When we consider turf diseases in the fall, there are a number of pre-steps to act on before diving in with actual control measures. These can be best described as preparatory or foundational, much like reading the label before applying a fungicide or sanding and spackling a wall before painting it.
The foundational considerations of scouting, monitoring, identification, historical notations and evaluation are crucial to the success of effective turf disease control in the fall – or in any season for that matter.
Scouting and monitoring
Scouting is the term for frequent inspection and involves developing a routine of regular checks of critical turf areas, and examining any off-color or thin stands for the signs and symptoms of pests. Together, each scouting activity is characterized by monitoring, which is an organized, systematic approach to early detection.
Turfgrass disease signs (mycelial growth, spores) are often more difficult to spot than their symptoms (leaf blotches, rotten roots, thinning turf, yellowed leaves, etc). With other pests, such as weeds and insects, the signs – the actual insulting organisms – are usually more obvious. In these cases, invaders such as grubs, spurge plants and billbugs tend to stand out a bit more.
Yet, pests are pests and making observations in a pre-determined approach is of key importance for success. Also, by utilizing your historical records, you can guide your scouting to targeted areas in the landscape.
When overlooking a blighted-out area with no real distinct pattern, it can be a frustrating experience to hone in on the real causal agent. After all, the symptoms of one disease can often look like another at first glance.
As well, the presence of more than one disease can affect the overall appearance of the turf. Further compounding the identification process is the influence of abiotic factors such as compaction, heat stress, lack of irrigation uniformity, slope, nutrient deficiency and temperature-induced injury.
Considering the seasonality of a possible disease is a good start. Biotic organisms such as leaf spot, red thread, rust, powdery mildew, leaf spot and stripe smut are common in fall, while others such as summer patch, Pythium root dysfunction, brown patch and dollar spot are more often associated with early, mid- and late-summer infections.
Looking for specific clues on roots and shoots will help to narrow the diagnostic process down further as many times above ground symptoms are related to root injury.
Historical references are just one more clarifying tool in the process of fall disease control. In addition to the “looking at” procedures of scouting and identification, it’s helpful to “look back,” considering what has occurred previously at a particular point in the season.
When doing so, it’s important to keep the present weather and during the previous seasons in mind. Even though the current fall season may have produced classic patterns of warm days, cool nights and consistent rainfall, the previous ones may have been above or below average in any or all of these influences.
The most useful incidences of historical consideration is when current and past weather, traffic and maintenance levels are similar. In those situations, valuable insights can be obtained.
Fall turf diseases are a given. Another step in dealing effectively with them is to evaluate various pieces of the overall disease puzzle – the condition of the turf stand aside from any biotic or abiotic factors, the level of disease infection and the life cycle stage.
Coming on the heels of summer, where a half season of foot and cart traffic can extensively stress a turf stand, germinating spores of various diseases often take advantage of weakened plants, ones that offer less resistance to infection. On the other hand, if proactive cultivation, irrigation and fertilization has been performed, the turf is likely to be in good shape to handle fall turf diseases.
The level of infection, possibly characterized by the number of plants in a given stand that are infected, is also helpful in terms of management. If the infection is light, with scattered plants showing symptoms, the best course of action may be to delay treatment, especially if the weather is predicted to change to that which doesn’t favor its development.
If, on the other hand, it appears to be on the rise, then fungicide applications may be effective in preventing significant injury. The life-cycle stage should influence a treat or no-treat decision as well.
Newly infected leaves can often be sprayed, with the result of holding the disease in check and preventing spread to others. Full-blown infections are almost always much more difficult to control. In many of these situations, time and money is usually better spent on documenting the malady for future reference and renovation efforts rather than chemical disease control.
Here’s a list of fall turf diseases that are common on cool-season grasses and how they can be treated.
Easy to see, especially if you happen to be wearing white canvas shoes, heavily rusted turfs appear yellow or orange when seen from a distance. Clouds of orange rust spores are commonly observed discoloring pant legs and grass catcher bags as well as shoes.
Close-up examination of rusted leaf blades reveals the presence of orange to brick-red pustules. Spores within the pustules rub off easily when touched. Each one produces a vast number of spores, each capable of infecting a grass blade.
Rust management begins with the use of improved rust-resistant cultivars. Maintaining turf in a vigorous, but not lush condition through proper fertilization, early-morning watering and aeration to alleviate compaction are recommended to prevent injury from rust.
In many cases, turfs with significant rust problems are an indicator of low fertility. An application of nitrogen fertilizer can help a turf stand to recover from an outbreak of rust. In addition, regular mowing also reduces the potential for severe rusting in late summer and fall.
