Gary Y. Gao, Joseph F. Boggs, Pamela J. Bennett, Jane C. Martin, David E. Dyke, Joseph W. Rimelspach, Barbara Bloetscher, John R. Street, William E. Pound, and James A. Chatfield
This article is compiled from reports of turf cultural and disease problems as well as recommendations in the weekly Buckeye Yard and Garden Line (BYGL) throughout the year of 1998. Common turf diseases in 1998 included pink snow mold, leaf spot, red thread, necrotic ring spot, powdery mildew, brown patch, Pythium blight, fairy rings, dollar spot, rust, and gray leaf spot. Many turf problems were related to unusual weather conditions in 1998. Turfgrass seed head production, turf quality, summer turf management, lawn mowing, and turf reseeding are also discussed.
Lawn mowing is one of the most important turf management practices. Mowing turfgrass too short in early spring is more harmful to root growth than mowing short at any other time because the leaves return photosynthates (food) to the roots. Leaf blades that are continuously mowed too short result in short, meager roots. The cool season grasses form most of their roots in spring and again in fall and late fall. Mowing turfgrass too short stresses the entire plant and reduces root development significantly. Mow frequently and never remove more than one third of top growth at any one time.
Extended cool, wet weather in early spring favored many turfgrass diseases including snow mold, leaf spot, and red thread. BYGLers stressed that proper mowing was one of the main keys for disease prevention. Fungicide recommendations for these diseases are found in Ohio State University Extension Bulletin L-187, 1998 Management of Turfgrass Pests.
The cool wet weather in mid-May and resultant infrequent mowing prompted heavy seed head production in turfgrass, especially Kentucky bluegrass and perennial ryegrass. Tough stems from seed heads did not cut well, significantly reducing mowing quality. Much variation in seed head production was evident among Kentucky bluegrass cultivars.
Red thread continued through early June due to the cooler temperatures and damp conditions. However, as the moisture dropped, severely infected leaves browned and died, leaving tan brown dead spots. This disease produces irregular patches of blighted or browned grass ranging in size from two inches to three feet in diameter. Water-soaked spots appear first, followed by general drying out of the infected tissue. The tissue fades to a tan color. Under damp con-ditions, leaves may be covered with a pink, gelatinous, thread-like growth of fungus. This growth may extend from the leaf tips to nearby plants.
Control measures include a good fertility program, mowing a bit shorter to promote rapid drying of affected areas, and a fungicide program if the problem is severe. At times the stressed turf becomes susceptible to summer diseases.
Hot days came in mid- to late May. BYGL readers were reminded to start implementing summer turf-management practices. Mowing height should be raised to 2-3/4 to 3 inches and mowing frequency decreased to every seven to eight days as turf growth rates lessens. To minimize stress on the turfgrass and the mower operator, mow during morning or late afternoon hours instead of in the heat of the afternoon. Readers were also referred to Ohio State University Extension Fact Sheet HYG-4029-96, Managing Turfgrass under Drought Conditions for more turf management tips.
Lawn quality continued to decline in early June 1998. In many areas, dry-weather injury appeared as localized browning on slopes and under trees and as streaking from mower injury. Grass on compacted, heavily thatched, and poor soils browned. In some parts of Ohio, lawns became dormant.
Rhizoctonia blight became a serious problem in early July, especially on tall fescue. Blades first appeared water-soaked and dark bluish-green. Then the leaves withered and turned brown. Lesions were evident along the leaf margins. This disease requires the presence of moisture on the leaves for the fungus to spread to healthy plants. Turf growing under high nitrogen is more susceptible.
Mowing height had a significant effect on brown patch on tall fescue this year. Recent observations at the Clark County Regional Turf Education Plots revealed significantly more brown patch (Rhizoctonia solani) in the high-cut (3") versus the low-cut (1.5") tall fescue plots.
In the higher-cut plots, the canopy stayed wet much longer, providing the perfect environment for the fungus to spread, resulting in extensive damage to the leaves and large brown patches in the turf. In the shorter-cut plot, the canopy dried rapidly, which inhibited fungal growth and subsequent turf damage. However, during dry periods, the high cut is recommended.
Pythium was active in early July on golf courses and on newly seeded, heavily watered lawns. Pythium requires day-time temperatures of 90°F and night-time temperatures of 70°F for symptoms to appear. Since Pythium can kill turf, controls are a must to prevent further damage.
Pythium blight, brown patch, and dollar spot can look similar to both the untrained or trained eye during early morning hours when mycelium are present. Often, suspected cases of Pythium blight were mis-diagnosed. Brown patch and dollar spot usually do not kill turf, although they damage leaf tissue and reduce quality; therefore, it is not always necessary to apply expensive fungicides to control these two diseases. When in doubt, send samples to Ohio State University's C. Wayne Ellett Plant and Pest Diagnostic Clinic (PPDC) for diagnosis.
Fairy rings became evident in a few central Ohio lawns in early July. This curious phenomenon can be produced by 50 or more species of soil-inhabiting fungi. These fungi grow on decaying organic matter and are often associated with thatchy lawns or areas where trees have been removed.
