JUN Z '1 I ILA.)

s-

L-732

CONTROL OF DISEASES IN THE HOME LAWNC. Wendell Horne and Walter J. Walla

Extension Plant Pathologists • The Texas A&M University System

Disease prevention is an important key to suc­cessful maintenance of a uniform, green livingcarpet around the home. The "green thumbgardener," who understands plant language andresponds to symptoms before a problem develops,holds a prerequisite to efficient disease control.:Most disea 'e control chemicals act as protectantsand prevent infection from microorganisms thatenter plant tissue causing disease. The followingdescription helps early recognition and treatmentof potential problems.

Brown PatchBrown patch disease, caused by a fungus (Rhi­

zoctonia solani), occurs in the late spring or earlyfall. The disease is characterized by circular pat­terns of dead grass blades in the turf. These rangefrom I to 50 feet in diameter. Blades and sheathsare pulled easily from the stolons because of de­terioration in the attachment area. Stolons oftenremain green. New leaves may emerge in thecenter of the circular patch in 2 or 3 weeks, givingthe diseased area a doughnut shaped appearance.The entire spot eventually may become greenduring a long growing season.

St. Augustine grass is damaged more by brownpatch than bermudagrass or zoysiagrass. Diseasedevelopmcnt occurs most rapidly in temperaturesbetween 75 and 85 degrees F. when free moistureis present. Fungus activity stops when the airtemperature reaches 90 degrees. This explainsseasonal development.

Some lawns are affected almost every year,while others are damaged only occasionally. Fungi­cide application, which effectively prevents brownpatch development, should be made when brownpatch is expected. On lawns where brown patchoccurs occasionally, apply fungicide when the dis­ease first appears. See fungicide chart for specificrecommendations.

Gray Leaf SpotGray leaf spot causes irregular brown to gray

spots on leaf blades of St. Augustine grass. This

7.2

disease, caused by a fungus, devclops rapidly withabundant moisture and warm tempcrature. Itis usually noticed first in shaded areas that remaindamp for some time. In areas of heavy diseasedevelopment, the grass may have a burned orscorched appearance resulting from death or spot­ting of the leaf blades. Lesions also occur on stemsand spikes of affected plants.

Disease severity is enhanced by excessive nitro­gen fertilizer on certain types of St. Augustine grass.Newly-sprigged or rapidly-growing grass is moresusceptible than well established grass.

Control is best accomplished by avoiding exces­sive nitrogen fertilization. V\Tater during the day,so that foliage will not remain wet overnight.Most turf fungicides control this disease effectivelywhen used at 10-day intervals during periods favor­able for infection. (See fungicide chart.)

Helminthosporium Leaf Spot;Root Rot of Bermudagrass

Symptoms of this fungal disease appear as irreg­ular patches, ranging in size from 2 to several feetin diameter. Infections on leaves appear as small,olive green spots which enlarge to form darkblotches. Infected leaves die and fade to a lighttan color. The entire plant is killed when theroot rot phase of this disease develops.

The disease-causing fungus overwinters in thatchat the base of the plant and acts as a pathogenwhen weather conditions favor its developmentduring the growing season. Chemical fungicides areeffective in control. Apply at 7 to 14-day intervalsduring periods that favor disease development. Seethe fungicide chart for specific recommendations.

Fading-outFading-out is a serious problem in many lawns

where, the grass thins and becomes unsightly. Thiscondition develops more rapidlY during the sum­mer when large dead areas appear in the turf. Afungus (Curuularia spp.) can be cultured fromstolons of diseased grass, but reproducing infec­tions on healthy grass is difficult. For this reason,

Texas Agricultural Extension Service. The Texas A&M University System. John E. Hutchison, Director. College Station

St. Augustinegrass

Thatch, 1·es1llting frorn leaf clippings and deadstolons, rnay arcurnlllate in thick layers resultingin poor root developrnent and inefficient waterpenetrat ion. Leaves and roots are produced atnodes on sur/are of stolons, and these roots rnuslpenetrate thatch before reaching soil, rnaking lhernhighly ,\:llsceptible to drollth.

it is believed this fungus causes fading-out on grassweakened by other disease-causing organisms, insectpests or neina todes.

Effective control of fading-out requires severaldifferent approaches. First, correct cultural con(li­tions that li111it plant growth. lowing at theproper height, fertilizing according to soil test,watering properly and el\ oiding thatch build-up allcontribute to healthy grass that resists develop­ment of weak pathogens.

Acclunulations of fallen clippings and deadleaves, comlnonly referred to as "thatch," providean environlnent favorable for 111icroorganisln build­up (see drawing). In fact, activity of these organ­iSIns is necessary for converting this material intohumus. Some types becoine overalnbitious, how­ever, and begin deriving nourisillnent froll1 livinggrass plants, resulting in the fading-out condition.These areas sOluetimes are difficult to resod wheregrass has died.

l~hatch build-up can be prevented by catchinggrass clippings or by renl0ving leaf accumulationsby close mowing and raking just before springgrowth begins. Follow with regular Inowings whichremove only short clippings that dehydrate rapidlyand do not contribute to thatch build-up.