Fungicide applications should be considered on turfs with a history of rust infection. Generally, the initial application should be made in mid-summer, followed by one to additional treatments at three-week intervals. But the initial timing will depend on geography and rust overwintering each year.
Several products are available to choose from including azoxystrobin, chlorothalonil, mancozeb, propiconazole and triadimefon.
Powdery mildew occurs on several cool-season grasses including Kentucky bluegrass, turf-type tall fescues and fine fescues, primarily in shady locations on the golf course. The mildew fungus attacks the surface of the grass blades where it produces a white to light gray powdery growth.
Infected leaves become yellowed and later turn tan or brown. Turf in heavy shade looks like it has been dusted with flour or lime. Turf stands that are comprised of susceptible cultivars or newly seeded turf can become thinned by severe infection.
Powdery mildew develops in areas of dense shade where air movement is poor. Moderate temperatures, high humidity and cloudy weather favor outbreaks of mildew.
Because turf areas under large shade trees and along the north and east sides of buildings such as clubhouses, refreshment stands and bathrooms are particularly vulnerable to mildew infections, consideration of tree removal is a reasonable step.
Likewise, under the guidance of the right plant, right place principle, replacement of turfgrass with shade-adapted groundcovers may be a prudent option, especially if the area is not routinely in golf play.
If turf areas require renovation, incorporation of shade-tolerant tall fescue cultivars are helpful for powdery mildew control.
Fungicides can be used to treat high-value turf with a persistent powdery mildew problem. One or two applications in spring, summer and fall provides effective protection against turf loss from mildew. Effective products include myclobutanil, propiconazole and triadimefon.
Smut fungi infect a variety of grasses. It often shows up in late summer after initial infection in spring. When temperatures are in the 50- to 65-degree Fahrenheit range in spring, turf may become infected. Then during hot weather, disease activity ceases, only to return again once weather conditions are favorable.
Stripe smut causes grasses to exhibit a general decline, including stunted growth, yellowing and early death. Smut-infected plants usually occur in 6- to 12-inch circular patches. Blades in the patches show yellow stripes that turn gray, then black.
Over time, these symptoms often progress into leaves that shred and curl, followed by rupturing and release of masses of smut spores. High-value turf with a history of stripe smut can be treated with systemic fungicides such as fenarimol, triademefon and tebuconazole.
Leaf spot is commonly considered to be a spring and fall disease. Caused by Bipolaris and Drechslera spp., these fungal diseases are within the Helminthosporium leaf, crown and root disease complex. A variety of leaf spot symptoms accompany the stages of disease development.
Early symptoms are small, dark purple to black spots on the leaf blades. Older symptoms are round to oval spots with buff-colored centers surrounded by dark brown to purple margins.
Melting out starts out as black to purple spots on the leaf blades and sheaths. Infected leaf sheaths result in bases having a uniform dark chocolate brown, causing leaves to yellow and then drop from the plant. Looking at an infected stand from a distance, affected turf appears yellow and thin.
The most effective control program for leaf spot and melting out combines the use of improved cultivars, good management practices and fungicidal spray applications. Fertilization regimes that encourage steady vigorous growth, thatch management and watering in the morning to reduce the number of hours that the turf blades contain free moisture for disease development are appropriate measures.
Azoxystrobin, fludioxonil, fluoxastrobin, mancozeb, penthiopyrad, pyraclostrobin and vinclozolin are among the most effective products for these diseases. When necessary, application of a fungicide product beginning with the onset of cool conditions, followed by two to three additional applications spaced three weeks apart, is recommended.
The key components to outbreaks of red thread are cool, moist conditions, coupled with slow turfgrass growth. Drizzly days with temperatures between 65 and 70 degrees F are most conducive to its development.
Symptom patterns are circular to irregular patches with a pinkish to tan cast. The presence of uninfected leaves intermingled with infected ones often gives the patch a ragged or scorched appearance.
Infected leaves die from the tip downward, with the infection confined to leaves and leaf sheaths. During wet weather, leaves may become covered with pink gelatinous flocks of myclelium that sometimes bind the leaves together. Pink to coral threadlike fungal structures protrude from the tips of infected leaf tips as branched, antler-like appendages – hence the name red thread.
Maintaining an adequate and balanced fertility program can help prevent severe infection. When disease pressure is high, collecting grass clippings can reduce the spread of the fungus.
On turfs with a history of red thread infection, starting a preventive fungicide program when weather conditions are favorable will reduce the damage. Fungicides that limit infection include azoxystobin, fenarimol, iprodione, mancozeb, myclobutanil, propaconizole and thiophanate-methyl.