ACES Publications : CONTROLLING PYTHIUM BLIGHT ON OVERSEEDED&EST. TURF : ANR-0594

**ANR-594, Revised April 2004, Austin Hagan,** *Extension Plant Pathologist,* Professor, Entomology and Plant Pathology, Auburn University
Controlling Pythium Blight on Overseeded and Established Turf

Pythium blight, also known as cottony blight or grease spot, is a devastating disease in Alabama on overseeded and established stands of certain coolseason turfgrasses. Disease outbreaks occur most often on perennial ryegrass overseeded alone or in mixtures with bentgrass, fine fescue, and rough stalk bluegrass (Poa trivialis). Established bentgrass greens and tees are often badly damaged by Pythium blight. Occasionally, this disease has also been seen on turf-type tall fescue sod. Sporadic outbreaks have also been reported on intensively managed Bermudagrass.

Winter Pythium blight on bentgrass

Lush turf receiving large amounts of nitrogen fertilizers particularly those in low-lying or wet, poorly drained soils are the prime targets of the fungi causing Pythium blight. Pythium blight may occur on any susceptible turfgrass, regardless of age, when weather conditions favor disease.

Causal Fungi

Numerous fungi in the genus Pythium attack the foliage and roots of seedling and established turfgrasses. Species often cited as causing warm-season Pythium blight include P. aphanidermatum, P. myriotylum, and possibly P. ultimum. P. graminicola and P. torulosum have been associated with cool-season Pythium blight on bentgrass greens and tees. In the deep South, several other Pythium species are known to attack cool-season turfgrass seedlings.

Symptoms

Small, distinct, circular to irregular, grayish-green, watersoaked spots, usually several inches in diameter, develop. These spots often appear greasy or slimy, hence the name grease spot. Within several hours, the foliage of the blighted turf dries and turns light brown to tan. On higher-cut turfs, the damaged patches often reach a diameter of 1 foot and have a sunken appearance because of the collapse of the blighted foliage. Clusters of these blighted spots may merge, forming large irregular areas of dead turf. Wide streaks or unusual snake-like patterns may be seen where the fungi have been spread by flowing water or by maintenance equipment.

Severe Pythium blight development in late winter on an overseeded Poa trivilas fairway

The name cottony blight comes from the mass of cottony white fungal growth (hyphae) that is found in the early morning in the turf canopy, particularly on higher-cut turfs, when abundant moisture and high night temperatures favor pathogen activity. The cottony mass usually disintegrates by mid-morning as the leaves dry. Leaves and shoots of blighted turf, which are first dark-colored and watersoaked, later become dry and light brown. Straw-colored bands or spots occasionally may be seen when dry weather occurs, which does not favor rapid disease spread on the leaves and shoots of higher-cut turfs.

Cottony blight phase of winter Pythium blight on bentgrass

Yellowed, sparse seedling stands intermingled with patches of healthy dark-green turf are often an indication of Pythium seed rot or seedling damping-off. Discolored, water-soaked spots can often be seen on the shoots and leaves of affected seedlings. Diseased seedlings frequently turn yellow, wither, and die.

Disease Detection

Diagnosis of Pythium blight on the basis of symptoms alone can be a challenge, even for experienced turf managers. Symptoms can be confused with those of other turf diseases or disorders. Rapid-diagnostic kits employing enzyme-linked immunosorbent assay (ELISA) technology are expensive but very useful in the early diagnosis of Pythium blight. Foliage sampling should be done regularly to establish a background reading and to monitor Pythium activity in the target turf area. Preventive fungicide applications should be made when a strong positive reaction for Pythium fungi is obtained with the test kit. False positive test results may sometimes occur because the antibody system will not differentiate between non-disease-causing and disease-causing Pythium fungi. Rapid diagnostic kits are also available for the diagnosis of dollar spot and Rhizoctonia brown patch.

Turf samples may also be sent to the Plant Diagnostic Laboratory for diagnosis. See Extension publication ANR-450, "Plant Diagnostic Laboratory," for instructions on collecting and shipping samples.

Disease Cycle

The fungi associated with Pythium blight are common inhabitants of the soil and thatch of all turfs. These fungi survive as resting spores in dead and decaying leaves, shoots, and stems. Germinating resting spores may produce hyphal threads that directly invade healthy plants or release numerous mobile spores capable of moving in free water to their hosts. Running water can disperse these spores over a wide area. When temperature and moisture conditions are favorable, hyphal threads of the Pythium fungi grow rapidly through the turf canopy.

