Anthracnose is a persistent and destructive foliar disease that affects a wide range of turfgrass species, thriving in the cool, wet conditions common during spring and fall. Caused by the fungus Colletotrichum cereale, this pathogen targets the crown, leaves, and stems of grass, disrupting the plant's ability to photosynthesize and store energy. Homeowners, groundskeepers, and turf managers frequently observe irregular patches of thinning, discolored grass where the vibrant green of a healthy lawn has been replaced by a sickly yellow or tan appearance.
Understanding the Foe: The Biology of Colletotrichum cereale
The severity of anthracnose is directly tied to environmental conditions that favor the fungus over the grass. The pathogen survives the winter within infected plant debris, soil, and even on mowing equipment, waiting for the right moment to strike. Extended periods of leaf wetness, temperatures between 50°F and 90°F, and high humidity create the perfect storm for infection. Unlike some diseases that prefer extreme heat or cold, anthracnose is notorious for flaring up during the transitional seasons when the weather is unpredictable and moisture is abundant.
Visual Identification: Symptoms on the Lawn
Recognizing anthracnose early is critical for implementing an effective response, as the symptoms can vary depending on the type of grass and the stage of the disease. On closely mown turf, the disease often presents as small, water-soaked spots that rapidly expand into dark, sunken lesions. These lesions often have a characteristic "frog-eye" or ring appearance, where the center of the patch may appear tan while a darker border surrounds it. In taller fescue or ryegrass, you might notice dark, slimy streaks along the grass blades near the soil line, a sign of the pathogen attacking the crown.
Distinguishing from Other Stress Factors
Because anthracnose symptoms closely resemble those caused by drought stress or general summer decline, misdiagnosis is common. A key differentiator is the pattern of the damage; drought stress usually appears uniformly across the lawn during a heatwave, whereas anthracnose develops in irregular patches following cool, rainy weather. Furthermore, pulling back the affected grass often reveals a dark, rotted crown at the base of the stem, a clear indicator of fungal rot rather than simple dehydration.
Cultural Practices: The First Line of Defense
Long-term management of anthracnose relies heavily on cultural practices that reduce humidity and improve the overall vigor of the turf. Since the fungus thrives in moisture, ensuring proper air circulation and rapid drying of the leaf surface is paramount. This involves mowing high enough to encourage deep rooting, avoiding evening watering, and designing landscapes to promote airflow. Core aeration in the fall or spring alleviates soil compaction, allowing water to penetrate deeply rather than sitting on the surface and creating a hospitable environment for the fungus.
Implement a deep and infrequent watering schedule to encourage roots to grow downward.
Mow regularly, never removing more than one-third of the leaf blade at a time.
Sharpen mower blades frequently to prevent tearing the grass, which can create entry points for the disease.
Remove excess thatch through dethatching or vertical mowing to reduce humidity around the crown.
Chemical Control and Resistance Management
When cultural methods are insufficient, chemical intervention becomes necessary to protect the turf. Fungicides containing active ingredients such as azoxystrobin, propiconazole, or chlorothalonil are effective against anthracnose, but timing is everything. Applications should be made at the first sign of symptoms and repeated according to the label instructions, usually every 14 to 21 days during favorable weather. To prevent the pathogen from developing resistance, it is advisable to rotate between different chemical classes rather than relying on a single product season after season.
