Anthracnose Foliar Blight and Basal Rot
Acervuli of Colletotrichum cereale on annual
Anthracnose can occur both as a foliar blight and a rot of the crown, stem base, and roots (basal rot). Anthracnose foliar blight typically occurs during mid-summer and attacks the leaves and stems of most cool-season turfgrass species. Particularly severe cases can develop on annual bluegrass fairways on golf courses. Anthracnose basal rot can occur during spring, summer, and fall and develops in the crowns, stem bases, and roots of annual bluegrass and creeping bentgrass, usually on golf course putting greens.
Symptoms and signs
Anthracnose foliar blight appears as irregular yellow or bronze patches of diseased turf. Symptoms on individual plants first appear as yellow or red lesions on the oldest (outermost) leaves, then progress to a blighting of younger leaves and shoots. Occasionally, fungal fruiting structures called acervuli can be observed with a good quality hand lens on diseased leaves and stems. Acervuli resemble small, black pin cushions and are the site of spore production.
Anthracnose basal rot symptoms on annual bluegrass putting green.
Rot of stem bases and crowns on annual bluegrass affected by anthracnose basal rot.
Anthracnose basal rot symptoms vary depending on the grass species affected. On annual bluegrass, symptoms appear as a bright yellowing of the turf in irregular patches. Affected bentgrass turf typically appears as irregular red or bronze patches and rarely appears yellow. On individual plants affected with anthracnose basal rot, a dark brown or black color is present at the base of the plant. As the disease worsens, the darkening (rotting) progresses up the stem and acervuli can be observed with a hand lens on stem and leaf tissue.
The causal fungus, Colletotrichum cereale, survives the winter as dormant resting structures called sclerotia and as dormant mycelium in infected plant debris. During early spring outbreaks of anthracnose basal rot, the fungus, which may have overwintered in the plant, initiates infection at the base of the plant. Outbreaks of anthracnose foliar blight and/or basal rot can result when spores produced in acervuli are dispersed by splashing water or tracked by mowing equipment from one area to another. These spores then germinate and cause new infections on other plants. Anthracnose is likely to occur when plants are growing slowly (during periods of hot and cold temperatures), during overcast periods, and in high humidity conditions.
Proper fertilization and maintaining good soil physical conditions are the most effective cultural approaches to managing anthracnose. If your turf is underfertilized, increase the rate and/or frequency of nitrogen fertilizer applications. This will improve resistance to the disease and aid in turf recovery. Add potassium and phosphorus if your soil test report indicates a need. Improved drainage and a regular core aeration program will reduce excess soil moisture, alleviate compaction, and improve root growth, creating conditions that are less favorable for anthracnose.
On golf courses in Pennsylvania and other northeastern states, annual bluegrass is very susceptible to anthracnose, while creeping bentgrass is usually quite resistant. Any management practice that encourages creeping bentgrass populations over annual bluegrass will aid in reducing severity of this disease.
Fungicides are only used to control anthracnose on golf courses. Preventative (before the disease occurs) applications of fungicides are generally more effective in controlling anthracnose foliar blight and basal rot than curative (after the disease appears) applications. Application timing will vary from one region to another and possibly from year to year at the same location. The best way to time your applications is to keep records for several seasons of the environmental conditions under which the disease occurred on your course, then apply fungicides when conditions are conducive for disease development.