You Are Here: Management Updates 1999 Archive September 2, 1999

Date: September 2, 1999
Category: Diseases
Subject: Gray Leaf Spot, Rust

Gray leaf spot has arrived in New England. Samples from roughs on a golf course in Woods Hole on Cape Cod have been diagnosed with gray leaf spot in the perennial ryegrass. If you have perennial ryegrass fairways, they should be protected immediately with a fungicide if you have not already done so.

We do not yet know the implications of this disease for lawns and athletic fields. Please watch for any unusually aggressive leaf spot. The disease is often misdiagnosed as drought even when the turf is being watered. The disease may also occur on tall fescue, but not other turf species. It's also the time of year for rust in many lawns. This disease is common at both ends of the management spectrum. The standard description is that the spores take 10 days to 2 weeks between infection and new spore production (rusty-colored pustules of powdery spores). If grass is slow growing because of low nitrogen, drought, compaction etc., it will not outgrow the infection and disease appears. In most cases, correction of the factors that are slowing the grass growth will eliminate the problem. In some cases, however, excess N and/or prolonged moisture (overwatering, rainy weather, poor air circulation) will also result in rust outbreaks. Rust may weaken plants but usually does not kill them. The good news is that the spores will die over the winter. Spores usually move up from southern areas which is why this disease is most common in later summer and fall.

A homeowner removed all of her rusty raspberries in an attempt to stop the rust in her lawn. Although rusts often look alike, they are caused by very different host-specific fungi- as are many of the powdery mildews. They sometimes appear at similar times because of favorable environmental conditions.

- Submitted by: Dr. Gail Schumann