew forming on the grass.

Prevention & Treatment: Adequate fertilization will help the lawn overcome this disease. Prevent thatch buildup and remove excess thatch. Avoid drought stress by watering the lawn deeply, and thoroughly when needed, timing irrigation for early morning. Remove morning dew if possible by mowing or irrigating the lawn. Fungicide applications may be needed during moist weather in the spring and fall, when day temperatures are between 70 to 80 °F. For the home lawn, fungicides can be applied that contain azoxystrobin, thiophanate-methyl, myclobutanil, propiconazole, or triadimefon. Always apply all chemicals according to directions on the product label.

Rust

Rust fungi (Puccinia and Uromyces species) can infect most types of grasses, but occur most commonly on bluegrass, turfgrass tall fescue, ryegrass, and zoysiagrass in South Carolina. Rust diseases are favored by warm, humid conditions and develop most frequently on lawns that are stressed by drought, low nitrogen, and shade. Disease first appears on leaves as tiny orange to reddish-brown flecks that enlarge to form raised pustules. Lawns that are heavily infected become thin and weak with an orange or reddish color.

Prevention & Treatment: Rust is most often a problem on lawns with too much shade. Avoid stressing the lawn. Maintain adequate nitrogen levels and irrigate during drought conditions. Mow the grass regularly, and remove clippings, being sure not to cut the lawn too low. Do not overwater. Fungicides are usually not necessary in actively growing lawns. If necessary, home lawn fungicides containing propiconazole, triadimefon or azoxystrobin will aid in rust control.

Gray Leaf Spot

Gray leaf spot is caused by the fungus, Pyricularia grisea, and causes severe damage primarily on St. Augustinegrass (a. k. a. "Charlestongrass") and ryegrass. Turfgrass tall fescue may also be damaged by gray leaf spot. Leaf spots on grass blades are tan to gray with purple to brown margins. When the disease is severe, the entire planting may appear a brownish color or scorched, similar to damage caused by drought. This disease most commonly occurs during warm, rainy periods in the summer.

Prevention & Treatment: Plant resistant cultivars. Avoid excessive applications of nitrogen, especially during warm, humid weather. Irrigate deeply only when needed and in the early morning. Avoid stresses induced by herbicides, drought, or compacted soil. Improve air movement and light intensity, by pruning trees and undergrowth. If chemical control is necessary, the most effective fungicides containing azoxystrobin or thiophanate-methyl are available for use in the home lawn. Less effective alternative fungicides contain propiconazole or triadimefon. Always apply all chemicals according to directions on the product label. For more information, see HGIC 2151, Gray Leaf Spot on St. Augustinegrass.

Powdery Mildew

This disease is caused by the fungus, Blumeria graminis, and appears as a grayish-white powdery growth on the surfaces of the grass blades. Leaves may turn yellow and gradually die. It is an important disease on bluegrass, turfgrass tall fescue and bermudagrass, especially in areas of shade or little air movement.

Prevention & Treatment: Increase sunlight penetration to densely shaded areas, or select a more shade tolerant cultivar. A balanced fertilization program is important for the lawn. Mow the lawn often and at the recommended height. Increasing air circulation will also help to control powdery mildew. Fungicides containing myclobutanil, propiconazole or triadimefon can be used on the home lawn in areas where environmental conditions cannot be modified. Always apply all chemicals according to directions on the product label

Anthracnose

This leaf disease causes the most severe damage on creeping bentgrass and annual bluegrass and is caused by the fungus, Colletotrichum cereale. It occurs during the peak of hot weather when cool-season grasses are barely growing. It also infects centipedegrass during very rainy periods in the spring and summertime. In creeping bentgrass, anthracnose causes a stem rot at the base of the plant, which can cause the lawn to turn yellow and die.

Prevention & Treatment: Maintain the lawn in as healthy a condition as possible with a balanced fertilization program. Reduce thatch and soil compaction. Chemical control is generally not needed on centipedegrass due to its quick recuperative potential. Fungicides containing azoxystrobin, thiophanate-methyl, propiconazole, or myclobutanil are available for control, when other measures fail. Always apply all chemicals according to product label directions.

