Fall typically brings cooler and wetter conditions, although you wouldn’t know it if you looked at the drought monitor. However, the Central and Great Lakes regions are seeing a bit more much needed rain this year.
With these meteorological patterns come different disease pressures. Incidence of yellowish, off-color patches is more common this time of the year. It could be on a home lawn, sports fields, or even golf course roughs.
Turfgrass rust is a common problem on ryegrasses and bluegrasses. Less often, it may show up on Bermuda grass, zoysiagrass, and tall fescue. It is commonly called leaf rust, crown rust, and stem rust, but it's largely just a cosmetic issue.
It is a really good indicator, however, of grasses that are slower growing due to water or nitrogen deficiencies. While the infected areas may not become apparent to everyone immediately, the tell-tale orangish to brown dusty staining on shoes and mowers should be sufficient evidence that disease activity is ongoing.
The disease is caused by a variety of fungi, most often a Puccinia or Uromyces species. Upon closer inspection, early infections appear as small, yellow spots on the leaf and as it progresses, will enlarge and eventually the fungus will break through the outer surface of the leaf. These spots become pustules which will burst when disturbed, releasing spores, and in larger amounts will leave the above-mentioned dust on anything that has traversed the infected areas.
Rust fungi overwinter in living plant tissue awaiting the proper weather conditions and plant stress factors for prime development time. Optimum development conditions include prolonged leaf wetness and at least 10 hours of air temperatures in the 68 F to 86 F range.
Other factors that are involved in disease progression include drought stress, low mowing height, and excessive shade. In extreme cases, rust can thin a stand of turf and potentially cause plant mortality. Rust infected stands can also allow more weed invasion and can lead to winter loss.
There are several steps involved in cultural management, and it starts with selecting resistant varieties of turfgrass seed. NTEP has data regarding improved varieties specifically bluegrasses and ryegrasses.
Other practices include maintaining irrigation as needed avoiding evening cycles, continuing fertility programs into the fall, reducing soil compaction, and raising the mowing height. All of these common cultural practices should relieve plant stress providing for better overall health.
Properly maintained turf should resist the infection, but be aware that the same areas may be affected year after year.
There are a few responses once you have detected rust, and the most common is to apply a nitrogen fertilizer. Proper fertility will promote more leaf growth, which will be a reason for more frequent mowing. This process will help the plant outgrow the disease as it tends to be a slow infection cycle.
In extreme cases, there are several fungicides labeled for use on rust. The DMIs and Strobilurons are particularly effective in control. Areas of historic infection can be treated preventatively with great success. This approach is more often taken on sod farms where infection can be widespread and detract from a sellable product.
Make sure to read and understand the label before using any pesticide. Feel free to reach out to the Ewing Technical Services Team with questions or comments.