Anthracnose is a fungal foliar disease that affects both cool-season and warm-season turfgrass species globally. The cool-season turfgrass species, particularly Poa annua and Agrostis stolonifera on putting greens in transition zones or subtropical environments, are most susceptible to anthracnose caused by Colletotrichum cereale. Other cool-season turfgrass hosts include Festuca, Lolium, and additional Poa species. Anthracnose also occurs on warm-season turfgrasses like Axonopus, Cynodon, Eremochloa, Paspalum, and Zoysia species, although it is generally less damaging than on cool-season turfgrasses and is caused by different Colletotrichum species. Anthracnose is characterized by the production of asexual spores in acervuli.
Credit: PACE Turf
Causal agents
The causal agent of anthracnose in cool-season turfgrasses is C. cereale. Additionally, two other fungi, Microdochium bolleyi and Lectera colletotrichoides, have been associated with anthracnose symptoms in turfgrass, but their significance as pathogens is not fully understood.
Primary Hosts
In cool, humid climates, anthracnose is particularly damaging in Poa annua. Agrostis stolonifere is most susceptible when grown on putting greens in the transition zone or subtropical environments.
Disease Cycle
The causal agent of anthracnose, C. cereale, survives in unfavorable periods as mycelium in decaying plant debris or living host tissue. When turfgrass plants are under stress, the fungus can penetrate foliage, stem, or root tissues. Infection occurs when atmospheric humidity is high and leaves are wet. Acervuli, which are fungal fruiting structures, form on blighted or necrotic tissue. Conidia, the asexual spores of the fungus, are then disseminated to uninfected plants through wind, water, foot traffic, or equipment. Conidia germinate within 2-6 hours and initiate infection in the host tissue.
Epidemiology
Anthracnose, a fungal disease, thrives in high humidity, overcast weather, and excessive moisture in the leaf canopy. Weakened plants due to factors like low mowing height, low fertility, drought stress, and extreme temperatures are more vulnerable. Phosphorus, potassium, and nitrogen deficiencies increase susceptibility. Anthracnose affects Poa annua year-round, with foliar blight in summer and spring outbreaks of basal rot. Deep vertical cutting may aid invasiveness in C. cereale, but other cultivation practices do not worsen the disease. Anthracnose is common in Agrostis stolonifera putting greens in transition zone and subtropical climates, with prevalent basal rot and foliar blight under specific weather conditions.
Symptoms
Symptoms of anthracnose foliar blight include yellow or reddish brown leaf discoloration, loss of shoot density, and oblong, reddish brown leaf lesions. Acervuli with black setae are visible on affected tissues. Anthracnose basal rot causes yellowing and death of patches or scattered plants. Infected tillers turn yellowish orange, while green tillers may remain. Crown tissues exhibit water-soaked or black rot, leading to patches changing from orange to reddish brown, then yellow and dying. Thinning or complete die-off of large areas resembling brown circular patches may occur. Advanced stages show black fungal mycelium, hyphopodia, infection mats, and acervuli on infected stolons or stem bases.
Credit: John Kaminski/Penn State University
Signs
Signs of anthracnose include the presence of acervuli, which are small, dark, elongated structures within infected tissues. These acervuli often have setae, which are long, dark brown or black, septate spines protruding from them. Another sign is the presence of appressoria and hyphopodia, which are small, dome-shaped structures found on exposed stem bases or stolons. In advanced stages, black aggregates of fungal mycelium, hyphopodia, infection mats, and acervuli may be present on infected stolons or stem bases. Crescent shaped conidia, asexual spores, can be found in abundance within acervuli. These spores are single-celled and generally have an oil-like droplet in its center.
Credit: John Kaminski/Penn State University
Management
Effective management of anthracnose in turfgrass requires a combination of cultural and chemical strategies. Cultural practices focus on creating optimal growing conditions, proper fertility management, irrigation practices, mowing techniques, and overall turf health. These practices help minimize disease severity and promote turf recovery. Chemical control involves the use of fungicides to prevent and manage anthracnose outbreaks. However, it is important to use fungicides judiciously, considering the risk of fungicide resistance and incorporating best-management practices to reduce the reliance on chemical treatments. By implementing both cultural and chemical approaches, turfgrass managers can effectively control and mitigate the impact of anthracnose on their turf.
Cultural
Effective cultural practices play a crucial role in managing anthracnose. It is important to provide proper fertility to the turf by avoiding nutrient deficiencies, particularly nitrogen, phosphorus, and potassium. Nitrogen should be applied in moderation and at low rates during periods of drought or high-temperature stress. Maintaining a foliar nitrogen concentration of 3.4% (dry weight) is considered critical for disease suppression on putting greens. Adequate potassium levels in the soil (above 50 ppm) and clipping tissue (above 2% potassium) are also necessary to minimize disease symptoms.
Avoiding drought stress by providing sufficient irrigation and avoiding excessively wet conditions is important. Irrigating to 80% of evapotranspiration is considered ideal. Light, frequent applications of topdressing sand throughout the growing season to bury the crown of the plant can help reduce disease symptoms and promote turf recovery. Routine cultivation practices such as aerification and topdressing are beneficial to minimize thatch accumulation and maintain soil drainage. Proper mowing height, increased during periods of summer stress, and reducing mowing frequency are recommended. If green speed is a concern, raising heights, but increasing mowing frequency is the best option. Additionally, improving overall turf health by removing trees, installing fans, or selecting turfgrass species with better resistance can help reduce anthracnose development.
Chemical
Controlling anthracnose in turfgrass requires a careful and strategic approach with chemicals. In preventive applications, tank-mixes of a DMI fungicide and chlorothalonil, at two-week intervals, have proven to be effective on creeping bentgrass/annual bluegrass greens. However, it’s essential to avoid high rates of DMI fungicides during the summer to prevent undesirable growth-regulator effects. For anthracnose control using DMI fungicides alone, apply in 5 gallons of water per 1,000 square feet, while other fungicides require a minimum spray volume of 2 gallons per 1,000 square feet with excellent one-pass coverage using appropriate nozzles.
Tank-mixes of fosetyl-Al + iprodione or chlorothalonil have also shown good results in controlling anthracnose preventively. Curative applications should include chlorothalonil tank-mixed with a systemic for best results, avoiding the use of chlorothalonil alone. Be cautious with flutolanil and pre-emergent herbicides dithiopyr (Dimension) and bensulide (Betasan) as they can enhance damage from anthracnose. Repeated application of iprodione and vinclozolin alone can also worsen the situation.
Trinexapac-ethyl (Primo) at high rates and short intervals has not increased anthracnose severity and may even reduce it by improving turf tolerance to low mowing and enhancing plant health. Similarly, mefluidide (Embark) or ethephon (Proxy) + trinexapac ethyl applied in the spring to suppress annual bluegrass seedheads will not increase anthracnose severity and may lead to a reduction in severity.
Azoxystrobin and other QoI fungicides performed well in early research trials, but the emergence of resistant strains is now a concern. Thus, relying on these fungicides for anthracnose control is not recommended. Instead, consider using chlorothalonil, fosetyl-Al, fludioxonil, DMIs, penthiopyrad, and polyoxin-D, mineral oil (Civitas), and PCNB. Remember, these materials are best used preventively and may cause phytotoxicity during hot weather or severe environmental stress.
Resistance has been identified to the following chemical classes: QoIs, DMIs, and benzimidazoles.