Large Patch: A New Turf Disease
In the USA and parts of Asia a specific form of Rhizoctonia solani known as AG 2-2 LP causes a disease called Large Patch in a range of warm season turfgrasses including Couchgrass, Zoysia and Kikuyu. Dedicate Forte Stressgard® has recently been registered for the control of this disease.
Over the last few years, a patch disease has developed on Kikuyu turf. Disease development tended to occur between autumn and spring. Symptoms were very large patches of affected turf. Examination of samples found the roots to be severely infected with Rhizoctonia solani. This pathogen is commonly referred to as brown patch and is known to cause disease on a range of turfgrass species.
In the USA and parts of Asia a specific form of Rhizoctonia solani known as AG 2-2 LP causes a disease called Large Patch in a range of warm season turfgrasses including Couchgrass, Zoysia and Kikuyu. It attacks slowly growing, warm season turfgrass in cool, wet weather, and is most common on turfgrass that is semi-dormant or turfgrass that is going into or emerging from dormancy. In temperate climates the disease is most active in the autumn and spring, whereas in tropical climates the disease can be continuously active autumn through spring. Damage can persist through cool, wet conditions and often lasts until warmer spring or summer conditions allow for recovery and active regrowth of warm season turfgrass.
Rhizoctonia from samples collected in South Australia have undergone DNA sequencing and confirmed the pathogen is the AG 2-2 LP variant. Samples from Western Australia are still undergoing testing, but it seems that these are also the large patch variant.
R. solani AG 2-2 LP is active at 10-30oC with optimal infection occurring at 21-27oC. Large patch symptoms vary with patches ranging in diameter from 30cm to over 6 metres. Patch interior becomes sunken, and injured turf appears thin with a tan, yellow or orange colour. A useful diagnostic feature in the field is a brilliant “orange firing” of the expanding outer ring, which indicates active infection. Damage by large patch can be long-lasting because infection occurs when warm-season turf growth is slow. In summer, turf recovers because the disease is not active at warm temperatures (> 30oC).
Cultural practices are the first step in reducing large patch.
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Improve drainage whenever possible, as saturated soil conditions exacerbate large patch
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Regular aeration in summer will reduce compaction and risk of having water-logged soils
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Minimize late-summer/autumn nitrogen applications
Control with fungicides:
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DMI fungicides – The preferred mode of action for soil-borne pathogens like this. Dedicate® Forte Stressgard® has recently been registered for the control of this disease.
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Applications should begin in the autumn as the soil temperature drops to 22-24°C, with a second application 28 days later. Application can be made in the spring when turf begins active growth.
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Apply in a water rate up to 1600L/Ha. Follow with irrigation to wash into the root zone.
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Adelaide |
Perth |
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Orange "firing" around edge of patch. |
Untreated (L) vs Treated with Dedicate® Forte® (R). |
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