Methods to Maximize Efficacy of Turfgrass Fungicides

Alfredo Martinez, UGA Plant Pathologist

Weather conditions have been conducive for turfgrass diseases. We have received numerous calls and emails about proper control strategies, especially on the appropriate selection of turfgrass fungicides and their efficacy. Some ways to maximize the efficacy of turfgrass fungicides include:

  • Read carefully and follow the label directions before applying fungicide.
  • Apply fungicides at the rate specified on the label.
  • Always follow instructions for re-entry to the area.
  • Fungicides are not equally effective on all diseases. Proper fungicide selection is very important for disease management.
  • The best control is achieved by applying fungicides preventively (before disease is present).
  • Use compatible tank mixes at recommended label rates.
  • Use proper sprayer, nozzles and pressure to deliver appropriate coverage of fungicides. Flat fan or swirl chamber (raindrop) nozzles are recommended for turfgrass fungicide applications.
  • Avoid turfgrass stress (drought or temperature) before or at the time of application. This could interfere with maximum fungicide uptake, activity and efficacy.
  • Fungicides should be sprayed when air temperatures are between 60°F and 85°F (15°C and 29°C) for best results.
  • Fungicides should stay on the turfgrass foliage for at least 6 hours for most effective control. Delay mowing and other cultural practices as much as possible to give the fungicide a chance to work (for proper mowing frequency follow the one-third rule).
  • Use enough water when applying fungicides for adequate coverage. Usually 2.0 gal water/1000 sq. ft. should give adequate coverage and deposition. Some fungicides have to be watered-in for proper placement to ensure adequate activity.
  • Do not apply fungicides when conditions are windy to avoid drift and poor coverage. Wind velocity tends to be the lowest early in the morning and late in the afternoon.
  • Be patient if an application appears to have produced no results. Some fungicide application results can be seen months later.
  • Use fungicides judiciously and sparingly.

Some notes on Fungicide Resistance

Fungi sometimes develop resistance to particular fungicides, especially when a product is used repeatedly without alternating with chemically unrelated fungicides. When fungicide resistance develops, there is no value in increasing rates, shortening intervals between sprays, or using other fungicides with similar modes of action.

Fungicide resistance has been confirmed in a few instances for each of the following turfgrass diseases and fungicide groups:

  • Dollar spot against benzimidazole fungicides (thiophanate methyl) and DMI fungicides (propiconazole)
  • Gray leaf spot against strobilurin (QoI) fungicides (e.g. azoxystrobin, etc.)
  • Anthracnose against benzimidazoles (thiophanate methyl) and strobilurins (QoI) (azoxystrobin, etc.)
  • Pythium blight against phenylamide fungicides (mefenoxam)

Benzimidazoles (e.g. thiophanate methyl) and phenyl amides (e.g., mefenoxam) have the highest risk of resistance.

Strobilurins have a moderately high risk of resistance

DMIs and the dicarboximides (e.g. iprodione) have a moderate risk

Nitriles (e.g. chlorothalonil), aromatic hydrocarbons (e.g. PCNB), and dithiocarbamates (e.g. mancozeb) have a low risk of resistance.

Several general strategies are recommended to minimize the risk of fungicide resistance.

  • First, don’t rely on fungicides alone for disease control.
  • Avoid using turfgrass varieties that are highly susceptible to common diseases and follow good disease management practices.
  • Also, limit the number of times at-risk fungicides are used during a growing season and alternate at-risk fungicides with fungicides in a different chemical group (those with a different FRAC numeric code).
  • When using an at-risk fungicide, tank-mixing it with another fungicide from another chemical group (different mode of action) can also reduce the risk of resistance.

These are general principles that can help to reduce, but not eliminate risk. A fungicide-resistant pathogen population can still develop when these principles are practiced. Refer to product labels before tank-mixing products to ensure compatibility and to avoid phytotoxicity.

For major chemical group description, see the Georgia Pest Management Handbook – turf disease control section.

Emerald Ash Borer found with a foothold in North Georgia

EAB Debbie Miller, USDA Forest Service
Emerald Ash Borer, Debbie Miller, USDA Forest Service,

Sandi Martin and Merritt Melancon,  University of Georgia 

For years foresters and invasive insect experts have been on the lookout for the arrival of an unwelcome guest in Georgia. Now that it’s here, they hope the public will help restrict its spread within Georgia.

The small, iridescent-green beetle has killed millions of ash trees across a wide swath of Canada and the upper Midwest since it was first detected in 2002. The emerald ash borer — Agrilus planipennis— has spread south and west from infested areas over the last decade.

In July, researchers found adult emerald ash borers in survey traps in DeKalb and Fulton counties. A follow-up ground survey found larvae in nearby ash trees, confirming an established emerald ash borer infestation.

