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Brown Patch. Knowledge Requirements. What are the best diagnostic signs and symptoms of brown patch? Is the pathogen a spore-former or a non-spore-former? How does the pathogen survive adverse conditions? How does the pathogen infect turfgrass plants?

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Presentation Transcript
slide2

Knowledge Requirements

  • What are the best diagnostic signs and symptoms of brown patch?
  • Is the pathogen a spore-former or a non-spore-former?
  • How does the pathogen survive adverse conditions?
  • How does the pathogen infect turfgrass plants?
  • What species of turfgrasses are susceptible?
  • How does mowing height affect the signs and symptoms of brown patch?
  • What effects do nutrients such as N, P & K have on the disease?
  • What environmental conditions are required for brown patch to develop?
  • 9. What species of turfgrass are resistant or immune to brown patch?
  • 10. What turf nutrients suppress brown patch?
  • 11. In what ways can the environment be manipulated to suppress
  • brown patch?
  • 12. Name a contact and penetrant fungicide that will control brown patch.
  • 13. During what season(s) are preventive applications of brown patch
  • fungicides applied in GA?
slide3

The disease once known as Brown Patch is now considered as 3 distinct diseases.

BROWN PATCH

Yellow Patch of

Cool Season Grasses

caused by:

Rhizoctonia cerealis

Brown Patch of

Cool Season Grasses

caused by:

Rhizoctonia solani

(strains AG 1 and

AG 2-2IIIB)

Rhizoctonia Large Patch of

Warm Season Grasses

caused by:

Rhizoctonia solani

(strain AG 2-2 LP)

slide4

First we will discuss the disease Brown Patch

BROWN PATCH

(a.k.a. Rhizoctonia blight)

caused by:

Rhizoctonia solani

(strains AG 1 and AG 2-2 IIIB)

Brown Patch affects only cool-season turfgrasses!!!

slide5

Rhizoctonia solani

(strains AG 1 and AG 2-2 IIIB)

  • Nonspore-forming fungus.
  • Survives as sclerotia or dormant mycelium
  • in thatch, soil or dead tissue.
  • Initial infection occurs on leaf sheaths and
  • leaves when night temps are >60°F and leaves
  • have been wet for more than 10 hrs.
slide6

BROWN PATCH

Susceptible grasses

-All cool season grasses are susceptible.

slide7

BROWN PATCH

Favorable environment

  • Night temperatures >60°F (16°C).
  • More than 10 hrs. of leaf wetness per day for
  • several days.
  • - Disease severe at soil pH<6 and on turf subjected
  • to drought stress.
slide8

Morning shade from

tree prevents turf

from drying = more

brown patch.

No morning shade.

Less brown patch.

slide9

BROWN PATCH SYMPTOMS

Symptoms of brown patch differ on grasses mowed

at low mowing heights (<1 inch) compared to

grasses mowed at heights >1 inch.

slide10

Among grasses usually mowed at > 1 inch

height, tall fescue is the most susceptible to

Rhizoctoniasolani in the southeast U.S.

slide11

Brown patch on tall fescue – Patches a few

inches to 2 or more feet in diameter.

Patches often coalesce

resulting in large blighted

areas

To diagnose Brown Patch,

look for lesions on leaves

at the edges of patches

slide12

Lesion caused by R. solani on fescue leaves

Hyphae growing between leaf blades

Lesions caused by R. solani on fescue leaves.

Lesions are gray to brown, irregular in shape,

and have a thin brown border. These lesions

are the best diagnostic symptom of brown

patch on tall fescue.

slide13

Brown patch

lesion

Dollar spot

lesion

The brown patch fungus and the dollar spot

fungus produce irregular foliar lesions with

thin brown borders. Note the difference

in color of the lesions.

slide15

Resistant Cultivars

Tall fescue cultivars differ in susceptibility to brown patch

slide16

Some cultivars of tall fescue that have exhibited

reduced brown patch and high turf quality in

the southeast U.S.

