Fungicides

Dave Gardner, associate professor, Turfgrass Science – Ohio State

• Leaf Spot
• Powdery Mildew
• Rust
• Red Thread
• Dollar Spot

This is based on frequency of occurrence and not on severity at occurrence. They are almost never treated on a home lawn. Having said this there are others that manifest less frequently but when they do it’s a problem like you might be inspired to apply a fungicide.

• Brown patch on Tall fescue
• Summer patch on Kentucky bluegrass, but by the time you see it it’s too late to apply a fungicide
• Necrotic Ring Spot, but by the time you see it it’s too late to apply a fungicide

And you may occasionally see grey snow mold, though I don’t know that it causes real loss of density in a residential lawn.

Bruce Martin, Clemson
It depends on the turf, of course. For instance:

Tall fescue: brown patch and Pythium blight with a third possibility of gray leaf spot under extreme heat/humidity.

Ryegrass is also susceptible to the same diseases as tall fescue in hot humid environments.

Kentucky bluegrass: Melting out, Summer patch are the primary diseases

Bermudagrass: Bipolaris leaf spot and maybe dollar spot if underfertilized.

Zoysia: Rust perhaps, dollar spot if underfertilized. But next fall if wet conditions, lRhizoctonia arge patch will be active and show symptoms in the following spring.

Centipedegrass: large patch if overwatered and over-fertilized.

St. Augustinegrass: in summer, gray leaf spot. Late summer, take-all root rot. Fall, winter and spring in cool wet conditions: large patch.

For almost all of these, managing thatch and preventing compaction are primary cultural practices that are beneficial. Watering when the grass needs it, not when the irrigation timer happens to go off, which keeps leaf wetness at a minimum and helps reduce the foliar diseases. Fertilization based on the requirements of the particular grass, which varies. Not too much, not too little.

There are many sources of information for specific fungicides for each of these diseases, if needed. The list is long but recommendations are specific and may vary depending on location.

Nathaniel Mitkowski University of Rhode Island
1. Dollar Spot (Sclerotinia homoeocarpa). This is the most common disease on turf. It tends to be worse the lower you cut the grass and the more uniform the grass so weedy lawns generally look OK with a little bit of diease. Tends to be late spring into September but can occur earlier or later, depending on the season. Applications of many different fungicides on a 21 day schedule can keeps lawns fairly clean of disease, along with good water management and regular fertilization (not too much or too little of either).

2. Brown Patch (Rhizoctonia solani). This disease is common when hot and humid. It is relatively easy to control with fungicides and fortunately it does not do much extensive damage but it can look very ugly. If you happen to have a cool or dry summer, the disease is generally not a problem. Areas with poor air movement and too much water are most impacted, as are the mid-atlantic and southern states.

3. Pythium Blight (Pythium). Pythium is favored by the same conditions that incite brown patch but it is far more destructive and can kill significant amounts of turf in a short time. If this disease has been a problem in the past, preventative fungicides applications need to be undertaken as soon weather favorable for the disease is expected.

4. Summer Patch (Magnaporthe poae). This disease is very different from the rest, it is primarily a soil-borne pathogen and extremely difficult to control. It starts with wet conditions and progresses into the summer, devouring roots. It is primarily a problem on annual and Kentucky bluegrass and by the height of the summer, can leave softball-sized or bigger dead patches across a lawn. It is more common in wet environments and can be very difficult to discern from insect damage or other issues on lawn turf. If this disease has been a problem in the past, it will require either a very aggressive and expensive fungicide program or a conversion to perennial ryegrass or other nonhost turf.

5. Rusts (Puccinia spp.). Rusts are very common in the fall, especially when conditions are humid. They typically do not cause a lot of damage but they can make sod unsaleable and are somewhat unattractive. Rusts can be treated with fungicides but the best approach in a lawn setting it to either ignore it or try and improve sunlight and air movement. Adequate fertilization can help minimize the effects of the disease but will not eliminate it.

I have been out of my office fulfilling other academic and extension responsibilities. I hope is not too late and you can still use the information.

Your question on top turfgrass diseases could have several answers depending on geographical location, grass species or time of the year.

Alfredo Martinez-Espinoza, Associate Professor and Extension Plant Pathologist Turfgrass/Small Grains/Non-Legume Forages, University of Georgia

To cover these variables I would say:

Warm season grasses top diseases that lawn care operators could see now and in the next several months are:

• Spring Dead Spot (by Ophiosphaerella spp)
• Large Patch (by Rhizoctonia spp)
• Dollar spot (by Sclerotinia homoeocarpa)
• Take all root rot (by Gaeumannomyces spp)
• Cool season grasses (Kentucky bluegrass mostly)
• Summer Patch (by Magnaporthe poae)
• Necrotic ring spot (by Leptosphaeria korrae)
• Bipolaris leaf spot (Bipolaris spp)
• Cool season (tall fescue)
• Brown patch (by Rhizoctonia spp)
• Pythium Blight (by Pythium spp)