Anthracnose of Lawns
Click for larger image Dead area of lawn killed by anthracnose with ink pen for scale

Anthracnose is usually associated with turf suffering from heat injury in midsummer, but it can also develop in spring and fall. Anthracnose may occur in conjunction with other diseases such as summer patch and Rhizoctonia brown patch. It is a common disease of bentgrass and annual bluegrass.

The most severe damage is when the anthracnose fungus (Colletotrichum) infects and colonizes the lower crown of the turfgrass plant. This is sometimes referred to as basal crown rot. Plants with a crown rot are killed, resulting in a thinning of the turfgrass stand. Spore-producing acervuli and small, black resting structures called sclerotia form on the decaying crown. The scattered structures are visible with a hand lens and appear as small pepper-like dots.

Symptoms and Diagnosis

From a distance, affected bentgrass and/or annual bluegrass appear unthrifty and have a yellow or bronze cast. Affected turf may wilt rapidly during midday and require frequent watering .

Individual plants affected with anthracnose first turn yellow and then die. Distinct leaf spots are not commonly formed by the anthracnose fungus. Instead, individual leaf blades fade from dark green to light green and then to yellow. There is no distinct region between healthy and diseased tissue as commonly observed with other leaf spotting fungi. The fungus produces conspicuous black fruiting structures called acervuli in the leaves. The acervuli are abundant in dead tissue and may also form in green, apparently healthy leaves. The black hairy or spiny fruiting bodies are easily visible with a 10X hand lens. Spines associated with ascervuli are diagnostic for Colletotrichum fungi .

Life Cycle

Anthracnose may develop throughout the growing season, although it is more common in midsummer when cool-season turf is experiencing heat or drought stress.

The anthracnose fungus, Colletotrichum graminicolum, overwinters on living plant material. Stressed turfgrass is most susceptible to infection. The fungus penetrates the root, crown and/or leaf tissue during high humidity and wet weather conditions.

Integrated Pest Management Strategies

1. Fertilizer. Get a soil test and correct fertilizer deficiencies, especially phosphorus and potassium. Very light fertilization with a balanced fertilizer during the summer may help the turf withstand stresses and recover quickly.

2. Mowing. Low frequent mowings enhance disease development. Consider raising mowing height to three inches during midsummer.

3. Watering. Use proper watering practices. Water in early morning with approximately 1 inch of water per week or to a depth of 6 inches. Avoid dry spots and frequent, light waterings.

4. Fungicides. Fungicides are continually being developed for use against fungi. Select one for your disease and read the label before applying any fungicide or pesticide. Pesticides registered for use include: azoxystrobin (Heritage), chlorothalonil (Daconil), Neem extract, copper, mancozeb, maneb, thiophanate methyl (Cleary 3336), and triadimefon.

Organic Strategies

Strategies 2 and 3 are strictly organic approaches. Organic lawn fertilizers are available and could be a viable organic approach to Strategy 1. Of the fungicides listed in Strategy 4, consult the Organic Materials Review Institute (OMRI™) for appropriate organic copper products.

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