Pest Alert №11 — Red Leaf Spot of Creeping Bentgrass
Recently, the diagnostic samples of greens were not exactly the usual. We are experiencing a warm stretch of weather into fall. It has been dry, except for an occasional rain shower. However, a leaf spot of creeping bentgrass can and does occur during warm periods.
Red leaf spot of creeping bentgrass is probably misdiagnosed more than it is diagnosed. Why? It is easily confused with more common foliar diseases. Dollar spot (primarily bentgrass) and anthracnose (primarily annual bluegrass) come to my mind in greens of Chicago. Also, bentgrass will turn bronze or reddish when it has physiological misgivings (shock due to cold temps and/or reaction to plant growth regulators or other abiotic stressors).
Two weeks in a row in mid to late September I saw red leaf spot in samples. The first greens looked like they had dollar spot. The look was spotty with a red infection center instead of a bleached-white infection center. The typical fungicides that work on dollar spot don’t always work on leaf spots. The second greens looked like anthracnose was the issue because the look was patchy. Those surfaces were a mix of bentgrass and Poa annua. As leaf spot develops it coalesces and can take out patches of bentgrass (aka biotypes of certain varieties).
The difficultly in diagnosing is that patience is sometimes required. The art/science required is incubation over a 24 hour period. Then you will see the resulting sporulation of cigar-shaped conidia on necrotic/infected leaf blades and stolons. Turns out I like both art and science.
