Gary Y. Gao
Barbara Bloetscher
Joseph F. Boggs
Pamela J. Bennett
Jane C. Martin
Joseph W. Rimelspach
John R. Street
Erik A. Draper
This article is compiled from reports of turf cultural and disease problems as well as cultural recommendations given in the weekly Buckeye Yard and Garden Line (BYGL) throughout the year of 2000.
Rhizoctonia blight became a serious problem by early July, especially on tall fescue in southern Ohio. Lesions on leaf blades initially appeared water-soaked and dark bluish-green, then withered, dried up, and turned brown. Moisture must be present on the leaves for the fungus to spread rapidly to healthy plants. Turf growing under high nitrogen fertility levels tends to be infected more readily.
Due to the cool, wet conditions during July in many areas of Ohio, crown rot anthracnose was seen on golf-course greens. This disease mostly affects annual bluegrass, but it can also infect creeping bentgrass. Poorly drained areas, where turf with dense thatch is regularly watered, favor development of this disease. Symptoms begin as reddish-brown patches, which progress to wilted dying turfgrass. Close inspection may reveal black acervuli (fruiting bodies) on the lower leaves and crown. These fruiting bodies are the main source of inoculum for further infection.
Although commonly found on the blades, where it is not lethal to the turf, anthracnose can spread throughout the plant. To manage this disease, minimize thatch accumulation and improve drainage, if applicable, and utilize preventive fungicides in areas conducive to this disease. Keep greens healthy and vigorous by applying a balanced fertilizer and watering only when needed.
Dollar spot began to be commonly reported by mid-June on Kentucky bluegrass/perennial ryegrass lawns due to warm, humid temperatures, cool evenings, and plentiful moisture. This disease can occur from late spring to late fall, once the air temperature reaches 60ºF. Rapid infection takes place when temperatures range between 70-80ºF. Unlike the distinct round, dollar-coin-sized patches on golf courses, patches on tall cut grass tend to be irregular and larger (2"-6").
Dollar spot on high-cut turfgrass can be distinguished from brown patch by the shape of the lesions on the leaf blades. Brown patch lesions have irregular, dark brown blotches on the blade, while dollar spot has horizontal bands across the leaves. A yellow border usually exists above and below the bands. Although fungicides are available, the treatments are expensive and most effective when used preventively. Also, it helps in managing these diseases to improve cultural techniques. With both diseases, frequent mowing and proper irrigation are key factors in limiting disease development.
Gray leaf spot, a "hot-weather disease," showed up on perennial ryegrass in southwestern Pennsylvania, northern Kentucky, and, in mid-August, in southern Ohio counties. This disease has occurred in Ohio from Cincinnati to Columbus. Tall fescue was reported as also being a host for this fungus in the southern United States; however, in Ohio the disease has only been found on perennial ryegrass.
Gray leaf spot usually affects intensively managed turf late in the year during hot, humid conditions. It can be difficult to distinguish from drought stress. As the blade dies from tip to crown, it twists, similar to a pig's tail. Infected turf usually dies. The fungus produces characteristic pear-shaped spores, which are visible under a microscope.
Fungicides labeled for gray leaf spot control include azoxystrobin (e.g., Heritage) and thiophanate-methyl (e.g., Fungo, Spectro 90 WG, Cleary's 3336). Other fungicides listed in a preventive program include trifloxystrobin (e.g., Compass 50 WG) and propiconazole (e.g., Banner MAXX) tank-mixed with chlorothalonil (e.g., Daconil Ultrex).
Heavy damage was reported on common Kentucky bluegrass due to leaf spot in May. This disease does not usually kill the plants; however, it was more severe this year with added mowing challenges (dense turf canopy) and cool, damp weather. Damage was heavy and resulted in severe thinning of the turf. In one plot, for instance, the turf was thinned by approximately 80%. Symptoms range from small oval spots on leaf blades, to fading out of the blades, to extensive rotting of the crowns and roots.
Common Kentucky bluegrass is extremely susceptible to leaf spot, which is found mainly in older, well-established stands. The most effective control is a combination of good cultural practices and using resistant cultivars of bluegrass. Where reseeding with an improved cultivar is not possible, use a fungicide preventively.