Specific temperature and moisture requirements must be met for the development of Pythium blight. Relative humidity must be 90 percent or more over at least a continuous 14-hour period for infection and colonization of host tissues. In general, the wetter the weather, the more likely that warm and cool-season Pythium blight will occur. Excess watering, particularly in the early evening, may extend the duration of leaf wetness long enough for significant pathogen activity.

Temperatures over much of the year in Alabama favor warm-season Pythium blight on cool-season turfgrasses. Specific temperature requirements for disease development are (1) maximum daily temperature of 86 degrees F or more and (2) minimum temperature of no less than 68 degrees F over a 24-hour period. Pythium blight severity increases sharply as day and night temperatures rise above the minimum for disease development. Several successive warm nights greatly increase the chances of a disease outbreak. Cool-season Pythium blight, which occurs at temperatures of 55 to 65 degrees F, has been seen in late fall to early spring on the bentgrass greens on Alabama golf courses. Pythium seed rot and seedling disease often occur when weather conditions do not favor rapid seed germination and seedling growth.

Disease Control

CULTURAL PRACTICES

Cultural practices should be used to maintain an environment that does not encourage the survival and growth of Pythium sp. Moisture is among the most critical factors influencing disease development.

Greens, tees, and other disease-prone turf should have good surface and subsurface drainage.
Water between 2 a.m. and 6 a.m. or at mid-day because watering in the early evening may increase the risk of disease by greatly lengthening the time the foliage remains wet.
Increasing air circulation by selective placement or pruning of trees and shrubs will speed evaporation of water from the turf canopy, thereby reducing the risk of disease.
Avoid overusing nitrogen fertilizers.
Maintain balanced soil fertility by following soil test recommendations.
Control thatch, an important survival site of Pythium fungi, with regular topdressing and core aerification or verticutting. When you see symptoms, delay mowing until the turf canopy has thoroughly dried and collect all clippings.
Delay overseeding warm-season turfgrasses until night temperatures have cooled.
Use only quality seed treated with a Pythium fungicide seed dressing such as etridiazole (Koban) or preferably mefonoxam (Apron) and use the correct rate.

Preventive fungicide treatment programs are required to protect turf overseeded with cool-season turfgrasses or established bentgrass greens and tees from Pythium blight. Systemic fungicides such as mefonoxam (Subdue), propamocarb (Banol), or fosetyl- Al (Aliette) will give up to 3 weeks of protection from this disease. When weather patterns favor rapid disease development, intervals between applications should be reduced to as few as 7 days and application rates increased. Information on application rates and treatment intervals is summarized in Table 1 and in Extension publication ANR-500-B, "Alabama Pesticide Handbook, Volume 2 ." The manufacturer of mefonoxam recommends that no more than three applications of this fungicide be made annually.

Table 1. Fungicides Recommended for Control of Pythium Blight on Turfgrass

Fungicide	Amount to use per 1,000 square feet	Comments
azoxystrobin Heritage 50W	0.4 oz.	Apply at 14- to 28-day intervals when conditions favor disease. Use highest rate at the shortest interval when disease is present. Do not make more than 6 applications or 3.7 oz. per 1,000 square feet .
chloroneb Fungicide V 6G Teremec SP 65W	3 to 5.9 lb. 4 oz.	Apply at 5- to 10-day intervals when conditions favor disease and at the highest rate at the shortest interval when disease is present. See label for suggested spreader settings for Fungicide V.
chloroneb + thiophanate-methyl Fungicide IX	1.9 to 5.8 lb.	Apply to wet foliage at 5- to 7-day intervals when conditions favor disease. Increase rate when disease is present. See label for suggested spreader settings.