Fungicide applica tions hasten recovery of af­fected turf. However, use in combination withgood cuI tural practices.

Fairy RingsMushrooms in a circle or semi-circle are called

"fairy rings." According to ancient mythology,these result from fairies sowing seed as they dancein circles. In truth, however, these mushrooms arefruiting structures of fungi, produced when weatherconditions are favorable. Mushroom-producingfungi develop an organic matter in the soil andproduce fruiting structures on the outer limits ofthe colony, causing a circular effect. Grass is oftengreener in the ring area because of available nutri­ents liberated by decomposition of the fungus.Grass in the center of the ring may be decliningbecause of fungus activity.

Control often is not necessary because of thecondition's temporary nature. In other cases, how­ever, the affected grass may decline rapidly if cor­rective steps are not taken. In such cases, aeratethe soil by punching holes 6 to 8 inches deep atregular intervals. Apply a fungicide drench at astrength 2 or 3 times stronger than the normalrecommendation.

Dollar Spot - Small Brown PatchDollar spot of turfgrass is caused by the fungu

Srlcrotinia hOlneocarpa. The disea e appear asround, brown or bleached spots the size of a silverdollar or slightly larger. Lesions may be seen onthe edges of leaf blades. These cau e death of leaftips. During disease activity, fungal growth, ap­pearing like fine cobweb growth, may be pre enton leaf blades in early luorning dew. This diseasecan occur any time during the year but it is mostprevalent in late spring or early fall along withhot humid days and cool nights. Improved ber­111udagrass, zoysia and bahiagrass are the mostseverely affected grasses grown in Texas.

Control is accoll1plished by applying adequatenitrogen and spraying with a turf fungicide if thedisease occurs (see fungicide chart).

Pythium BlightPythium blight (cottony blight) is caused by

the fungus Pythillrn aphaniderrnaturn and affectsinlproved beriTIuda grasses. Infected grass rapidlydies in spots or streaks. In early stages of infection,the affected grass appears wa ter-soaked, soft andsliiny and exhibits a greasy appearance. At timesthe affected spots may have a "cottony" appear­ance due to the abundant fungal growth. Thedisease occurs during warm, humid weather inpoorly drained areas. Fungicides are effective incontrol. A 7 to 14 day spray schedule should befollowed during periods favoring disease develop­ment.

Slime MoldsSlime molds are fungi which develop mostly

during warm, moist weather. The most COlllmon

slime Inold (Physa'fum cinercum) found on turf­grass occurs as a dark gray to black crust-likematerial. The soot-type material rubs off easilyon shoes or clothing.

Slime molds derive nourishment from decayingorganic matter in or on the soil. Under certainconditions, they move upward on sticks, stones,gra s blades, etc., to produce spores. They do notfeed on green plants and cause no damage otherthan shading. Remove from lawn grass by apply­ing water under pressure with a water hose or bybru hing with a broom.

SmutSmutted bermudagrass seed heads are a nuis­

ance when the black spores rub off on shoes andclothing. These occur when the plants are sys­temically infected with smut fungus (Ustilagocynodontis).

Conventional fungicides do not prevent thiscondition, because they are protective and do notenter plant parts. Since this disease is more of anui ance than a threat to turf health, controlusually is directed toward preventing seed headdevelopment. Adequate watering and fertilizationhelp prevent seed head development which occursunder tress conditions. Close mowing may removeseed heads when produced.

RustRust, a fungal disease (Puccinia spp.), is Inost

damaging during Inild, warm weather. Plants af­fected with rust have a cholorotic appearance, andstands Inay begin to thin. Orange colored linearpu ,tules or raised bunlps are evident on leaf blades.These vary in appearance, depending on the speciesinvolved. Pustules are difficult to see on affectedSt. Augu tine grass unless the blades are examinedwith a hand lens. Zoysiagrass is affected morethan either St. .Augustine or bermudagrass. Rustdiseases can be controlled by using fungicides. (Seefungicide chart.)

NematodesNematode injury sYlnptolns often appear as

areas of low fertility, even where fertilizers havebeen applied. This occurs when nematodes feed­ing on roots reduce their ability to absorb waterand nutrients. These tiny roundworms whichmeasure about 1/50 of an inch long have a spearin their mouth part that punctures plant cells andwthdraws cell sap. This activity not only removescell contents but opens points of entry for otherorganisms tha t infect injured or devi talized roots.

Identify nematode problems positively beforetaking corrective action with chemicals. The PlantNematode Detection Laboratory located at CollegeStation analyzes soil samples for the presence of

nematodes. Growers can obtain information sheets,bags and mailing cartons from the county Extensionagen t's office.

Materials suggested for chemical control ofnematodes are Nelnagon, Fumazone and VC-13.The first two materials mentioned often come inlarge containers, thus it I1lay be desirable to obtainthe services of a commercial applicator. The thirdInaterial, a phosphate insecticide, must be workedinto the soil well since diffusion is slow. Granular­type nematocides, such as ematode-Killer andNema-X, are available. These are effective if ameans of working them into the soil is devised.

