IPM Identification and Mangement Of Turfgrass Diseases

Author(s)

Anthroacnose basal rot

Pathogen: Colletotrichum cereale
Hosts: creeping bentgrass, annual bluegrass

Symptoms and signs

From a distance, infected annual bluegrass appears unthrifty and has a yellow or bronze cast (Figure 2). Infected bentgrass first appears purple to reddish brown, resembling a dry spot (Figure 3). The symptoms on the green often appear as a patch, because the fungus differentially infects annual bluegrass or susceptible selections (clones) of creeping bentgrass on the putting surface. Bentgrass within the affected patches is thinned.

Colletotrichum cereale produces acervuli (fruiting structures) on leaves, stems and crowns (Figure 4). Acervuli are surrounded by sterile setae (black, hairlike structures) (Figure 4, inset A). Setae are easily visible with a 20X hand lens, so turfgrass managers and other turfgrass professionals often use the observation of setae to diagnose the disease. To determine if the disease is active, however, it is necessary to examine the acervuli for viable conidia (spores), which are produced in a gelatinous matrix on the surface of the acervuli. The conidia are single celled and crescent shaped and can only be seen under high magnification (Figure 4, inset B). This usually requires the assistance of a turfgrass pathologist. Another indication that the disease is active is the observation of sporulation in green tissue (Figure 5).
Conidia germinate to form darkly pigmented appressoria (infection structures). The presence of appressoria under the leaf sheaths on green tissue is another indication that the disease is active. Appressoria are abundant on lower leaf sheaths and appear through a hand lens as small pepperlike dots (Figure 6). A close-up reveals the germ pore (Figure 7) through which C. cereale penetrates host tissue.
Crowns, old stems and roots of bentgrass or annual bluegrass appear black due to the presence of mycelial mats (aggregate hyphae) and other fungal structures in this tissue (Figure 8).

Conditions

Anthracnose basal rot most often develops during the warm, humid weather of midsummer, but it may occasionally occur during cool weather. Disease development is usually associated with predisposing factors such as high temperature and humidity, excessive soil moisture, low mowing heights and soil compaction, all of which stress the turfgrass. The disease also tends to be more severe in situations where the greens have been allowed to dry out. The fungus has been observed to overwinter in crowns and roots. Infected but symptomless plants may survive until they are exposed to stress conditions.

The information herein is supplied with the understanding that no discrimination is intended and that listing of commercial products, necessary to this guide, implies no endorsement by the authors or the Extension Services of Nebraska, Colorado, Wyoming or Montana. Criticism of products or equipment not listed is neither implied nor intended. Due to constantly changing labels, laws and regulations, the Extension Services can assume no liability for the suggested use of chemicals contained herein. Pesticides must be applied legally complying with all label directions and precautions on the pesticide container and any supplemental labeling and rules of state and federal pesticide regulatory agencies. State rules and regulations and special pesticide use allowances may vary from state to state: contact your State Department of Agriculture for the rules, regulations and allowances applicable in your state and locality.