Sports Field Management - May, 2012
Determine the cause, treat the effect
The fields are striped and ready to go, the last-minute adjustments are being taken care of, the players are arriving for pregame warm-up drills, and as the crew is busy making the seed and sand mixture to fill divots, you notice that a few parts don't look quite right. The last thing you need before an important soccer tournament is a major pest problem. What do you do? Many options exist, from popping a couple of aspirin to heading to the train station and asking the ticket agent how far $21.50 will take you. Instead, resolve to adopt a problem-solving strategy that improves your overall ability to forecast, diagnose and treat disease, environmental and insect problems in a strategic and cost effective manner. Following is a comprehensive approach.
Dollar spot is often associated with low-nitrogen sports fields (left). Stem and leaf rust are common fall diseases (right).
PHOTOS BY JOHN C. FECH, UNL.
There are many ways to go about diagnosing turf diseases on sports fields. Each has its pros and cons, so it's wise to use a variety of methods to avoid focusing too closely on any one causal agent.
First, you can use the previous few years of observations as a historical guide. We're not sure who they were, but the authors of the phrases, "the best teacher is your own mistakes" and "the definition of insanity is doing the same thing over and over again while expecting a different result," are certainly on to something. History is not only useful when things don't go as planned; more often than not, applications of fertilizer and pesticides, aeration operations and overseeding attempts do achieve the desired outcomes. A record book filled with detailed notes on products, locations of pest outbreaks, application equipment, etc., is a helpful tool in overall disease management. Historical perspectives and remembrances of fellow sports turf managers shared over coffee can be equally useful.
Next, when considering turf diseases, think roots and shoots. There are root diseases and shoot diseases, and a few that are both. Knowing the symptoms of each goes a long way towards narrowing down the number of possibilities. At a bare minimum, making observations about which parts of the plant seem to be affected the most - odd looking spots on the leaves, mushy roots, interesting patterns on the field - will provide essential information as observations are matched to disease field guides.
Accurate identification of the pathogen responsible for the symptoms before pest control agents are applied is important. When an incorrect diagnosis is made, products chosen for what was thought to be the target pest will often not control the problem. Utilizing pest identification resources will greatly reduce misidentification. The following books are good resources, as well as the many identification tools offered by land grant universities:
- "Compendium of Turfgrass Diseases," by Smiley, Dernoeden and Clark
- "Managing Turfgrass Pests," by Watschke, Shetlar and Dernoeden
- "Integrated Turfgrass Management for the Northern Great Plains," by Baxendale and Gaussoin
- "Controlling Turfgrass Pests," by Shurt- leff, Fermanian and Randell
Timing is, as they say, everything. This is obvious as you watch a pass from a quarterback to a split end. With regards to diseases, timing is a very important control factor because in the life cycle of each disease, there is an optimal point for treatment. Be sure to apply a fungicide product at the most vulnerable stage of the cycle to get the greatest degree of efficacy. It is equally important to make sure you are targeting the correct zone. If it is a root disease, you need to make sure you deliver the fungicide to the roots, as fungicides will not move down.
Timing is also important in that most diseases are favored by certain environmental or weather-related conditions. As such, the season of the year becomes crucial in the consideration of potential pathogens. As the year progresses, diseases also progress; snow molds give way to leaf spot, powdery mildew and red thread, then dollar spot, melting out and necrotic ring spot, to Pythium root dysfunction, summer patch and brown patch, and finally to stem rust and stripe smut. Knowing which diseases are likely to occur at what point in the growing season is a powerful tool in disease management.
A fresh perspective
Take a step back, look from the outside in - gain a fresh perspective somehow. Perhaps climb to the top of the bleachers and look down over the field. It's quite possible that factors beyond your control have led to the demise of the turf. Many abiotic factors, such as compaction, scalping, heat, localized dry spots and nutrient deficiencies, can cause symptoms that mimic those of diseases. The references mentioned earlier provide good clues as to how to distinguish between these causes and those of fungi or other pathogens.
Summer patch is a tough disease to control.
