Horne, C. Wendell

Walla, Walter J.

English

Texas A&amp;M Repository

/ 000)L-732CONTROL DISEASES IN THE HOME LAWNC. Wendell Horne and Walter J. WallaExtension Plant Pathologists • Texas A&M UniversityDisea e prevention is an important key to suc-cessful maintenance of a uniform, green livingcarpet around the home. The "green thumbgardener," who understands plant language andrespond' to symptoms before a problem develops,holds a prerequisite to efficient disease control.lVlo,t disease control chemicals act as protectantsand prevent infection from microorganisms thatenter plant tis ue 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 i characterized by circular pat-terns of dead gra s blades in the turf. These rangefrom 1 to 50 feet in diameter. Blades and sheathsare pulled easily from the stolons because of de-terioration in the attachment area. Stolons oftenremain green. ew 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. Diseasedevelopment occurs most rapidly in temperaturesbetween 75 and 85 degrees F. when free moistureis present. Fungus activity stops when the airtemperature reaches 90 degrees. This explainsea ona I developmen t.Some lawns are affected almost every year,while others are damaged only occasionally. Fungi-cide application, which effectively prevents brownpatch development, should be made when brownpatch is expected. On lawns where brown patchoccurs occasionally, apply fungicide when the dis-ease first appears. See fungicide chart for specificrecommenda tions.Gray Leaf SpotGray leaf spot causes irregular brown to grayspots on leaf blades of St. Augustine grass. This7.2disease, caused by a fungus, develop' rapidly withabundant moisture and wartn temperature. Itis usually noticed first in shaded areas that remaindamp for some time. In areas of heavy di easedevelopment, the grass may have a burned orscorched appearance resulting from death or spot-ting of the leaf blades. Lesions al'o occur on stemsand spikes of affected plants.Disease severity is enhanced by exee 'ive nitro-gen 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 exce -sive nitrogen fertilization. Water during the day,so that foliage will not remain wet overnight.Most turf fungicides control this di ease effectivelywhen used at 10-day intervals during periods favor-able for infection. (See fungicide chart.)Helminthosporium Leaf Spot;Root Rot of BermudagrassSymptoms of this fungal disease appear as irreg-ular 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 act as a pathogenwhen weather conditions favor its developmentduring the growing season. Chemical fungicide 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 lawnswhere the grass thins and becomes unsightly. Thiscondition develops more rapidlY during the sum-mer when large dead areas appear in the turf. Afungus (Curvularia spp.) can be cultured fromstolons of diseased grass, but reproducing infec-tions on healthy grass is difficult. For this reason,T xas M Univ rsity • Agricultural Ext nSt. AugustinegrassThatch} resulting from leaf clippings and deadstolons} may accumulate in thick layers resultingin poor root development and inefficient waterpenetration. Leaves and roots are produced atnodes on surface of stolons} and these roots mustpenetrate thatch before reaching soil} making themhighly susceptible to drouth.it i believed thi fungus causes fading-out on grassweakened by other disease-causing organisms, insectpe ts or nematodes.Effecti e control of fading-out requires severaldifferent approaches. First, correct cultural condi-tions that limit plant growth. Mowing at theproper height, fertilizing according to soil test,watering properly and avoiding thatch build-up allcontribute to healthy grass that resists develop-ment of weak pathogens.Accumulations of fallen clippings and deadleaves, commonly referred to as "thatch," providean environment favorable for microorganism build-up (see drawing). In fact, activity of these organ-i ms is necessary for converting this material intohumus. Some types become overambitious, how-ever, and begin deriving nourishment from livinggra s plant, resulting in the fading-out condition.These areas sometimes are difficult to resod wheregra s has died.l.~hatch build-up can be prevented by catchinggra s clippings or by removing leaf accumulationsby close mowing and raking just before springgrowth begins. Follow with regular mowings whichremove only short clippings that dehydrate rapidlyand do not contribute to thatch build-up.Fungicide applications hasten recovery of af-fected 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 nutri-ents 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, how-ever, the affected grass may decline rapidly if cor-rective 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 fungusSclerotinia horneocarpa. The disease appears 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, ap-pearing like fine cobweb growth, may be pre enton leaf blades in early morning dew. Thi di easecan occur any time during the year but it is mostprevalent in late spring or early fall along withhot humid days and cool nights. Improved ber-mudagrass, zoysia and bahiagrass are the mostseverely affected grasses grown in Texas.Control is accomplished by applying adequatenitrogen and spraying with a turf fungicide if thedisease occurs (see fungicide chart).Pythium BlightPythium blight (cottony blight) is caused bythe fungus Pythium aphanidermatum and affectimproved bermuda grasses. Infected grass rapidlydies in spots or streaks. In early stages of infection,the affected grass appears water-soaked, soft andslimy and exhibits a greasy appearance. At timesthe affected spots may have a "cottony" appear-ance 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 develop-ment.Slime MoldsSlime molds are fungi which