etridiazole Koban 1.3 G Koban 30W Terrazole 35W	3 lb.	ESTABLISHED TURF: Apply with spreader at 5- to 10-day intervals and at the shortest interval when disease is present.
	8 lb.	NEWLY SEEDED TURF: Apply over newly seeded areas and lightly topdress. Repeat 5 to 7 days later with recommended fungicide.
	2 to 4.5 oz.	ESTABLISHED TURF: Apply at 5- to 10-day intervals in 5 gallons of water per 1,000 square feet when conditions favor disease and at the shortest interval when disease is present.
	7 to 9 oz.	NEWLY SEEDED TURF: Apply at 5- to 10-day intervals in 5 gallons of water per 1,000 square feet when conditions favor disease and at the shortest interval when disease is present. Irrigate immediately. For use on overseeded cool-season turfgrasses such as perennial ryegrass or Poa trivilas.
	4 to 8 oz.	ESTABLISHED TURF: Apply in 5 gallons of water per 1,000 square feet. Start applications at first sign of disease and repeat every 5 to 10 days when conditions favor disease.
fosetyl-AL Aliette Signature Aliette T/O Prodigy DG	4 to 8 oz. 4 to 8 oz. 4 to 8 oz.	Apply when conditions favor disease at 14- to 21-day intervals in 1 to 5 gallons of water per 1,000 square feet. Use higher rate and/or shorter intervals when disease is present. DO NOT mow or water until residues dry on foliage. Summer Stress Complex: Apply tank mix of Aliette with Chipco GT, Daconil Ultrex, or Dithane/Fore WP at 14-day intervals. Aliette formulations are not compatible with flowable formulations of Daconil Weather Stik or Fore Flowable.

metalaxyl* Pythium Control	1.3 to 2.6 lb.	ESTABLISHED TURF: Apply with a spreader at 10- to 21-day intervals. Use higher rate at shorter interval when disease is severe. See label for spreader settings.
metalaxyl* Pythium Control	1.3 to 2.6 lb.	NEWLY SEEDED TURF: Apply immediately after seeding and repeat when conditions favor disease.
mefonoxam* Subdue MAXX	0.5 to 1.0 fl. oz.	ESTABLISHED TURF: Apply at 10- to 21-day intervals in 3 to 5 gallons of water per 1,000 square feet when conditions favor disease. Use higher rate at shorter interval when disease is severe. Tank mix with Fore/Dithane T/O at 8 ounces per 1,000 square feet to improve performance. See label for mixing instructions.
	0.5 to 1.0 fl. oz.	NEWLY SEEDED TURF: Apply in 5 to 10 gallons of water per 1,000 square feet immediately after seeding and then irrigate with 0.25 inches of water. Repeat at 7- to 14-days if conditions remain favorable for disease. Tank mix with Fore/Dithane T/O at 8 ounces per 1,000 square feet to improve performance. See label for mixing instructions.

mefonoxam + triadimefon Fluid Fungicide II	0.7 to 1.4 fl. oz.	ESTABLISHED TURF: Apply at 10-day intervals in 4 to 7 gallons of water per 1,000 square feet when conditions favor disease. When disease is present, used higher rate at shorter interval.
mefonoxam + triadimefon Fluid Fungicide II	0.7 to 1.4 fl. oz.	NEWLY SEEDED TURF: Apply low rate immediately after seeding and with 0.25 inches of water. Repeat at 5 to 7 day intervals when conditions remain favorable for disease.
Mono-and di-potassium salts of phosphorous acid Allude	5 to 10 fl. oz.	ESTABLISHED AND NEWLY SEEDED TURF: Apply in 1 to 5 gallons of water per 1000 square feet until foliage is thoroughly wet. Repeat applications at 1 to 2 weeks as need to control disease. Do not irrigate or mow treated areas until spray has completely dried. Tank-mix with Protect T/O at 4 to 8 oz. per 1,000 square feet for control of Summer Stress Complex on bentgrass greens.
propamocarb Banol 66.5F	1.3 to 4 fl. oz.	ESTABLISHED TURF: Apply in 2 to 5 gallons of water per 1,000 square feet as a preventative treatment when conditions favor disease. Repeat applications at 7- to 21-day intervals according to disease pressure. When disease is present, apply highest rate at the shortest interval.
*To reduce the risk of resistance, make no more than 3 applications of metalaxyl or mefonoxam fungicides per season and alternate these fungicides with another Pythium fungicide such as Aliette or Banol.

Fungicide And Formulation			Amount To Use Per 100 lb. Seed	Comments

*Fungicide Seed Dressings*
	metalaxyl			Apply as water slurry with commercial seed treatment equipment.
		APRON FL	1.5 fl. oz.
		APRON 25W	2 - 4 oz.

		APRON DRY SEED PROTECTION 12.5 W		Apply just prior to planting. Thoroughly mix seed product for maximum seed coverage.
		APRON DRY SEED PROTECTION 12.5 W	4 - 8 oz.
	etridiozole
		KOBAN 30W	4 1/2 - 7 oz.	Add to seed in commercial seed treatment equipment and mix until through coverage is obtained.

* Precaution: To reduce risk of resistance, make no more than 3 applications of mefonoxam- or metalaxyl-containing fungicides per season and alternate mefonoxam or metalaxyl with another systemic Pythium fungicide.

