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Large Patch. Knowledge Requirements. What are the best diagnostic signs and symptoms of large 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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slide2

Knowledge Requirements

  • What are the best diagnostic signs and symptoms of large 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?
  • What effects do nutrients such as N, P & K have on the disease?
  • What environmental conditions are required for large patch to develop?
  • 8. What species of turfgrass are resistant or immune to large patch?
  • 9. What turf nutrients suppress large patch?
  • 10. In what ways can the environment be manipulated to suppress
  • large patch?
  • 11. Name a contact, systemic and penetrant fungicide that will
  • control large patch.
  • 12. During what season(s) are preventive applications of large patch
  • fungicides applied in GA?
slide3

What was once consider one disease (Brown Patch) in now considered as three.

In this section we will review Large Patch.

BROWN PATCH

Yellow Patch

Cool Season Grasses

Rhizoctonia cerealis

Rhizoctonia Large Patch

Warm Season Grasses

Rhizoctonia solani

(strain AG 2-2 LP)

Brown Patch

Cool Season Grasses

Rhizoctonia solani

(strains AG 1 and

AG 2-2IIIB)

slide4

RHIZOCTONIA LARGE PATCH

caused by

Rhizoctonia solani

(strain AG 2-2 LP)

slide5

Rhizoctonia solani

(strain AG 2-2 LP)

  • Nonspore-forming fungus.
  • Survives as sclerotia or dormant mycelium
  • in thatch, soil or dead tissue.
  • Initial infection occurs on leaf sheaths when
  • night temps at 40-60°F and crowns of
  • plants have been wet for more than 10 hrs.

Note how Large Patch occurs at a lower temp. than Brown Patch

slide6

RHIZOCTONIA LARGE PATCH

Susceptible Grasses

All warm season grasses.

Note that large patch occurs only on warm season grasses while brown patch

occurs on cool season grasses.

slide7

RHIZOCTONIA LARGE PATCH

Favorable Environment

  • Night temps <60°F.
  • High soil moisture.
  • More than 10 hr. of crown and stolon
  • wetness per day for several days.

Lower temp. than

brown patch

slide8

About 8 ft. in diameter

Large patch on St.Augustinegrass – Patches can be

15 or more ft. in diameter.

slide9

Large patch on hybrid bermudagrass.

Symptoms occur in the spring and fall

when the turf is either coming out of

dormancy or going into dormancy.

slide10

perennial rye

Large patch on zoysiagrass.

Note how disease does not

spread to perennial ryegrass

at top of photo. Perennial rye,

a cool-season grass, is not

susceptible to the strain of

of R. solani that causes Large

Patch.

Large patch on zoysia

slide11

Large patch on hybrid bermudagrass

Outer margins of patches are

yellow to orange in color when

the large patch fungus is actively

growing and infecting turf.

Large patch on a zoysiagrass fairway

slide13

Large Patch on zoysia. Note how

weeds develop in center of patch.

Note orange border indicating active

disease development.

Large Patch on St. Augustinegrass.

slide14

Large patch beginning to develop on zoysia in the fall.

Patches (<1 ft. in diam.) of yellow-orange leaves are

an indication of early infection. As patches increase in

size, leaves in the center of the patch turn gray.

Look at leaf sheaths to make diagnosis

slide15

No lesions on

leaves.

Note lesions on

this leaf sheath

of St. Augustine.

This is where

the fungus is

infecting.

Development of

brown lesions on

leaf sheaths is the

best diagnostic

symptom of large

patch

slide16

Leaf turns yellow due to poor

translocation of nutrients and water

up through leaf sheath.

Lesion forms on leaf

sheath, not on leaf.

slide17

Note how lesions

do not form on

leaves, just on leaf

sheaths.

This is a difference

between large patch

and brown patch.

Lesions often

coalesce to

consume whole

leaf sheaths

slide18

ligule

Fungus rots leaf sheaths and leaves shrivel and die do to poor translocation of

water and nutrients. Fungus seldom grows past ligule and into the leaf.

slide19

Lesion on leaf sheath

of centipedegrass

slide20

Dark lesion on outer leaf

sheath of zoysiagrass

When outer leaf

sheath is stripped

away, inner lesion

may appear bleached.

slide21

MANAGEMENT OF

RHIZOCTONIA LARGE PATCH

slide22

MANAGEMENT OF

RHIZOCTONIA LARGE PATCH

Cultural Management

  • Avoid N fertility in spring prior to mid-May and in fall
  • after Sept. 1st.
  • - Maintain moderate to high P & K according
  • to soil test.
  • Decrease shade and increase air circulation.
  • - Improve soil drainage.
  • Avoid irrigation in late afternoon and in
  • evening prior to midnight.
  • - Maintain thatch at ½ inch or less.
slide23

MANAGEMENT OF

RHIZOCTONIA LARGE PATCH

Resistant Species and Cultivars

  • All warm season species are susceptible, but in
  • in general, bermudagrass will recover
  • faster than either zoysia, St. Augustine, pasalum
  • or centipede.
  • - No cultivars are known to be resistant.
slide24

Management of Large Patch

Chemical Control

Contact fungicides – chlorothalonil, mancozeb,

thiram, polyoxin. 14 days control

Localized penetrants – iprodione, vinclozolin,

trifloxystrobin, pyraclostrobin. 21 days control

Acropetal penetrants – azoxystrobin, flutolanil,

thiophanate-methyl, propiconazole, triadimefon,

fenarimol. 21-28 days control

slide25

Management of Large Patch

Chemical Control

Preventive or early curative* fungicide applications are recommended in

spring and fall when night temperatures are between 35 and 60°F.

*when patches are less than softball size.