Cool Season Turfgrass Disease Update

Alfredo Martinez, UGA Extension Plant Pathologist

It is time to scout for Brown patch (caused by Rhizoctonia solani) and Pythium blight (caused by Pythium spp). These diseases are often the most serious diseases on cool season grasses, especially on tall fescue and ryegrass                      

Brown patch can cause a foliar blight, which results in necrotic leaves and circular brown patches up to 4-5 ft. in diameter. High soil and leaf canopy humidity, and high temperatures increase disease severity. Higher than recommended rates of nitrogen in the spring promotes disease.

Management options include:

  • Avoid nitrogen application when the disease is active
  • Avoid infrequent irrigation and allow the foliage to dry
  • Mow when grass is dry
  • Ensure proper soil pH
  • Thatch reduction and
  • Improve soil drainage.

Pythium MartinezPythium blight has the potential to quickly cause significant damage to turfgrass. The disease starts as small spots, which initially appear dark and water-soaked. Affected turfgrass dies rapidly, collapses, and appears oily and matted. White, cottony mycelia may be evident early in the morning. The disease is driven by hot-wet weather, which correlates with an increased stress on the turf. Similar environmental and cultural factors that encourage brown patch also promote Pythium. Therefore, cultural practices for control of brown patch will also help to minimize Pythium blight development. A correct diagnosis is important because Pythium control requires specific fungicides.

Several fungicides are available for each of the diseases described above. Consult the Georgia Pest Management Handbook or the Turfgrass Pest Control Recommendations for Professionals for proper fungicide selection and usage. Read the label and follow proper guidelines.

For more information on these diseases visit:

For Brown Patch

For Pythium blight

Rose Rosette Virus – an emerging problem

Jean Williams-Woodward, UGA Plant Pathologist

Rose rosette virus is a damaging disease that is seeing an increase in occurrence across midwestern and southern states. Rose rosette has been described since the 1940s, but it wasn’t until 2011 that the causal agent was confirmed to be a virus spread by the ‘rose leaf curl’ eriophyid mite (Phyllacoptes fructiphylus).

Rose rosette disease on Knock-Out rose
Rose rosette disease on Knock-Out rose

Rose rosette virus was predominantly found in multiflora roses (Rosa multiflora) that now grow wild in many places and is considered an invasive/noxious weed. The wild multiflora roses were thought to be how the mite and virus spread into rose landscape plantings. What is causing greater concern is that the virus is now being seen in Knock-Out roses (see images). Knock-Out roses cover commercial and residential landscapes throughout the south because they are more disease resistance than other hybrid roses. The presence of the mass Knock-Out plantings provides an easy means for the mite and virus to spread from plant to plant and location to location. The increase in the amount of rose rosette showing up in Knock-Outs, which are all vegetatively propagated, has led to speculation that the virus may be spreading through nursery stock as well. This is possible, but currently I don’t have any evidence of this.

Symptoms of rose rosette virus mimic herbicide injury. In the past, we had no way of confirming the pathogen’s presence and often tried to rule out improper herbicide use. Symptoms include an increased and rapid elongation of new growth; abnormal reddish discoloration of shoots and foliage (see image above); witches broom (proliferation of new shoots); an overabundance of thorns; and deformed buds and flowers.

We are testing a molecular PCR test in the Athens clinic that can detect the virus RNA in order to confirm the disease. This test is the only way we can confirm virus infection.

If rose rosette virus is confirmed or suspected, control options are few. There is no cure for rose rosette. Roses growing near infected cultivated or wild (multiflora) roses have a high risk of infection.

To prevent infection:

  • Inspect new nursery stock for symptoms of infection.
  • Remove all multiflora roses from the area and increase plant spacing so rose plants will not touch each other to reduce mite spread.
  • If rose rosette is present, completely remove the infected plant by bagging and discarding or by burning.
  • There is some discussion on online garden forums and from rose breeders that just pruning off symptomatic canes/stems will remove the virus. There is not at present any scientific evidence that this will work. Therefore, the prudent recommendation I can give is to completely remove the infected plant.
  • A miticide can help reduce mite (and virus) spread; however, miticides labeled for spider mite control and those commonly packaged for homeowners are ineffective on eriophyid mites. If homeowners want to have their roses sprayed, then they should contact commercially licensed landscape professionals who can use (per communication with entomologist Will Hudson) Avid (or other abamectin generics), Floramite, Magus, and Forbid.