How to Manage Pests

UC Pest Management Guidelines

Turfgrass

Rhizoctonia Blight (Brown Patch, Large Patch, Yellow Patch)

Pathogens: Rhizoctonia solani and R. cerealis

(Reviewed 9/09, updated 9/09, pesticides updated 12/16)

In this Guideline:


DESCRIPTION OF THE DISEASE

There are three types of Rhizoctonia blight: large patch, a blight of warm-season grasses that is caused by Rhizoctonia solani; brown patch, a blight of cool-season grasses that is also caused by R. solani; and yellow patch, a blight of annual and Kentucky bluegrass caused by R. cerealis. When weather conditions are not favorable for disease development, both species can survive as sclerotia in the thatch and soil or as mycelia in plants and debris.

Large patch on warm-season grasses appears as light green patches in fall. Infected areas may become bright yellow and then turn brown as the grass emerges from dormancy in spring. Spring symptoms can persist in cool, wet weather for an extended duration; bermudagrass can recover quickly as the weather warms, while other grasses, such as zoysiagrass, take many weeks to recover. There is often a soft, dark brown to purplish rot of the lower portion of the leaf sheaths that can develop into a reddish brownnecrosis of the leaf sheath and stem under dry conditions. In severe cases, plants will be affected by an extensive soft rot of the stems.

Brown patch affects cool-season grasses during periods of hot weather. On closely mowed turf, patches of blighted turf will often have a purplish edge or smoke ring appearance in the early morning hours. Initial patches may first appear purplish-green and turn brown as the disease progresses. On taller turf plantings, patches will appear as blighted turf that turns dull tan to brown. The fungus causes dull tan lesions on leaves that may develop a reddish brown margin. Plants killed by the fungus will often have a light brown color, and turn brittle, but will not have a wet, greasy appearance.

Yellow patch occurs primarily on annual bluegrass and Kentucky bluegrass in cool, moist weather. Symptoms include the development of yellow or tan-colored patches of turf. On leaves, there is a yellow to tan chlorosis that extends down from the leaf tips. Gray-tan lesions may develop on lower leaf portions and often on Kentucky bluegrass, some leaves may become reddish or reddish purple. In periods of extended cool, wet weather, affected leaves may become necrotic, but in many cases the main symptom is only a yellow chlorosis.

SUSCEPTIBLE TURFGRASSES

Large patch: Bermudagrass, zoysiagrass, St. Augustinegrass, kikuyugrass
Brown patch: bentgrasses, fescues, ryegrasses, bluegrasses
Yellow patch: annual bluegrass, Kentucky bluegrass, bermudagrass, perennial ryegrass, zoysiagrass, bentgrasses

CONDITIONS FAVORING DISEASE

Generally, Rhizoctonia diseases are more severe under conditions of poor drainage, high compaction, thick thatch layers, long periods of leaf wetness, low mowing heights, excessive mechanical damage, and high nitrogen fertilization.

Large patch develops in fall and spring when warm-season grasses are going into or coming out of dormancy.

Brown patch is common when temperatures are in the range of 75°to 95°F, with the optimal conditions for leaf colonization being temperatures of 85°to 90°F with high humidity or extended leaf wetness periods.

Yellow patch usually develops when air temperatures are from 50°to 65°F and there is high humidity or extended periods of leaf wetness. In many cases, the turf will recover when temperatures go above or below this range.

MANAGEMENT

Irrigation and leaf wetness management is an important part of controlling Rhizoctonia diseases. Fungicide applications can be necessary if leaf wetness and soil moisture cannot be adequately managed (for instance, as a result of rain or high humidity). Combine cultural management techniques with fungicide applications for the best management of the disease.

Cultural Control

Cultural practices that improve water and fertility management are useful in preventing the development of rhizoctonia blight. Reduce shading and improve soil aeration and water drainage. Irrigate in the pre-dawn or early morning hours to promote leaf drying. Irrigate only when needed to a depth of 4 to 6 inches. Remove dew from leaves by poling or light irrigation. Avoid nitrogen fertilization that results in a soft foliage growth. Maintain thatch at less than 0.5 inch.

Treatment Decisions

For areas where large patch and yellow patch are chronic, fall fungicide applications may be necessary; otherwise, make fungicide applications soon after the first symptoms of disease are seen. Some fungicides that are active against R. solani may not be specifically labeled for R. cerealis.

Common name Amount to use Ag Use
REI‡
NonAg Use
PHI‡
(Example trade name)   (hours) (days)

UPDATED: 12/16
Calculate impact of pesticide on air quality
Bee precaution pesticide ratings
When choosing a pesticide, consider its usefulness in an IPM program by reviewing the pesticide's properties, efficacy, application timing, and information relating to resistance management, honey bees (PDF), and environmental impact. Not all registered pesticides are listed. Always read the label of the product being used.
 
A. AZOXYSTROBIN
  (Heritage) 0.2–0.4 oz/1000 sq ft 4 Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
 
B. CHLOROTHALONIL
  (Daconil Action) Label rates 12 Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M5)
 
C. FLUDIOXONIL
  (Medallion) Label rates 12 Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Phenylpyrrole (12)
 
D. FLUTOLANIL
  (Prostar WG) Label rates 12 Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Carboxamide (7)
 
E. IPRODIONE
  (Chipco 26019) 3–4 fl oz/1000 sq ft. See label Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Dicarboximide (2)
 
F. MANCOZEB
  (Fore 80WP, Dithane M-45) 4 oz/1000 sq ft 24 Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Multi-site contact (M3)
  COMMENTS: Dithane M-45 registered for use on sod farms only.
 
G. MYCLOBUTANIL
  (Eagle 20EW) 1.2 fl oz/1000 sq ft 24 Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
  COMMENTS: Do not apply more than 7.2 oz/1000 sq ft/year.
 
H. PCNB
  (Turfcide 400) Label rates 12
  MODE-OF-ACTION GROUP NAME (NUMBER1): Aromatic hydrocarbon (14)
 
I. (PROPICONAZOLE
  Banner Maxx) 1–2 fl oz/1000 sq ft 12 Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
 
J. THIOPHANATE-METHYL
  (Fungo Flo) Label rates 12 Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Methyl benzimidazole (1)
 
K. TRIADIMEFON
  (Bayleton 50 Turf and Ornamental) Label rates 12 Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Demethylation inhibitor (3)
 
L. TRIFLOXYSTROBIN
  (Compass) Label rates 12 Until dry
  MODE-OF-ACTION GROUP NAME (NUMBER1): Quinone outside inhibitor (11)
 
1 Group numbers are assigned by the Fungicide Resistance Action Committee (FRAC) according to different modes of actions. Fungicides with a different group number are suitable to alternate in a resistance management program. In California, make no more than one application of fungicides with mode-of-action group numbers 1, 4, 9, 11, or 17 before rotating to a fungicide with a different mode-of-action group number; for fungicides with other group numbers, make no more than two consecutive applications before rotating to fungicide with a different mode-of-action group number.
Restricted entry interval (REI) is the number of hours (unless otherwise noted) from treatment until the treated area can be safely entered without protective clothing. Agricultural use applies to sod farms and commercial seed production.
Indicates use is not listed on label.

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Turfgrass
UC ANR Publication 3365-T

Diseases

A. Downer, UC Cooperative Extension, Ventura County
M. A. Harivandi, UC Cooperative Extension, Alameda County

Acknowledgment for contributions to Diseases:
F. Wong, Plant Pathology, UC Riverside
J. Hartin, UC Cooperative Extension, San Bernardino County
M. E. Grebus, Plant Pathology, UC Riverside

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