Warm-Season Turfgrass Disease Management In Urban

E-3065/11Warm-Season Turfgrass DiseaseManagement in Urban LandscapesYoung-Ki Jo and Anthony Camerino*To prevent or minimize turfgrass diseasesin urban areas, a homeowner or landscapemanager needs to know the causes of turfgrassdiseases, identify and treat the disease as early aspossible in its infection cycle, and follow best management practices to keep the grass healthy.Host: The most effective management strategyfor turfgrass disease is to plant a disease-resistantturfgrass cultivar. However, few cultivars resist alldiseases. Also, a landscape typically already hasan established turfgrass, and replacing it with adisease-resistant cultivar is expensive.For existing turfgrass, the most practical waysto promote lawn health are to use good management practices, such as mowing, irrigating, andfertilizing properly, and applying fungicides onlywhen needed.Pathogen: There is no practical method toeradicate plant pathogens from a given landscape.Because most turfgrass pathogens occur everywhere in the environment, all turfgrass areascontain some level of disease. Often the diseaseoutbreak is so limited that it cannot be detectedeasily.However, fungicides can be used to reducediseases enough to minimize costs and keep theturfgrass quality at an acceptable level.Environment: Although we cannot alterenvironmental conditions on a large scale, we caninfluence the microenvironment of the turfgrassarea by implementing sound management practices. These practices include scheduling irrigationproperly, removing thatch, aerating the soil, andremoving or pruning trees to reduce shade andimprove airflow.Causes of turfgrass diseasegenPathostHoA plant disease occurs when a disease-causingmicroorganism (pathogen) infects a plant, givingall or part of the plant an abnormal appearance.Three componentsmust be present for aturfgrass disease tooccur: a susceptiblehost plant, a pathogen,Diseaseand the environmental conditions thatEnvironmentfavor the disease. IfFigure 1. Disease triangle.any component of thedisease triangle (Fig. 1) is absent, the disease willnot occur.To reduce the potential for disease pressure onturfgrass, implement management strategies foreach component of the disease triangle.*Assistant Professor and Extension Turfgrass PathologySpecialist, and Commercial Horticulture Extension Agent–Harris County; The Texas A&M University System1

Diagnosing turfgrass diseasesPreventing future disease outbreaksEvery lawn maintenance practice can eitherhelp or hurt a lawn. In some situations, the bestmanagement option may be to replace problemturfgrass with other non-turfgrass plants that aremore suitable for the environmental conditionsand the level of expected maintenance.If replacing the lawn is not an option, you willneed to adopt management practices that deterdiseases. These practices can be divided into fourmajor categories: cultural practices, chemicalapplications, use of disease-resistant turfgrass, andbiological control.Cultural practices: To promote healthy turfgrass and create the microenvironmental conditions that discourage disease development, adoptbest management practices for mowing, watering,and fertilizing the lawn: Mow often enough to avoid removing morethan one-third of the leaf blade during amowing. In the summer, with adequate rainfall and consistent fertilizer applications, youlikely need to mow every 5 days or possiblymore often to keep your lawn healthy. Irrigate infrequently and with enough waterto reach deep into the soil profile. The besttime to irrigate is the early morning. Waterthe area uniformly to prevent excessively wetor dry spots. An irrigation system checkupmay be needed to determine if your systemirrigates uniformly. Ideally, you should wateronly when a large area of the lawn showsearly symptoms of drought stress, such asfolding of grass blades. Choose and apply fertilizers accordingto need as determined by a soil analysis.For home lawns, do not apply more than1 pound of soluble nitrogen applicationper 1,000 square feet of lawn. Too muchnitrogen produces excessive lush growth,which is more susceptible to insect pests anddiseases. Using slow-release nitrogen sourcemay help reduce incidence of some diseases.Chemical applications: Fungicides can slowthe development of a disease and prevent its spreadto unaffected plants. Follow these guidelines toincrease the chances of success:If the quality of your turfgrass is poor, the causecould be pest insects or plant diseases. But moreoften it is caused by poor environmental conditions such as heavy shade, soil compaction, buriedconstruction debris, inappropriate soil fertility,and chemical damage. Poor mowing and irrigationpractices also can harm the microenvironment ofthe lawn.The information in Figure 2 can help you diagnose diseases and other common causes of poorturfgrass quality.Managing turfgrass diseasesOnce you have identified the primary cause ofa plant disease, determine your plan of action. Disease management requires a two-step approach:(1) promoting turfgrass recovery, and (2) preventing future disease occurrences.Promoting turfgrass recoveryTo help turfgrass recover from disease, irrigate properly, add fertilizer according to soil testresults, and apply herbicide to control weeds.However, remember that applying too much water,fertilizer, or herbicide can damage the grass.For example, large patch (often referred to asbrown patch), a disease caused by Rhizoctoniasolani, is more severe when turfgrass is stressed bythe presence of too much nitrogen and/or water inthe soil. Use water and fertilizer judiciously to helpthe grass recover and to avoid creating conditionsthat favor large patch.If fungal disease is severe, you may need toapply a fungicide to the turfgrass. Although it willnot cure turfgrass that is already dead or dying,the fungicide will stop the spread of the diseaseand protect unaffected areas.The timing of the application is critical: ifapplied too late, the fungicide may be ineffective due to the advanced stage of the infection. Inmany cases disease symptoms get worse immediately after a fungicide application because unseeninfections begin to develop. Remember: whenapplying a fungicide, your primary goal is to protect uninfected plant tissue.2

