Symptoms

Anthracnose is associated with decline of both annual bluegrass and creeping bentgrass on putting greens. It occasionally is found on senescing leaves of Kentucky bluegrass and tall fescue during periods of heat or moisture stress, but is not considered a serious problem on these turfgrass species.

Anthracnose may occur throughout the growing season but is most common in midsummer during periods of high air and soil temperatures. From a distance, affected bentgrass and/or annual bluegrass appears unthrifty and has a yellow or bronze cast (Figures 1 and 2). Affected turf wilts rapidly during midday and requires frequent irrigation. The disease may have an uneven distribution as it differentially attacks clumps of annual bluegrass or susceptible selections (clones) of creeping bentgrass on the putting surface.

Figure 1. Anthracnose of annual
bluegrass on a putting green

Figure 2.  Anthracnose of creeping
bentgrass on a putting green

Individual plants affected with anthracnose first turn yellow and then die. Distinct leaf spots are not formed. Instead, individual leaf blades fade from dark to light green and then yellow. There is no distinct margin between healthy and diseased tissue as is commonly observed with other leaf spotting fungi. The fungus produces conspicuous black fruiting structures called acervuli with spiny hairlike structures called setae on leaves and crowns that are easily visible with a 10X hand lens (Figure 3). Acervuli are abundant on dead tissue but may also form on green, apparently healthy leaves.

Figure 3.  Fruiting bodies (acervuli)
of anthracnose fungus on lower leaf
sheaths. Note the spiny black
projections called setae

Figure 4.  Mycelial mats form in the
basal crown region of infected
creeping bentgrass

Figure 5.  Microscopic view of
acervulis with setae and
spores (conidia)

Conditions

Anthracnose most often develops during the warm, humid weather of mid-summer but it may occasionally occur during cool weather. Details on the disease cycle remain sketchy, but the disease is usually associated with predisposing factors such as high temperature and humidity, excessive soil moisture, low mowing heights and compaction. Recent research suggests the fungus may infect the lower leaf sheaths and crowns and remain latent for several weeks. Infected but symptomless plants may survive until they are exposed to temperature or moisture extremes.

Control Anthracnose is one of the more difficult diseases to control, especially after symptoms appear. The best strategy is to prevent the occurrence of the disease. Several cultural practices may help. Turfgrass grown at optimal nutritional levels is less likely to be damaged. Therefore maintain a balanced fertilization program. Do not starve the turf, especially of nitrogen, during the summer months. Light fertilizations with a balanced fertilizer during the summer may help the turf withstand stresses and recover quickly from anthracnose damage.

Low, frequent mowing may enhance anthracnose development. Recent studies indicate that raising the mowing height, even to 5/32 inch, can help reduce turfgrass stress, which in turn may decrease anthracnose severity. Use walk-behind mowers on greens with a history of the disease and avoid double cutting or mowing in two directions. Also mow the perimeter of the green (the so-called clean-up lap) every other day to prevent compaction. Don't mow when the greens are wet if anthracnose is present.

Anthracnose tends to be more severe on putting greens with poor air movement and poor rooting mix drainage. On greens with a history of the disease, consider a rigorous aerification program in fall and spring. Deep tine or core aerify in the fall. Compacted greens may be periodically aerated by spiking, slitting, or hydro-jecting, but avoid excessive amount of injury to the turf during periods of stress. Do not topdress during periods of turfgrass stress. Don't overwater putting greens either by irrigation or supplemental watering by hand (syringing). Excessive soil moisture may damage roots and decrease photosynthesis. This puts the grass into a tail spin and predisposes it to anthracnose injury.

Several fungicides (see table) are labeled for anthracnose control. All products work best when applied on a preventive or early curative schedule. Applications after development of severe damage to putting greens are not very effective. Furthermore, some strains of C. graminicola may be insensitive (resistant) to benzimidazole (thiophanate methyl) and QoI (azoxystrobin, trifloxystrobin) fungicides. Preventive applications of reduced rate tank mixes of a DMI fungicide (e.g. triadimefon, propiconazole) and chlorothalonil at two-week intervals have provided good control of anthracnose in studies conducted in Kentucky. During an anthracnose outbreak, avoid excessive fungicide applications. Superintendents may try multiple products at frequent intervals in the hopes of reversing damage from anthracnose. In most cases, these attempts fail. The most rapid improvement from anthracnose damage occurs following significant (cooler) weather changes.

fair-good

7-14

Daconil
Thalonil
Manicure

QoI

fair-good
possible resistance problems

21-28

Heritage

DMI

fair-good

14-21

Rubigan

DMI

fair-good

14-21

Eagle

DMI

fair-good

14-21

Banner MAXX

Benzimidazole

fair-good
possible resistance problems

10-14

Cleary's 3336
Fungo
Cavalier

DMI

fair-good

14-28

Bayleton
Proturf Fungicide VII

QoI

fair-good

14-21

Compass

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