Be Prepared for Summer and Fall Diseases

9/4/2012

by John C. Fech 

No matter the setting, turf disease is a challenging malady. The traditional disease triangle components of host, pathogen and environment influence the degree of damage that's experienced from north to south, in residential lawns and shopping malls and on all species of turfgrass. When season of year is added to the mix, some considerations change and some remain the same.

One difference between many spring and fall scenarios is the expectation of the customer for the outcome or the aesthetic appeal of the turf. In fall, the tendency (at least in the mind of some customers and property owners) is to just sort of give up when the turf starts to look a little stressed and not take any control measures-until their turf or commercial property is damaged as a result, and then it's your fault, not theirs.

Inspect regularly
Late summer and fall turf diseases are weather-dependent maladies. Because weather conditions often change quickly, an outbreak can suddenly erupt. The first step in dealing with these causal agents is to regularly inspect customers' lawns. Some people call it scouting and others call it monitoring. Whatever you call it, you or your trained technicians should always be on the lookout for turf damage when you're on clients' landscapes.

An inspection is a thorough, close-up look for disease symptoms. There are several ways to go about inspection, with the nature of the variety of services provided being the best way to determine the best approach. For example, if the customer has hired your company to provide mowing, fertilization and weed control, there's no reason why technicians can't recognize problems as they work. It's not essential that they become turfgrass pathologists, just that they are able to identify that something's wrong and requires a more thorough investigation. 

Another opportunity for inspection can be taken when the account calls for fertilization only. When fertilization applicators finish with product dispersal and are blowing material from impervious surfaces such as sidewalks and driveways back to the turf areas, observations about odd-looking turf can be noted and communicated to other staff better versed in diagnosis.

Regardless of the arrangement, regular inspection is a good idea and, if possible, bill for it. The value of the experience and training of a quality landscape maintenance company's staff is important and shouldn't be taken lightly, and especially not just given away. Can you factor bi-weekly turf diagnosis into the overall maintenance budget of your clients, or at least those that have experienced damage caused by diseases previously? Some diseases tend to occur on the same properties regularly, if environmental conditions are ripe for them.

Stem rust
Of all the late summer and fall turf diseases, stem rust is perhaps the easiest to identify. Rust-infected leaves appear yellow or orange, even from a distance. When leaves are disturbed, clouds of orange rust spores can quickly discolor shoes, mowers, grass catchers and pant legs.

When looking closely at affected leaves, the presence of orange or brick-red pustules are evident. The spores within the pustules rub off easily when touched. Each pustule contains many spores, capable of infecting nearby grass blades. Under ideal conditions of warm days and moderate night temperatures common in late summer or early fall, this pathogen can spread rapidly. Rust-affected turf becomes weak and thin, and unable to resist other common diseases or various environmental stressors.

The incorporation of rust-resistant cultivars greatly enhances a rust control program. Check with local university extension specialists and/or the National Turfgrass Evaluation Program (NTEP) for information on specific cultivars. Regular mowing and removal of grass clippings is also helpful. Heavy infections may require the application of fungicides such as azoxystrobin, chlorothalonil, fluoxyastrobin, mancozeb, propiconazole, thiophanate-methyl, triadimefon or trifloxystrobin.

Leaf spot/melting out
While this is most often thought of as a springtime disease, a reoccurrence is possible in some years, especially when cool and moist conditions are prevalent for several weeks in early fall. Initial symptoms are small oval purplish to black spots on leaf blades. Over time, the spots become more numerous and appear as beige-colored centers surrounded by dark brown or purple margins. Eventually, the "melting out" stage develops as the disease works its way into the sheaths and crowns of the plant. From a distance, affected turf looks light brown and thinned.

As with rust, the most-effective control measure that one can take is to incorporate disease-resistant cultivars into the turf through re-seeding or re-sodding. Moderate fertility levels and early morning watering are helpful as well. When severe symptoms appear, consider applications of azoxystrobin, chlorothalonil, fludioxonil, fluoxastrobin, iprodione, mancozeb, propiconazole, thiophanate-methyl, tritfloxystrobin or vinclozolin.

Red thread
Like leaf spot, red thread is often thought of as exclusively a springtime disease, however, after disease activity ceases during hot, dry summers, it may resume in the fall. The pathogen survives the summers as sclerotia and dormant mycelium in infected turf plants and is often spread by mowing equipment, especially during damp weather conditions. Red thread is a good descriptor for this disease, as symptoms appear as patches with a pinkish to tan cast.

The presence of uninfected grass blades intermingled with infected leaves gives the patches a scorched or ragged look. Individual blades die from the tip downward, affecting mostly the leaves and leaf sheaths. In moist autumn seasons, leaves become covered with pink gelatinous strands of mycelium that often stick together.

Removing clippings and providing a balanced fertility application regime help prevent severe infection occurrences. On turf with a history of red thread, begin a preventative fungicide program when temperatures drop into the 60s and upper 70s, especially if infection occurred in the spring. Products such as azoxystrobin, chlorothalonil, fenarimol, flutolanil, iprodione, mancozeb, myclobutanil, polyoxin, propiconazole, pyraclostrobin, triadimefon, triticonazole and vinclozolin can be applied. 

Stripe smut
Stripe smut is a cool weather disease that shows up in spring and sometimes in fall. Like red thread, once a plant or group of plants is infected, it has a greater tendency to resume growth later in the season. As well, smut spores can remain dormant in the thatch for up to three years. Infected plants take on a generally yellowed and unthrifty appearance, usually resulting in an early death. Smut-infected plants usually occur in 6- to 12-inch circular patches, and can coalesce to form larger areas. Leaves on infected plants show yellow stripes that later turn grey and black. Eventually, the leaves shred and curl.

In spring, removing clippings of infected plants will reduce the overall level of inoculum as smutted leaves release masses of spores into the thatch after they curl. Traditional best management practices for turf are also recommended. Applications of fungicides such as fenarimol, propiconazole or triadimefon should be applied prior to the onset of disease symptoms for best results.

Powdery mildew
Powdery mildew appears in the turf as if the leaves were dusted with flour, casting a white soft hue on them. In most landscapes, it develops in shady areas and/or where air movement is insufficient. Cloudy weather and high humidity favor its occurrence. Turf areas under shade trees and the north and east sides of houses or buildings are likely locations for infection. Affected leaves turn from white to yellow and eventually die, causing a thinning of the stand.

Control can best achieved through a change in the landscape to improve sunlight penetration and increase air flow across the sod. Removing trees and thinning is a drastic step, and not recommended; the effect is usually temporary as well. Better results will be achieved through changing the landscape design to put shade-tolerant groundcovers, perennials and shrubs in place of turf. If clients insist on retaining turf, fungicides such as myclobutanil, propiconazole or triadimefon provide effective control.

Slime mold
Though not a true disease, this problem is a real concern for the uninformed customer or property owner. The good news is that no control is necessary, other than regular mowing to remove the sack-like spore enclosures that most customers find offensive. Slime mold fruiting bodies create a slimy growth that dries into a powdery mass that coat the grass blades. Fortunately, they are more of a curiosity or nuisance than a threat to the turf.
 


The author is a horticulturist and certified arborist located in Omaha, Neb.

Photos: Slime mold, powdery mildew and rust photos courtesy of John Fech. Stripe smut photo courtesy of UNL. Red thread photo courtesy of Lane Treadway, NCSU.