Red thread was rampant on many perennial ryegrass lawns in May. Red thread is especially prevalent in spring and fall on slow-growing, nitrogen-deficient turf. Circular or irregular shaped patches of infected grass become water-soaked and become tan in color. Patches can be widely scattered or coalesce to form large areas of infected turf.
Blades are the only part of the plant infected, and death proceeds from the leaf tip downward. When humidity is high, pink to pale red or orange fungal mycelial growth, called "red threads," may extend beyond the tip of the leaf blade. When red threads are present, the infected patches take on a reddish or tan cast that is easily detected. To manage the disease, water early in the day when necessary and maintain adequate and balanced fertility. Applications of fertilizer are helpful in reducing disease severity, but avoid excessive rates. Labeled fungicides may be applied if disease pressure is high.
The rust fungus was reported on residential and commercial lawns during the second week of July in Ohio. This foliar disease is recognized by a yellowing of turf blades, followed by reddish or orange-colored streaks on the bottom side of the leaves. It is most active on turf low in fertility and under drought stress, and spreads rapidly once temperatures stay at 85ºF with sunny skies, frequent showers, or heavy dew. Where turfgrasses have been infected in prior years, maintain a regular, balanced fertilizer regime, and water to avoid drought stress. A preventive fungicide application can be made for lawns with a history of heavy rust problems.
Stripe smut showed up in June in lawns with susceptible Kentucky bluegrass/perennial ryegrass cultivars. Striped smut develops in the spring and fall during periods of plentiful moisture and cool (50 - 70ºF) weather. The leaf blades appear streaked or striped with black dust. The "dust" is actually fungal spores which may be spread to other turf plants by wind and rain. When environmental conditions are favorable, the spores germinate, and the fungus forms mycelium which invades new leaf tissue, roots, and rhizomes. The mycelium grows systemically in the plant and remains there until the turf dies. Although fungicides are available, selection of disease-resistant cultivars and proper fertilization remain the best options to limit this disease.
Summer patch was diagnosed on annual bluegrass on golf courses during periods of hot, humid, wet weather, on frequently irrigated turf growing in poorly drained soil. Although the pathogen begins to infect the crowns and roots of annual bluegrass at 65ºF, symptoms of brown, depressed spots don't show up until temperatures reach 85-95ºF. Relieving stress, raising the mowing height, and maintaining a minimal thatch layer is crucial to avoid serious infections.
Yellow streaks, or irregular growth in patches of Kentucky bluegrass, were reported in home lawns, sod farms, and golf course roughs. Within these patches, newer leaf blades appeared light green or chlorotic. This unexplained phenomenon usually occurs during spring or summer when rainfall is abundant and the sky is overcast. It affects both common and improved Kentucky bluegrass under high- and low-fertilization regimes, and usually fades after two to four weeks.
The best long-term strategy against the invasion of annual weeds in the home lawn is the maintenance of dense healthy turfgrass. Some contributing factors to the formation and maintenance of dense lawns include proper species and cultivar selection, adequate fertilizations, proper watering, and maintaining proper mowing heights and mowing frequency. After our droughty conditions in 1999, some turfgrass lost the battle and needed to be reseeded in spring 2000. Those areas needed to be raked, graded, and any dead plants and thatch removed. Such areas should be replanted with grass(es) similar to what is already growing in the lawn.
Mowing frequency is extremely important in reducing the level of shock to the turf crowns. Proper mowing frequency results in short clippings that quickly disappear in the turf canopy and eliminates the need for removal. Cutting height and rate of growth, rather than fixed time intervals, determines the mowing frequency. No more than one-third of the total leaf surface should be removed at any one time. Removing more than one-third of the leaf surface results in an open, stemmy appearance of the lawn, weakens the grass plant, reduces or stops root growth, and leaves significant clipping debris on the lawn surface.
Core aerification in fall and spring was recommended for thatch management. Research has shown that this is the best approach to managing thatch when layers are 1/2" in depth or less. Lawns are aerified by pulling up cores of thatch and soil and depositing them on the lawn surface. Rainfall or irrigation break apart the soil cores, causing the soil to sift down onto the existing thatch layer. This addition to the thatch layer improves the environment for soil microbes, encouraging microbial activity to metabolize and break down thatch.