Where nematodes constitute the limiting growthfactor, a nelnatocide application usually is neededyearly. Nematodes are seldoln cOlnpletely elimi­nated from the soil, but their populations can bereduced to allow normal plant growth. Goodcultural and fertilization practices also help over­COl1le nematode injury.

Iron ChlorosisIron chlorosis results froln iron deficiency in

the soil. Iron may not be available because of analkaline soil reaction, changing the elelnent to aform unsuitable for the plant. This condition iscorrected by applying iron sulfate (copperous) oriron chelates (see chart).

This condition is typified by yellowing of thefoliage. Often green and yellow streaks inter­Iningle. In extreme conditions, the leaves are solidyellow.

VirusA virus condition of St. Augustine grass has

been identified which causes a chlorotic mottle ofthe leaf blades. Affected grass is unthrifty and thins

Fairy rings

badly. Spread and control of this condition is cur­rently under investigation.

Other Problem CausesSoil c01l1.paction-Certain soils are compacted

easily, especially in areas of heavy foot traffic.This condition prevents adequate penetration ofmoisture and nutrients and restricts root systemgrowth.

Several types of aerafiers correct his condition.Dog urine injury-Circular sports 8 to 10 inches

in diameter may appear in areas frequented byfemale dogs. Heavy watering helps correct thiscondition.

Fertilizer bllrn-Commercial fertilizers are saltsand can burn grass when applied excessively. Thiscondition is most often seen where fertilizers werespilled.

Excessive shading-Most lawn grasses requirerather high light intensities. When a lawn isfertilized, this in turn stimulates growth of shrubsand trees that shade the grass. Selective pruningof trees and shrubs helps correct this condition.

Sun scald-Clipping grass too closely removesfoliage necessary for food manufacturing and ex­poses stolons to direct sun rays. When this occurs,a brown lesion or burned area is found on theupper surface of the stolon. Avoid mowing tooclosely.

Improper fertilization-Excessive use of anindividual element, such as nitrogen, makes plantsmore susceptible to disease attack. Avoid thisproblem by fertilizing according to soil test recom­mendations.

Shock-Allowing grass to become too tall beforemowing causes grass to experience shock and losevigor. Mow frequently to prevent this condition.

Pennanent wilt-Grass allowed to become toodry may pass the permanent wilt stage where recov­ery is not possible. This may occur where waterdoes not penetrate because of compaction.

Fungicide, Nematocide Recommendations

Use fungicides and nematocides to protect turfduring periods favoring disease development. Theiruse should supplement good cultural practices.Fungicides and nematocides are capable of inhib­iting or killing certain types of microorganisms onplants or in the soil.

No chemical kills all undesirable organisms andspares all desirables. Disease control chemicalsshould be used only when needed. The followingchart suggests materials found most effective againstspecific disease causing organisms.

Selected References

1. Cole, Herbert and Houston Couch, 1963, Con­trol Turfgrass Diseases - Circular 510, ThePennsylvania State University, University ParkPennsylvania.

2. Freeman, T. E., 1967, Diseases of SOllthernTurfgTasses - Tech. Bulletin 713, University ofFlorida, Gainesville, Florida.

3. Gould, Charles .J., 1967, Use of Fungicides inControlling Turfgrass Diseases. Reprint of TheGolf Course Superintendent (Sept. jOct. 1966­January 1967).

Chemical

MATERIALS FOR DISEASE CONTROL

Trade name Brown Helmintho- Grey Leaf Dollar Pythium Fading- Nema- Ironand formulations Patch sporium Spot Spot Blight Rust Out todes Chlorosis

Benomyl Tersan 1991 (WP) X XChloroneb Tersan SP (WP) XPCNB Terraclor (L,G,WP) XManeb and Fore (WP) X X X Xcoordinated zinc ionCaptan XCyclohexmide + PCNB Acti-dione (WP) X

RZChlorothalonil Daconil 2787 (WP) X X X XDexon Dexon (WP) XDyrene Dyrene (WP) X XKoban Koban (WP) XDBCP Nemagon (L ) X

Fumazone (L ) XOxy-BBC-12 (L ) XNema-X (G ) XNema-Kill (G ) X

VC-13 VC-13 (L ) XIron Sulfate Copperas (WP) XIron Chelates (Severall (LorWP) X

The product (sJ mentioned herein does not guarantee nor warrant the standard of the product, nor does it imply approval of the productto the exclusion of others which may be equally suitable.

USE ALL PESTICIDES ACCORDING TO LABEL DIRECTIONS

Note:

L - Liquid

·G - GranuleWP - Wenable powder

Educational programs conducted by the Texas Agricultural Extension Service senJe people of all ages regardless of socia-economiclevels, race, color, sex, religion or national oTigin.

Cooperative Extension Work in Agriculture and Home Economics, The Texas A&M University System and the United StatesDepartment of Agriculture cooperating, Distributed in furtherance of the Acts of Congress of May 8, ]914, as amended, andJune 30, 1914.15 1-6-75, Reprint PP