develop mostlyduring warm, moist weather. The most commonslime mold (Physarum cinereum) found on turf-grass 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,grass blades, etc., to produce spores. They do notfeed on green plants and cause no damage otherthan shading. Remove from lawn grass by apply-ing water under pressure with a water hose or bybrushing 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 sys-temically 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 anuisance than a threat to turf health, controlusually is directed toward preventing seed headdeveiopment. Adequate watering and fertilizationhelps prevent seed head development which occursunder stress conditions. Close mowing may removeseed heads when produced.RustRust, a fungal disease (Puccinia spp.), is mostdamaging during mild, warm weather. Plants af-fected with rust have a cholorotic appearance, andstands may begin to thin. Orange colored linearpu tules or raised bumps are evident on leaf blades.These vary in appearance, depending on the speciesinvolved. Pustules are difficult to see on affectedSt. ...c\.ugustine 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 symptoms often appear asareas of low fertility, even where fertilizers havebeen applied. This occurs when nematodes feed-ing 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 that infect injured or devitalized roots.Identify nematode problems positively beforetaking corrective action with chemicals. The PlantNematode Detection Laboratory located at CollegeStation analyzes soil samples for the presence ofnematodes. Growers can obtain information sheet,bags and mailing carton from the county Exten ionagent's office.Materials suggested for chemical control ofnematodes are Nemagon, Fumazone and VC-13.The first two materials mentioned often orne inlarge containers, thus it may be de irable to obtainthe services of a commercial applicator. The thirdmaterial, a phosphate insecticide, must be workedinto the soil well since diffusion is slow. Granular-type nematocides, such as ematode-Killer andNema-X, are available. These are effective if ameans of working them into the soil is devi ed.Where nematodes constitute the limiting growthfactor, a nematocide application usually is neededyearly. Nematodes are seldom completely elimi-nated from the soil, but their population can bereduced to allow normal plant growth. Goodcultural and fertilization practi es al 0 help over-come nematode injury.Iron ChlorosisIron chlorosis results from iron deficiency inthe soil. Iron may not be available becau e of analkaline soil reaction, changing the element to aform unsuitable for the plant. This condition iscorrected by applying iron sulfate ( opperous) oriron chelates (see chart).This condition is typified by yellowing of thefoliage. Often green and yellow streak inter-mingle. In extreme conditions, the leave are solidyellow.VirusA virus condition of St. Augustine grass hasbeen identified which causes a chlorotic mottle ofthe leaf blades. Affected grass is un thrifty and thinsFairy ringsbadly. Spread and control of this condition is cur-rently under investigation.Other Problem CausesSoil compaction-Certain soils are compactedeasily, 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 inchesin diameter may appear in areas frequented byfemale dogs. Heavy watering helps correct thiscondition.Fertilizer burn-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 ex-poses 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 recom-mendations.Shock-Allowing grass to become too tall beforemowing causes grass to experience shock and losevigor. Mow frequently to prevent this condition.Permanent wilt-Grass allowed to become toodry may pass the permanent wilt stage where recov-ery is not possible. This may occur where waterdoes not penetrate because of compaction.Fungicide, Nematocide RecommendationsUse fungicides and nematocides to protect turfduring periods favoring disease development. Theiruse should supplement good cultural practices.Fungicides and nematocides are capable of inhib-iting 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 organi ms.Selected ReferencesI. Cole, Herbert and Houston Couch, 1963, Con-trol Turfgrass Diseases - Circular 510, ThePennsylvania State Univer ity, University ParkPennsylvania.2. Freeman, T. E., 1967, Diseases of SouthernTurfgrasses - 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. 1966-January 1967).ChemicalBenomylChloronebPCNBManeb andcoordinated zinc ionThlramCaptanCyc1ohexmi de + PCNBDaconi 1DexonDyreneKobanOBCPYC-13Iron SulfateIron ChelatesMATERIALS FOR OISEASE CONTROLTrade name Brown Helmi ntho- Grey Leaf 0011 ar Pythium Fadi ng- Nema- Ironand formulations Patch sporium Spot Spot Blight Rust Out todes ChlorosisTersan 1991 (WP)Tersan SP (WP)Terraclor (L.G.WP)Fore (WP)Thylate (WP)Acti-dione (WP)RZDaconil 2787(WP)Dexon (WP)Dyrene (WP)Koban (WP)Nemagon (L )Fumazone (L)Oxy-B8C-12 (I.)Nema-X (G )Nema-Kill (G)YC-13 (L )Copperas (WP)(Several )(L or WP)The product (s) mentioned herein does not guarantee nor warrant the standard of the product. nor does it implyapproval of the product to the exclusion of others which may be equally suitable.USE ALL PESTICIDES ACCORDING IQ. LABEL DIRECTIONSNote:L--L iquidG--GranuleWP--Wettable powderCooperative Extension Work in Agriculture and Home Economics, Texas A&M University and the United States Department ofAgriculture cooperating. Distributed in furtherance of the Acts of Congress of May 8, 1914, as amended, and June 30, 1914.15M-6-72, Revised PP

Control Diseases in the Home Lawn.

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Control Diseases in the Home Lawn.

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Control Diseases in the Home Lawn.

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