Soil cores should be 2" to 3" in length with a diameter of 1/2" to 3/4". At least 8 to 9 cores should be pulled per square foot. Depending on the aerifying machine used, more than one pass over the lawn may be required to achieve the desired number of holes.
Aerification can be performed in the spring (April or May) or in the fall (September or October) whenever the soil is cool and moist. Fall is the preferred time as soil moisture is adequate for tine penetration, temperatures are more conducive to lawn recovery, and root growth is favored. Unless excessive thatch layers are present, one aerification per year is generally sufficient.
A newly sodded lawn requires a lot of tender loving care. Proper watering is extremely critical for successful sod establishment. A sodded lawn should be irrigated to a depth of 6" immediately after transplanting. Subsequent irrigations on a daily, to every few days, basis will be required for two to three weeks to maintain adequate soil moisture during the initial root growth period. A sodded lawn should be mowed when the grass reaches a height of 3". An application of 0.5 to 1.0 pound of actual nitrogen and phosphorus per 1,000 square feet is highly recommended at the time of sodding for quicker establishment.
An application of 0.75 pound of actual nitrogen per 1,000 square feet in summer was recommended, especially for Kentucky bluegrass lawns, and lawns with low soil fertility. Select a fertilizer with a ratio of 3-1-2 to 5-1-2, and 30-50% of the nitrogen in slow release or controlled release form to avoid fertilizer burn.
To maintain a healthy lawn during the summer, water once or twice a week early in the morning, so that 1" of water is received. To determine how much water the lawn is getting, set a rain gauge in the lawn and track the time it takes to receive 1" of water. To maintain a lawn which has gone dormant, water so that the lawn receives 1" of water every 10-14 days. Raise the mowing height to allow more shade to the crowns and sharpen the mower blade if necessary. Maintain a balanced fertilizer program and avoid treating turfgrass with herbicides when temperatures rise above 80ºF, to avoid injuring the turfgrass or adjacent ornamental plants.
When renovating a lawn, it is advisable to determine which steps will be necessary before seeding.Thatch layers 1" or more should be removed before establishing a new lawn, and perennial weeds should be killed. Where zoysiagrass, Bermudagrass, quackgrass, or other persistent perennial grass weeds are present, multiple herbicide applications may be necessary before the grasses are dead.A soil test to determine nutrient levels and pH is also recommended.
Ideally, cool season turfgrass should be seeded in the fall when soil moisture is plentiful with daily temperatures between 60-75ºF and soil temperatures above 55ºF. This provides the perfect environment for turfgrass roots to develop without high demand for rapid leaf production.
Depending upon the soil moisture beneath the sod, percent organic material, and texture of the soil, it takes over three weeks for the roots to extend into the native soil. If the soil was not properly prepared before laying sod in the summer, the roots may take months to become established. Therefore, for best results when installing a new lawn, prepare the area for seeding or sodding, so that installation can be done properly in late August or September.
Seeding in central Ohio should be done by September 15 (one week earlier for northern Ohio), for optimal seedling germination. Although seeding can be done until October 1, depending on the timing of frosts and soil moisture, emergence and maturation of seedlings may not be as successful. Once the ground freezes, surface soil moisture is unavailable, and seedlings with a meager root system will dessicate and die. Starter fertilizer is essential for proper germination and development of seedling turfgrass, as seedling root systems have difficulty accessing nutrients, especially phosphorus, unless it is on the soil surface. Starter fertilizer NPK ratios should be 1-2-1 or 1-1-1. When possible, apply starter fertilizer again in five to six weeks.
1. Pound, W. E. and J. Street. 1991. Ohio State University Extension Bulletin 546. Lawn Establishment.
2. Street, J., W. E. Pound, D. J. Shetlar, C. C. Powell, W. W. Shane, S. K. White. 1991. Ohio State University Extension Bulletin 271. Your Lawn.
3. Boehm, M. J., W. E. Pound, J. W. Rimelspach, D. J. Shetlar, J. R. Street. 2000. Ohio State University Extension Bulletin L-187. Management of Turfgrass Pests.
4. Smiley, Richard, P. H. Dernoeden, B. B. Clarke. 1992. Second Edition. Compendium of Turfgrass Diseases. The American Phytopathological Society, St. Paul, Minnesota.