Lawn care: Fall turfgrass diseases to watch for

Updated Sep 28, 2018
Rust is a fall disease of Kentucky bluegrass or perennial ryegrass, infecting turf that is slow-growing from limited irrigation and/or nitrogen. Photo: BayerRust is a fall disease of Kentucky bluegrass or perennial ryegrass, infecting turf that is slow-growing from limited irrigation and/or nitrogen.
Photo: Bayer

It is officially the fall season and with it comes homeowner beliefs that there’s nothing left to do in the yard.

Yet after the stress of summer, your client’s turfgrass is more vulnerable than ever to certain fall lawn diseases, so it’s your job to educate them on the need to keep up the good fight and continue to prioritize proper lawn care.

 â€śMaximizing plant health year-round is critical for minimizing diseases in lawns all season long,” says Zac Reicher, Ph.D., Bayer Green Solutions Team specialist.

Common diseases to look for

For the most part, cool-season grasses don’t have to deal with many diseases in the fall, according to Reicher. One of the few diseases that can be common in early fall is rust.

Rust is a fungal disease that appears as yellowish-orange powder on grass blades. Low fertility and low water availability can slow down turf growth, allowing rust to appear. Excess rain can deplete available nitrogen making rust more likely in cool-season turf.

“It is most common on Kentucky bluegrass or perennial ryegrass with dry weather and poor growing conditions,” says Jamie Breuinger, technical leader for Corteva Agriscience, Agriculture Division of DowDuPont, Turf & Ornamental division. “Although the disease is mostly cosmetic, homeowners can be annoyed with the yellow/orange pustules that can leave a distinct orange color on your shoes. To address this issue, it is recommended to increase the growth of the turfgrass through fertilization and irrigation.”

Another fungal disease cool-season grasses can experience in the fall is necrotic ring spot. This disease is characterized by ring-shaped patches of dead or dying turf. These patches may at times coalesce, or they may stand out as individual dead rings. It is most commonly found in Kentucky bluegrass.

Environmental conditions for necrotic ring spot vary with it being more severe in some locations during spring and fall, while in other regions it only appears in midsummer.

It tends to be more problematic in lawns with significant thatch or poor soil structure, according to Reicher.

Large patch affects almost all warm-season grasses, including St. Augustine in this picture, with infection in the fall well before symptoms are usually seen in the spring. Photo: BayerLarge patch affects almost all warm-season grasses, including St. Augustine in this picture, with infection in the fall well before symptoms are usually seen in the spring.
Photo: Bayer

As for warm-season grasses, fall lawn diseases are far more problematic as they are entering the slower growth period from the fall to the spring.

Some of the diseases that are commonly spotted are large patch and take-all root rot.

Large patch features circular patches that turn yellow, then reddish brown, brown or straw-colored as the grass dies. According to Matt Giese, technical services manager at Syngenta, large patch can develop on zoysiagrass during wet, cool fall weather.

Take-all root rot causes brown dead spots in turfgrass and early symptoms are patches of turf appearing yellowish green. If left unchecked, it will result in severe thinning of the grass.

“Last year, Hurricanes Harvey and Irma caused tremendous problems with take-all root rot in warm-season lawns, but we have been lucky in 2018 with no major outbreaks in warm-season turf to date,” Reicher says.

Last but not least is dollar spot, which is prevalent in the fall and affects both warm- and cool-season grasses. Dollar spot is recognizable by tiny yellow spots on individual blades and as the grass dies, straw-colored spots 2 to 3 inches in diameter begin to appear in the lawn.

This disease can become widespread if summer conditions were harsh and supplemental fertilizer was not applied, according to Giese.

Dealing with ID difficulties

When it comes to identifying some of these fall lawn diseases, it can be challenging. Reicher says necrotic ring spot is the hardest to ID in cool-season turf, as it can be mistaken for drought damage, white grubs or fairy ring.

“Necrotic ring spot is a root-infecting disease that does not produce above ground mycelium or lesions on turf leaves, but it does produce characteristic frog-eye patterns in the turf with thin or dying rings up to three feet in diameter with healthy turf in the center,” he says.

Because turf diseases may not match their textbook appearance, Giese advises enlisting the help of your local turf disease diagnostic clinic to help identify the issue.

Sometimes it can also be hard to determine if the aesthetic issues your customer’s lawn faces are the result of a fungus or just poor cultural practices.

“Diseases or other biotic problems will typically form irregular patterns that may follow shade, traffic or soil wetness patterns,” Reicher says. “Conversely, man-made problems like inconsistencies in application or improper irrigation will be in more regular patterns and may be in straight lines depending on the cause.”

Giese adds that diseases typically show foliar patterns of necrosis, and moisture stress symptoms appear consistent and evenly brown.

Best practices

In order to reduce the risk of fall lawn diseases, there are a number of best maintenance practices landscapers can follow.

“Most, but not all, diseases in turf are a reflection of previous maintenance, both long- and short-term,” Reicher says. “Rust is a classic example of a disease attacking almost exclusively under-fertilized Kentucky bluegrass or perennial ryegrass lawns.”

A majority of the cultural practices are pretty straightforward, including mowing frequently enough at the highest recommended height for different grasses. Reicher says to avoid removing more than 1/3 of the leaf blade at a time.

Another important factor is monitoring irrigation and avoiding overwatering.

“All lawn diseases are favored by moisture extremes (too wet or too dry), so it is important to monitor irrigation distribution and regularly adjusting irrigation frequency and volume throughout the year,” Reicher says.

Matt Giese Photo: SyngentaMatt Giese
Photo: Syngenta

As you go into fall, there may be turf loss from various summer stresses like drought, heat, disease, traffic or insects. Applying the proper amount of fertilizer can promote recovery.

“Lawn care professionals need to think of fall as a time for turf renewal for cool-season grasses,” Breuninger says. “Fertilization at this time will help to stimulate growth and turf recovery. For management of Kentucky bluegrass, aeration or raking out the dead debris will help healthy turf spread into damaged areas. As a good rule of thumb, if there is more than 50 percent thinning of the turfgrass, reseeding may be needed.”

Speaking of dead debris, managing thatch and maximizing sunlight and air movement are two other important maintenance practices to follow.

“Established turfgrass builds up thatch over time and creates perfect breeding grounds for diseases,” Giese says. “Aerification, de-thatching or power raking can help reduce environments conducive to disease.

As for what to do when there is a lawn disease already present, Giese says treating turfgrass depends on the disease present.

“Foliar diseases are easier to control because fungicides can directly contact the pathogen on the plant’s surface,” he says. “Applying at first detection can be effective. However, soil-borne diseases require a preventive approach since fungicides need to absorb into plants long before symptoms show for optimum control. Curative fungicide applications to soil-borne diseases are generally not effective.”

When dealing with large patch or take-all root rot in warm-season grasses, Reicher suggests applying fungicides like Armada preventatively for effective control.

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