Just as the growing season is ending, a number of turfgrass diseases and pests may show up. “The challenge with diseases is that you’re usually chasing the problem,” says Pete Landschoot, PhD, professor of turfgrass science at Penn State University. “It’s not like weeds or insects where you can go clean things up immediately.”

Timing is another issue. A golf course is monitored so fungicide applications can be put down when disease-inducing weather, such as a string of hot, humid days, is forecast.

But if you’re an LCO with hundreds of residential lawns, you generally won’t have the opportunity to pre-treat. “Sometimes by the time you get out there, the weather cools or dries out, and the fungicide wasn’t necessary,” Landschoot says. “With disease, it’s often better to let it run its course, then clean up later with an application of fertilizer, for example.”

In addition, fungicides typically are more effective at preventing rather than treating disease. They usually must be applied regularly, which can become prohibitively expensive. Plus, curative applications won’t fix the appearance of turf that’s already affected. If you’re seeing a lot of damage, evaluate what cultural practices you can change. Do you need to cut back on nitrogen later in the season? Is there a drainage issue that invites problems? Are homeowners overwatering?

It’s also smart to educate clients. “People tend to get upset when they see spots and patches on their lawns, especially if you’re selling a program,” says Landschoot. Email a newsletter or make a blog post that explains what and when clients may see. Describe signs of a possible disease or pests, and highlight solutions, such as appropriate soil testing or other treatments.

If the lawn suffered minimal damage, a fall fertilizer application may be sufficient to help turfgrass fill in. Significant damage may require spot seeding by hand or slit seeding and overseeding for larger swaths. Ensure you have seed to soil contact; broadcasting over the top of the lawn does not work. For big seeding projects, a starter fertilizer may be beneficial with a 1:1:1 ratio, says Landschoot.

While pests are usually easy to identify, many diseases resemble each other. If you have any doubts about what you’re dealing with, contact your county extension office. Here’s what to be on the lookout for this fall:

Brown patch
Brown patch
Photo © Lee Miller, University of Missouri, Bugwood.org

What it looks like: Circular areas ranging from a few inches to 12 inches in diameter. Leaf blades turn brown. A grayish “smoke ring” may appear at the perimeter of active patches.

Brown patch is a very common fungal disease. “Although the fungus is always present in the soil, add enough rain, high nitrogen levels and the right weather conditions, and brown patch can develop,” says Robert Lane, PhD, professor of plant and soil science at Sam Houston State University. “Ideally, you want to ‘run out’ of nitrogen by fall. That lush grass in the fall encourages fungal growth with the right weather conditions.” Because it’s a foliar disease, crowns and roots are not affected. Thin turf typically recovers if it’s not otherwise stressed, but overseeding may be helpful.

Red thread
Red thread
© Florida Division of Plant Industry; Florida Department of Agriculture and Consumer Services; Bugwood.org

What it looks like: Circular patches of pinkish turf 4 to 8 inches in diameter with red tendrils that protrude from affected leaf blades.

Red thread affects cool season grasses including fescues, perennial ryegrass and Kentucky bluegrass when weather is wet and cool (from roughly 40 to 70 degrees). “Fine fescues can get hit pretty hard,” says Sam Bauer, associate extension professor at the University of Minnesota. “But it’s a foliar disease that won’t kill the plant, and turf usually recovers.” To reduce the chance of future outbreaks, ensure the turf has sufficient nitrogen, as this disease is often more severe in under-fertilized turf.

Dollar spot
Dollar spot
© Mary Ann Hansen; Virginia Polytechnic Institute and State University Bottom Photo

What it looks like: Dead straw-colored spots about the size of a silver dollar. In the early morning with dew, a white cobwebby growth may be seen.

Dollar spot thrives throughout the growing season in much of the country when there are extended dew periods and temperatures ranging from 50 to 80 degrees. Dollar spot blights leaf tissues but doesn’t kill roots or crowns. Mow grasses at the recommended height, instruct clients not to overwater, and ensure sufficient nitrogen as the disease is worse on under-fertilized turf. Thinning turf also may require renovation, Landschoot says.

Take all patch
Take all patch
© William M. Brown Jr., Bugwood.org

What it looks like: Irregular yellow, green or brownish patches occurring in clusters and ranging from 8 to 24 inches in diameter.

Take all patch is a root-infecting fungus that likes wet, cool (less than 65 degrees) soil. Roots are unable to support normal turf growth. “It typically doesn’t respond well to treatment,” says Lane. “Try adding mushroom compost, lightly raked over the area to encourage more biology in the soil. The goal is to increase the number of different microbial populations in the soil.” It’s believed these fungi don’t flourish in a naturally diverse microbial environment.

Pythium blight
Pythium blight
© Lee Miller, University of Missouri, Bugwood.org

What it looks like: Small, circular patches of collapsed or “greasy” leaves with a cottony white substance visible in the morning. Often first seen in low areas, it typically appears overnight.

Pythium blight is a fast-spreading disease that affects leaves and crowns and can kill plants. Large areas of turf can die within days. It’s most common with warm, muggy temperatures and rainy periods. “It can kill newly seeded ryegrass,” Lane says. “Most seed is treated with a fungicide which provides the young seedling a period of protection, but not forever.”

If you’re dealing with an outbreak, spray healthy grass to coat it well. Use a spray rig which atomizes the droplets into a fine mist; hand pump sprayers are not powerful enough to provide good coverage. Reseeding dead areas with a more pythium-resistant type of grass, such as tall fescue, also is recommended.

Armyworms
Armyworm
© John C. French Sr., Retired, Universities:Auburn, GA, Clemson and U of MO, Bugwood.org

What they look like: One- to two-inch-long caterpillars that love well-fertilized turfgrass, especially Bermudagrass.

Armyworm moths lay hundreds of eggs with seven to eight generations hatching out per year. You may not be able to see them when they first hatch, but after four to five days, you’ll notice caterpillars stripping off leaf blades, Lane says. If you choose to treat, most pesticides work well (read the label to be certain). “The most damaging aspect is that you’re going into winter with a weaker plant,” Lane says.

White grubs
White grubs
© PlazacCameraman | Thinkstock

What they look like: C-shaped white larvae that are just beneath the surface under thin patches of turf.

“White grubs, especially Japanese beetles, are the No. 1 pest we see in (the midwestern) part of the country in residential lawns,” Bauer says. If you didn’t do a summer application of preventive grub treatment, you can apply a contact insecticide such as carbaryl if grub pressure is intense. Consult the label, as products that are used to prevent grubs, such as imidacloprid, will not control the mature grubs.

The author is a freelance writer based in the northeast.