Reserve Anthem II

Crossfire II Safari

Apache II Scorpio

Coronado Gold Arid 3

Bonsai 2000 Mustang II

Helix Wolfpack

Tar Heel Jaguar 3

Dominion Genesis

slide17

Cultural Control (Environmental Manipulation)

leading to suppression of brown patch of tall fescue

slide18

Cultural practices that limit severity of brown

patch on tall fescue lawns

  • Maintain mowing height between 2 and 3 inches.
  • Lower mowing enhances disease.
  • 2. Avoid nitrogen applications from mid-May to
  • mid September. Summer N enhances disease.
  • 3. Decrease shade and increase air circulation. Long
  • periods of leaf wetness enhance disease.
  • 4. Avoid irrigation from approximately 2:00 pm
  • to midnight or later. Turfgrass foliage must be
  • allowed to dry before nightfall.
slide20

Although there are many fungicides that will

provide 2 to 4 weeks control of brown patch on

susceptible grasses, lawn care companies can’t

afford to return to most properties more frequently

than every 5 to 6 weeks.

There is no fungicide currently on the market that

will consistently provide 6 weeks control of brown

patch. However, two fungicides provide acceptable

control for 5 weeks…

slide21

Fungicides that provide >90% control of brown

patch when applied on a 5-week interval

Heritage 50WDG 0.2 or 0.4 oz./1000 sq.ft.

(azoxystrobin)

Prostar 70WP 3.0 oz./1000 sq.ft.

(flutolanil)

slide22

Fescue lawn in Georgia treated with

Heritage (azoxystrobin) at 5-wk-intervals

throughout the summer.

slide23

Next we will discuss Brown Patch on

turf that is usually mowed at a height

<1 inch.

Creeping bentgrass, perennial ryegrass and

annual bluegrass are the most susceptible

grasses in this category.

slide24

Brown Patch on a bentgrass

golf green.

Note dark “Smoke-Ring” caused by R. solani mycelium.

slide25

The smoke ring, which is visible in the a.m. when the turf is wet, is a good

diagnostic sign of brown patch on cool season grasses mowed at a

height of <1 inch.

Smoke-ring

slide26

Smoke-rings may

desiccate and disappear

when moisture dries

from leaf surface.

slide27

Occasionally, a smoke-ring may not form, even in the

morning. In this case, a sample taken from the edge of a

patch, moistened and placed in a plastic bag, may reveal dark

gray mycelium after 12-24 hrs of incubation.

slide28

Symptoms of brown patch may mimic

other diseases or disorders (eg. Take-All patch, dry spots). The ‘plastic bag trick’ can be used to make a positive diagnosis.

slide29

Management of Brown Patch

on Bentgrass

Resistant Species and Cultivars

  • Creeping bentgrass is more resistant than
  • colonial bentgrass.
  • Not much difference in resistance among quality
  • creeping bentgrass cultivars.
slide30

Management of Brown Patch

on Bentgrass

Cultural Control

  • Decrease shade and increase air circulation. Use
  • fans, trim or remove trees and schrubs.
  • Avoid irrigation in late afternoon and in evening
  • before midnight.
  • - Decrease N fertility on high risk areas.
slide31

Management of Brown Patch

on Bentgrass

Chemical Control

Contact fungicides – chlorothalonil, mancozeb,

thiram, polyoxin – 10 to 14 days control.

Localized penetrants – iprodione, vinclozolin,

trifloxystrobin, pyraclostrobin – 14 to 21 days control

Acropetal penetrants – azoxystrobin, flutolanil,

thiophanate-methyl, propiconazole, triadimefon,

fenarimol, tetraconazole, triticonazole – 21 to 28 days control

slide32

Management of Brown Patch

on Bentgrass

Chemical Control

Preventive fungicide applications for brown patch should begin

when night temperatures exceed 60°F for 3-4 consecutive nights.

In Georgia, this usually sometime during late May or early June.

slide33

Management of Brown Patch

on Bentgrass

Chemical Control

To date, no fungicide resistant strains of R. solani have been

detected on turf or other crops.

However, it is still a good idea to follow fungicide application

practices that will limit the probability of selecting fungicide

resistant strains. See Dollar Spot section for review of these

practices.