On disease-prone overseeded turfs, an application of one of the above fungicides immediately after seeding should help prevent stand loss due to Pythiumincited seed rot and seedling disease. One to two additional fungicide applications at recommended treatment intervals and rate are suggested after seeding to guard against further outbreaks of Pythium blight until the onset of cool early winter. If Pythium blight should appear, one to two applications of the full rate of etridiazole (Koban, Terrazole) or chloroneb (Teremec, ProTurf Fungicide 11) at 3- to 5-day intervals should stop further disease spread. When the weather forecast during the winter and early spring fits the temperature and moisture profile for Pythium blight development, make one or more applications of fosetyl-Al or propamocarb.

In the deep South, bentgrass greens and tees require nearly year-round Pythium blight protection. From early spring through late fall, alternate two systemic fungicides such as mefonoxam, metalaxyl, fosetyl-Al, or propamocarb at 3-week intervals. Again, shorten the spray interval to as few as 10 days and increase application rates when weather conditions favor disease. Use one or two applications of the full rate of etridiazole at 3- to 5-day intervals to suppress any Pythium blight outbreaks. Limited information on chemical control of cool-season Pythium blight is available. Fosetyl-Al, mefonoxam, and propamocarb fungicides are the best bets for the control of cool-season Pythium blight on bentgrass. Metalaxyl, which has little activity against the Pythium sp. known to cause cool-season Pythium blight, should not be used from late fall to early spring. The performance of propamocarb and metalaxyl is often improved when they are tank-mixed with the full label rate of mancozeb (Fore, Dithane M-45, Dithane F-45, and Manzate 200).

Forecasting Fungicide Applications

Outbreaks of warm-season Pythium blight on bentgrass have been forecast with some success by looking at weather conditions. Disease is likely on days when the following conditions occur:

Fourteen continuous hours of at least 90 percent relative humidity
Maximum daily temperatures of at least 86 degrees F
Minimum temperatures of no less than 68 degrees F

A day for forecasting purposes is from noon one day to noon the following day. Forecasting Pythium blight outbreaks using weather parameters may be useful for scheduling fungicide applications to bentgrass and overseeded turfs in the early spring and late fall. Weather conditions from late spring to early fall are usually favorable for disease development.

Fungicide Resistance

In recent years, failures to control Pythium blight on bentgrass with the systemic fungicide metalaxyl have been blamed on fungicide resistance or tolerance. These failures have occurred on golf courses where metalaxyl was used exclusively for several years as a preventive treatment for Pythium blight. Mefonoxam or metalaxyl resistance has not been found in Alabama. However, the risk of resistance-related control failure is rather high because of the nearly season long fungicide treatment program required to maintain healthy bentgrass and the widespread use of this fungicide by golf course superintendents.

Fosetyl-Al and propamocarb are also systemic fungicides but the risk of control failures because of resistance with these fungicides is lower than with mefonoxam and metalaxyl. Pythium spp. have not developed resistance to contact, non-systemic fungicides such as chloroneb, mancozeb, and etridiazole after years of widespread use. These fungicides are considered very low risks for resistance-related control failures.

Reduce disease pressure by using recommended cultural practices as much as possible. Fungicides should be used only when necessary. Use enough fungicide to maintain effective disease control but do not exceed labeled application rates. Alternating mefonoxam or metalaxyl applications with a second systemic fungicide having a different mode of action such as propamocarb or fosetyl-Al greatly reduces the risk of resistance developing to either fungicide. When alternating two fungicides, both must be used at full label rate.
Limit the use of high-risk fungicides like mefonoxam or metalaxyl to one or two critical situations. In addition, tank mix combinations of high and low risk fungicides such as metalaxyl + macozeb have been used with some success to slow the development of resistance strains of the target fungi.

Use pesticides only according to the directions on the label. Follow all directions, precautions, and restrictions that are listed. Do not use pesticides on plants that are not listed on the label.

The pesticide rates in this publication are recommended only if they are registered with the Environmental Protection Agency or the Alabama Department of Agriculture and Industries. If a registration is changed or canceled, the rate listed here is no longer recommended. Before you apply any pesticide, check with your county Extension agent for the latest information.

Trade names are used only to give specific information. The Alabama Cooperative Extension Service does not endorse or guarantee any product and does not recommend one product instead of another that might be similar.

For more information, contact your county Extension office. Look in your telephone directory under your county's name to find the number.