Helminthosporium Diseases

The diseases in this group are commonly referred to as melting out, leaf spot, net-blotch, and crown and root rot. These diseases are caused by the fungi Bipolaris and Drechslera species, but were previously classified as Helminthosporium species.

Bipolaris and Drechslera species cause leaf spotting and melting out disease primarily on bluegrass and bermudagrass, but turfgrass tall fescue, creeping bentgrass, ryegrass, and zoysiagrass are also affected by this complex of diseases. In turfgrass tall fescue, bermudagrass and ryegrass the disease is most active during cool, wet weather in the spring and fall. However, in bluegrass and creeping bentgrass, the disease is most active during warm, wet weather in late spring, summer and early fall. The diseases generally start as leaf spots and may progress to sheath and crown rots. Leaves have circular to elongate, purple or brown spots with straw-colored centers. When disease lesions become extensive, turfgrass leaves turn reddish-brown, then yellow and die. Melting out may follow, and appears as a reddish-brown rotting of the leaf sheaths, crowns, rhizomes and stolons. Centipedegrass is rarely affected adversely by these fungi.

Prevention & Treatment: Avoid high nitrogen fertilization and watering practices that provide long periods of wet or humid conditions. Frequent mowing at proper heights will provide better drying conditions in the turf and help to reduce the leaf spot phases of these diseases. Provide adequate water with infrequent but deep irrigation to help avoid crown and root rot phases. Reduce excessive thatch during May for warm-season turfgrasses. Submit a soil sample to test for soil nutrients, and maintain a sufficient soil potassium level.

Fungicides for control of Helminthosporium diseases include azoxystrobin and propiconazole, with azoxystrobin the most effective. Apply all chemicals according to directions on the product label.

Excerpted from Diseases of Turfgrasses in the Southeast, Martin, B., EB 146, 1994.

Table 1. Fungicides for Control of Brown Patch & Large Patch on Home Lawns
Fungicides Examples of Brands Form of Product Available
1Resistance to the fungicide by the leaf disease fungi will develop from continued exclusive use of either azoxystrobin or thiophanate methyl. Always alternate either of these fungicides with one of the others. Follow directions on product label for use. In general, azoxystrobin will control most turfgrass diseases for 28 days. The other four fungicides will control the diseases for 14 days. Irrigate according to label directions after application of granular products.
2RTS = Ready to Spray (a hose-end sprayer)
Landscape professionals should consult the 2012 Pest Control Guidelines for Professional Turfgrass Managers for recommendations.
Azoxystrobin1 Heritage G
Maxide Dual Action Disease Killer
    (discontinued, but may be purchased on internet)
Granules 0.31%
Granules 0.31%
Myclobutanil Spectracide Immunox Lawn Disease Control
Spectracide Immunox Lawn Disease Control
Ferti-lome F-Stop Lawn Fungicide
Lebanon Eagle 0.62G Specialty Fungicide
Granules 0.39%
RTS2 2.00%
Granules 0.39%
Granules 0.62%
Propiconazole Ferti-lome Liquid Systemic Fungicide II
Bonide Infuse Systemic Disease Control RTS2
Bayer Advanced Fungus Control for Lawns
RTS2 1.55%
RTS2 1.55%
Granules 0.51%
& RTS2 2.42%
Thiophanate methyl1 Scotts Lawn Fungus Control
Lesco T-Storm 2G Systemic Fungicide for Turf &
    Ornamentals
Bonide Infuse Systemic Disease Control Granules
    (NOT the same active ingredient as in Bonide Infuse RTS2)
Granules 2.30%
Granules 2.08%

Granules 2.08%
Triadimefon Lebanon Turf Fungicide contains 1% Bayleton Granules 1.00%

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This information is supplied with the understanding that no discrimination is intended and no endorsement of brand names or registered trademarks by the Clemson University Cooperative Extension Service is implied, nor is any discrimination intended by the exclusion of products or manufacturers not named. All recommendations are for South Carolina conditions and may not apply to other areas. Use pesticides only according to the directions on the label. All recommendations for pesticide use are for South Carolina only and were legal at the time of publication, but the status of registration and use patterns are subject to change by action of state and federal regulatory agencies. Follow all directions, precautions and restrictions that are listed.