Ask the expert: Understand large patch

Derek Settle, Ph.D., is part of the Bayer Green Solutions Team.

Fall is about to begin: August has ended and another summer season is almost behind us. Fall, one of the shoulders of a growing season, is about to begin and is a time when a golf course superintendent’s thoughts center on to-do lists. It is a cooler, kinder environment – or is it really? For those who manage zoysiagrass fairways and tees, one disease in particular will begin anew as temperatures begin to cool in August and September. Simply called large patch, this disease of warm season turf is caused by the soilborne fungus Rhizoctonia solani AG 2-2 LP. Large patch is particularly troublesome on zoysiagrass. The common name refers to the disease’s ability to damage large areas, and circular patches can be found, on occasion, measuring 20 feet or more in diameter. 

Large patch likes it cool and wet: Large patch is active in both fall and spring as long as temperatures remain between 50-86 degrees F. The after-effect can be severely thinned turf areas that, in addition to having an objectionable look, are more prone to encroachment by weeds. Across a fairway, the distribution of the disease isn’t exactly a random pattern. This is because large patch development is exacerbated by soils that remain saturated for extended periods of time. Therefore, expect to see low or compacted areas with more symptoms/signs of large patch.

Warm season turf is vulnerable both fall and spring: Large patch attacks slowly growing, warm season turf that is semi-dormant, or turf that is going into or emerging from dormancy. Large patch symptoms can persist for a long time, especially if the following spring is cool. Diseased zoysiagrass may not recover completely until summer. In the transition zone, the disease is most active in the fall and spring. In warmer climates like Florida, the disease can be continuously active fall through spring because cool nighttime temperatures (50s) without freezing can persist for long periods. In the South during wet years, significant damage occurs both fall and spring. During a cool summer, large patch symptom development can begin as early as the first week of August.

Large patch symptoms: Warm season turf will often appear yellow to orange in color. The outer edge of the expanding patch is often an even brighter color and is referred to as the “orange firing” symptom in zoysiagrass. On an individual plant, the actual site of infection is actually located lower in the canopy on the leaf sheath near the stem and crown region. 

Host range: R. solani AG 2-2 LP can infect a number of warm-season turf species including bermudagrass, buffalograss, centipedegrass, kikuyugrass, seashore paspalum, St. Augustine grass and zoysiagrass. Therefore, the older common name “zoysia patch” is not an adequate description of the disease, and today the more general name “large patch” is used.

Correct timing is important: Late summer and fall is the best time to prevent large patch with fungicides. Over the years, large patch research has indicated that the first fungicide application in late summer and fall is most important because good to excellent control can occur if it is timed correctly.  Bayer actually has developed and guaranteed programs that begin in the fall for control of large patch on golf courses. The fungicides recommended in the Bayer program include Prostar 70WG and Mirage StressGard. Mirage StressGard is Bayer’s newest broad-spectrum fungicide and can provide control of large patch similar to Prostar 70WG.<sup>1, 2

1</sup>Based on Bayer’s most current large patch studies with university cooperators in 2013-14.  ²See product labels for complete information and additional use instructions. Always read and follow label instructions carefully.

Prevention: Cultural practices can reduce the development of large patch disease. 

Cultural strategies to help combat large patch
•    Improve drainage – Install drainage to alleviate wet fairway areas.
•    In fall, avoid over-irrigation – Too much irrigation during cool weather can trigger large patch outbreaks.
•    In fall, restrict nitrogen fertility – Excessive nitrogen in the fall has been shown to increase large patch. 
•    In fall, plan for next year’s aerification – Schedule aerification of heavily trafficked, compacted areas in summer when warm season turf is actively growing.

Fungicide strategies to control large patch
•    Correct fall application timing – Time the first fall application when the average thatch temperature is 70 degrees F or when the average soil temperature at a 2-inch depth is 72-75 degrees F.
A second fall application is recommended 28 days later to extend protection through cool, wet weather.
•    Spring fungicide application – A third fungicide application in the spring should take place when turf green-up reaches 50 percent, and not any later.
•    Correct application spray volue – Apply fungicides at a spray volume of 2 gallons per 1,000 square feet to ensure penetration to crowns and stolons (at lower spray volumes a light watering-in, not greater than ¼ inch, is necessary).

Reference
http://www.backedbybayer.com/system/white_paper/asset_file/58/BPG_Solutions_LargePatch_WARM.pdf