Common root diseases
Summer patch/necrotic ring spot - Summer patch and necrotic ring spot are two of the most damaging of all root diseases. Generally, necrotic ring spot occurs during the spring and fall, while summer patch symptoms appear in summer. Symptoms of these diseases are quite difficult to distinguish between, yet can be identified in the laboratory.
Affected turfs show 6 to 12-inch circular, semicircular or serpentine patches of light tan grass blades. A "pockmarked" or doughnut-shaped appearance often develops, with brown, matted turf plants, containing a tuft of apparently healthy turf in the center. This is sometimes referred to as the "frog eye effect." Nearby plants around the edge of the patches are commonly unthrifty due to slowed function of the roots, caused by either disease.
Spring dead spot - Injury from spring dead spot produces roundish patches of dead looking turf and can range from 6 inches to 2 feet in diameter. Spring dead spot is commonly only found on bermudagrass. In severe cases the spots will merge, creating larger, irregular patches in the turf. The affected turf appears brown to black in color, and in most cases the center of the patches will be slightly sunken. Spring dead spot is aptly named, as the infected turf is actually dead, requiring either replacement or encouragement to fill in from the edges. Because of its apparent high degree of tolerance to the spring dead spot pathogen, Poa annua is commonly the first plant to reestablish in the patches of dead turf.
Leaf spot/melting out - Even though it starts out as a leaf disease, the advanced stage of this malady is characterized by a necrosis of the crown and root system. The leaf spot pathogens, Bipolaris sorokiniana and Drechslera poae, are favored by cool, wet weather. Early symptoms of leaf spot are small, purple to black spots on the leaf blade. As the disease progresses, round to oval spots with buff-colored centers develop. In some cases they are outlined or surrounded by a dark brown margin. After several weeks of infection, the disease progresses to a "melting out" stage, where infected leaf sheaths turn a uniform dark chocolate brown, causing leaves to yellow and drop from the plant. From a distance, the stand takes on a thin, yellowish cast.
Common shoot diseases
Dollar spot - Symptoms produced by dollar spot are straw-colored, somewhat sunken patches; infected blades express tan leaf spots with reddish brown borders. Dollar spot is favored when there are warm days and cool nights that produce dew and high humidity in the turf canopy. It may occur any time from late spring to early autumn. More likely to become severe on nitrogen-deficient soils, individual dollar spot infections vary in size. On close-cut sports turf, they range from 1 inch to 1.5 inches, while infections in higher cut turf are usually 3 to 5 inches across. Individual leaf blades within the affected area develop with lesions up to 1-inch long, light tan with reddish brown margins. The lesions usually span the width of the leaf blade.
Brown patch - Symptoms include light brown grass blades usually not matted down, with irregular blotches of tan lesions with dark markings on the leaf blades. Patches of affected turf range from 6 inches to 2 feet in size. The lesions will not always go across the leaf blade as with dollar spot. Brown patch is often induced by heavy midsummer applications of nitrogen. The most influential factor in brown patch development is weather conditions of high heat and high humidity, especially when extended for more than 24 hours.
Stem and leaf rust - The severity of rust outbreaks varies from year to year, usually occurring from late summer to midfall following hot, dry periods when the growth rate of the turf has slowed. Turf injury becomes severe when poor growing conditions reduce turf vigor. Warm days and cool to moderate nighttime temperatures along with long morning dew periods or nighttime irrigation create optimal growing conditions for the fungi. In addition, turfs under lower fertility will typically have more rust.
Heavily rusted turfs appear yellow or orange when viewed from a distance. In severe infections, small clouds of rust spores can discolor shoes, mowing equipment and pant legs. Close examination of rusted leaf blades reveals the presence of the orange to brick red pustules, which rub off easily when touched. Each rust pustule produces a vast number of spores, each capable of infecting a grass blade. New infections can occur about every seven to 10 days. Infected turfs become weak and thin, predisposing them to winter injury and other abiotic stressors.
John Fech is an extension educator specializing in turf and ornamentals at the University of Nebraska-Lincoln. Dr. Loren Giesler is an Extension Plant Pathologist at the University of Nebraska-Lincoln.