Fairy rings can take on different patterns, including mushrooms that appear in circles or arcs, as dark green rings, or without mushrooms with a circular area of dead grass. The mushrooms are the fruiting structures of the fungi. The diameter of a fairy ring may vary from three to four feet up to 200 feet, and ring width may range from only a few inches up to two feet in width. Each season, fairy rings may grow a few inches to several feet in diameter. Sometimes fairy rings disappear for a year or more and then reappear.
The darker green ring of grass is due to increased nitrogen that becomes available as the fungus breaks down organic matter in the soil. Brown or thin grass may develop inside the darker green ring; this may be related to drought stress caused by dense growth of underground fungal structures.
Little can be done to control fairy rings, although symptoms can be suppressed. Fertilizing lightly may reduce the contrast between the lawn and darker green ring, as will irrigating with large quantities of water. Total "eradication" includes soil excavation and replacement, killing the grass in the ringed area, and then reseeding. A few fungicides are labeled for fairy ring control, but suppression may only be temporary.
In early August, dollar spot was quite heavy in Kentucky bluegrass lawns due to the lack of growth from drought. Although this disease affects bluegrass and tall fescue, it is generally more serious on bentgrass. The disease appears as round, brown, or bleached spots the size of a silver dollar or somewhat larger. Infected grass blades are often a straw-colored tan with reddish- brown margins.
If dollar spot is heavy, three management techniques will help:
Dollar spot does not kill the plants, and the lawn will recover under normal
growing conditions. A more long-term solution would be to use resistant cultivars
during turf installation or renovation. A listing of resistant bluegrass
cultivars can be found by visiting the National Turfgrass Evaluation Program
website at:
http://hort.unl.edu/ntep/tables.html
If a more immediate response is desired, homeowners can use fungicides containing chlorothalonil. Golf-course managers can find a list of products labeled for commercial use by referring to OSU Extension Bulletin L-187. An important note -- fungicidal applications must be frequent in order to suppress this disease successfully.
The year of 1998 was a banner year for rust, especially during dry periods. This year, rust was reported in southwestern Ohio as early as May. In general, the same recommendations for managing dollar spot will also suppress rust. However, fungicides available to homeowners contain chlorothalonil, and this usually provides poor control of rust. Triadimefon (e.g., Bayleton) and propiconi-zol (e.g., Banner) are recommended to commercial applicators, if chemical control is necessary.
Gray leaf spot, a relatively new disease in Ohio, was reported in mid-August. The rapid wilting, collapse, and death of ryegrass in lawns or fairways may indicate gray leaf spot. It commonly develops in late August under hot, humid conditions. The first confirmed sample of this disease (from northern Kentucky, across the river from Cincinnati) was received August 18 in the C. Wayne Ellet Plant and Pest Diagnostic Clinic. Turf samples suspected of being infected with gray leaf spot should be sent to the PPDC.
Turf samples with necrotic ring spot (NRS) were identified in the PPDC in mid-August. NRS symptoms appear when wet weather is followed by hot, dry periods. The fungus grows during the cool, wet spring months but does not show until the stressed turf suffers from depleted roots and higher water demands. It appears first as small, scattered, circular, light-green to straw-colored patches on Kentucky bluegrass (but also affects annual bluegrass and red fescue).
As the disease progresses, the patches become sunken or crater-like and appear as rings or arcs of dead turf, with a green center of recovering turf, called a frog-eye. To diagnose NRS, examine root and crown tissues. Darkly pigmented (black or brown) fungal threads appear on the surface of the root when viewed through a microscope. Frog-eye symptoms and dark runner hyphae are diagnostic characteristics.
Where frequent irrigation was possible, late August was a good time to begin reseeding home lawns to repair the areas with dead grass or spots infested with perennial weeds such as bentgrass, rough bluegrass, or nimblewill. However, brown turf at this time did not necessarily mean dead turf. Many home lawns had simply gone dormant due to water stress or insect damage.
When renovating areas infested with grass weeds such as bentgrass, rough bluegrass, or nimblewill, it is very important to completely kill the weed before reseeding. Water weeds first and make sure they have ample foliage for herbicide absorption. It is not effective to apply glyphosate (i.e., Roundup) to brown grasses or grasses with very limited leaf surface area. In addition, wait for five to seven days for the herbicide to translocate to the roots for total kill of weed roots. Otherwise, reseeded areas will still look poor since some of the perennial weeds will grow again along with desirable turfgrass.
Refer to Ohio State University Extension Fact Sheet HYG-40-1192 for information on Turfgrass Species Selection; HYG-4027-91, Turfgrass Cultivar Selection; and OSU Extension Bulletin 546, Lawn Establishment.
In addition, the 1997 progress report of the USDA National Turfgrass Evaluation Program was made available in August. It listed the rankings of top-named cultivars, based on quality ratings, for the four prominent turfgrasses in Ohio. This list is available through local Ohio State University Extension offices.
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, and S. K. White. 1991. Ohio State University Extension Bulletin 271, Your Lawn.
3. W. E. Pound, J. Rimelspach, J. Street, D. J. Shetlar. 1998. Ohio State University Extension Bulletin L-187, Management of Turfgrass Pests.