EAB larvae David Cappaert, Michigan State University
Emerald Ash Borer larvae in tree, David Cappaert, Michigan State University,

Since 2005 University of Georgia invasive species experts have conducted an extensive trapping program in Georgia to screen for the emerald ash borer.

Georgia’s five species of native ash trees usually grow along stream banks. While ash only makes up about 1 percent of Georgia forests, they play an integral role in preventing the erosion of stream banks and keeping silt out of natural waterways. Ash is also a popular landscape tree, with 2.9 million trees planted around Georgia homes, businesses, parks and greenways. The value of these city trees in Georgia is estimated to be around $725 million.

EAB exit hole Penn. Dept. of Conservation & Natural Resources - Forestry Archive
Emerald Ash borer creates a D-shaped exit hole, Image from Penn. Dept. of Conservation & Natural Resources – Forestry Archive, Bugwood.rog

Although the adult beetle is an active flyer, it is believed that the primary way the beetle spreads is by hitching a ride on infested ash firewood, logs and nursery stock. Emerald ash borer larvae kill ash trees by burrowing serpentine tunnels in the inner layers of bark, preventing the tree from transporting water and nutrients to and from the tree canopy.

The Georgia Invasive Species Task Force will launch a public outreach plan to try to curb the spread of this pest in the near future. This task force consists of the Georgia Department of Agriculture, the Georgia Forestry Commission, UGA, the Georgia Department of Natural Resources and the USDA Animal and Plant Health Inspection Service.

People can help slow the spread of this beetle through Georgia by not moving firewood and by helping others to understand how dangerous it can be to move firewood from one area to another.

“To prevent the spread of emerald ash borer, it is important not to move firewood in which the insect can hide,” said Kamal Gandhi, associate professor in the UGA Warnell School of Forestry and Natural Resources. “Buy local firewood, whether camping or for your home.”

To help reduce the spread of the emerald ash borer in Georgia, homeowners with ash trees should have a certified arborist check their trees for signs of emerald ash borer infestations.

Suspected infestations should be reported immediately so that foresters or arborists can understand how the infestation is spreading. This will aid in the development of effective methods to reduce its spread and impact.

“The faster (scientists) can track the spread of the insect, the faster they can work to stop it,” said Joe LaForest, integrated pest management and forest health coordinator at the UGA Center for Invasive Species and Ecosystem Health.

The public can report suspected infestations by:

For more information about the emerald ash borer and how to protect ash trees, visit

For more information about spotting signs of emerald ash borer infestations, watch this.

(Sandi Martin is the public relations coordinator with the University of Georgia Warnell School of Forestry and Natural Resources. Merritt Melancon is a news editor with the University of Georgia College of Agricultural and Environmental Sciences.)

Other information:

Emerald ash borer factsheet

Emerald Ash Borer 2013 Update

Frequently asked questions about EAB in Georgia

Destructive tree pest discovered in Georgia

New bee advisory on neonicotinoid pesticides

See original article from the Southern Region IPM News here

In an ongoing effort to protect bees and other pollinators, the U.S. Environmental Protection Agency (EPA) has developed new pesticide labels that prohibit use of some neonicotinoid pesticide products where bees are present. (This announcement affects products containing the neonicotinoids imidacloprid, dinotefuran, clothianidin and thiamethoxam. – Editor’s note)

“Multiple factors play a role in bee colony declines, including pesticides. The Environmental Protection Agency is taking action to protect bees from pesticide exposure and these label changes will further our efforts,” said Jim Jones, assistant administrator for the Office of Chemical Safety and Pollution Prevention.

Bee advisory box from EPAThe new labels will have a bee advisory box and icon with information on routes of exposure and spray drift precautions. Today’s announcement affects products containing the neonicotinoids imidacloprid, dinotefuran, clothianidin and thiamethoxam. The EPA will work with pesticide manufacturers to change labels so that they will meet the Federal Insecticide, Fungicide, and Rodenticide Act (FIFRA) safety standard.

In May, the U.S. Department of Agriculture (USDA) and EPA released a comprehensive scientific report on honey bee health, showing scientific consensus that there are a complex set of stressors associated with honey bee declines, including loss of habitat, parasites and disease, genetics, poor nutrition and pesticide exposure.

The agency continues to work with beekeepers, growers, pesticide applicators, pesticide and seed companies, and federal and state agencies to reduce pesticide drift dust and advance best management practices. The EPA recently released new enforcement guidance to federal, state and tribal enforcement officials to enhance investigations of beekill incidents.

More on the EPA’s label changes and pollinator protection efforts:

View the infographic on EPA’s new bee advisory box:

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.