Rust

Photo: Alfredo Martinez While some turfgrass diseases are impossible to identify with the naked eye, rust is not one of them. Walking through an infected area will often leave an orange residue on shoes, hinting that the discoloration is a rust problem.

“From a distance, the disease can sometimes be mistaken for other diseases. However in a closer look, symptoms and signs of the disease are unique,” says Alfredo Martinez, University of Georgia associate professor/extension plant pathologist.

Rust, which occurs in most turfgrass species and is especially problematic on Kentucky bluegrass, ryegrass, tall fescue and zoysiagrass, isn’t one of the more harmful plant diseases, but it can have large outbreaks and it can be unsightly. Lawn & Landscape asked Martinez how to identify, prevent and control rust diseases in turfgrass.

How does rust form?
Rust is a disease caused by a variety of related fungi, specifically by fungi belonging to the genus Puccinia and/or Uromyces. Rust infections occur on slow-growing turfgrass, particularly those areas with low nitrogen levels, imbalanced soil fertility, plant water stress, shaded-low lighted areas and soil compaction. Rust, as a whole, causes relatively minor turfgrass stand losses. However, the disease has the potential to cause severe outbreaks in stressed, weakened turfgrass areas.


How can LCOs identify rust?
From a distance, rust-infected turf appears to have a yellow-green, orange cast. As the disease progresses, symptoms occur in a diffuse, irregular, yellow-reddish pattern.

Because of the amount of spores produced on turfgrass leaves, shoes and clothes of lawn care operators are stained with an orange tinge while walking through infected areas. One easy way for lawn care operators to detect rust is by rubbing their fingers along the leaf blades. A yellow, orange and powdery material adheres to the fingers. This material is made of bright colored spores.


How can it be prevented and controlled?
Rust thrives on stressed turfgrass areas. Mainly in areas with an imbalanced soil fertility, compaction and low nitrogen; therefore, rust severity can be greatly reduced by maintaining a healthy, vigorous turf stand. Maintain recommended soil fertility and soil pH levels. Following nitrogen fertility recommendations is a critical factor in controlling rust in warm season grasses.

Follow proper irrigation practices, avoiding irrigation during early evening will limit the spread of the disease by diminishing the chance of extended dew periods. Proper mowing heights and removal of clippings can help to reduce inoculums levels. Improve air circulation and light penetration on shaded, closed areas.

Fungicides are rarely suggested on home lawns or landscape turfgrass areas for rust control. In rare cases, fungicides are warranted. Fungicides should only be consider as remedial treatments when cultural practices fail to prevent an outbreak.

In the few instances that fungicides are warranted, what active ingredients are effective? There are a variety of fungicides that are effective against turfgrass rust diseases. Their use varies depending on the geographical region and state to state, so always follow the label directions for use.

The fungicide families/groups named demethylation inhibitors (DMI’s) fungicides, the QoI (strobilurins) fungicides, or the benzimidazole fungicides, to name a few, are very effective against rust. I strongly suggest focusing on cultural practices.

The author is an associate editor at Lawn & Landscape. She can be reached at clawell@gie.net.