START: Distinctpatches of lush green,yellow to brown, ordead turfgrassDisease Identification KeyYESRing or arc of lush growth or deadgrass; mushrooms may be presentFairy ringYESNONOAffected areas are distinct circularpatches with red/brown edges; leafpulls out of leaf sheath very easily;most prevalent in the fall and springNo distinct patches;only leaf tissue affectedNOLarge patchYESNOAffected area has irregular patches ofyellow and dead grass; roots are shortand black; stolons may be rottedTake-all patchYESNOFrost injuryPatches appear quickly/overnight aftercold weather; patches are arranged ina camouflage-like patternYESNOIrregular patches appear quickly/a fewdays to weeks in drier areas duringhot weather; insects found in thethatch; roots presentChinch bugsYESNOOrange spots onleaves; spots rub offeasilyGrass gradually thins, yellows, anddies; irregular brown patches; grasspulls up easily; c-shaped larvae in soil;vertebrate animals may be attracted tothe affected areaGrubsYESRustYESNODistinct dead spots,often with yellowmargins and brown/gray interiorLeaf spotYESNONo leaf spots present;leaf blade covered witha dusty or slimy growththat rubs offSlime moldYESFigure 2. Dichotomous key of turfgrass diseases and disorders.3

Accurately identify the primary pathogen. Choose the correct fungicide for the patho-ucts), assume that the product will damageyour lawn unless applied accurately. If you areunsure of how to apply a product correctly, contactyour local county Extension agent.Host resistance: The easiest and most costeffective method to manage turfgrass diseases isto plant species and cultivars that are resistant todiseases. Unfortunately, in most situations it is notpractical or economical to replace a lawn with aresistant cultivar.Biological control: The use of living microorganisms to control pathogens is called biologicalcontrol. A few biological control products havebeen approved for turfgrass disease management.However, studies need to be conducted toprove that these products can consistently reducediseases in turfgrass across a range of environmental conditions. These products’ performanceis especially sensitive to environmental conditionsduring storage and application. Just as the pathogens infecting your lawn are influenced by environmental conditions, these products will likelybe effective only under specific environmentalconditions.gen. Apply the fungicide according to label usedirections. Make the application just before or veryearly in disease development. If an area hasa history of disease, note when the diseaseoccurs and under what environmentalconditions. Fungicides are most effective ifapplied just before infection is likely.Table 1 lists the fungicides approved forhome-owners to treat turfgrass disease. However,regulations change often, so read the label carefully before buying and using a fungicide. Tables2 and 3 list fungicides for professionals to use ongolf courses, for sod production, and for specificdiseases and conditions on turfgrass.Follow the directions exactly, especially thoselisting application rates and environmental conditions. Many fungicide labels specify the turfgrassspecies as well as environmental conditions thatmay cause chemical damage. When applying anymaterial (pesticide, fertilizer, or other prod-Table 1. Fungicides for homeowner use on turfgrass lawns.Common nameTrade names for homeowner usethiophanate-methylFungo 50, Fungo Flo, Scott’s Lawn Fungus Control, Southern Ag Thiomyl, Bonide Lawn andLandscape Granules Lawn and Landscape Systemic Disease Control; Bonide Infuse Lawn &Landscape GranulesmyclobutanilSpectracide Immunox Lawn Disease Control Concentrate, Spectracide Immunox LawnDisease Control Granules, Ferti-lome F-Stop, Green Light Fung-Away Systemic LawnFungicidepropiconazoleFert-lome Liquid Systemic Fungicide; Monterey Fungi-Fighter, Bonide Fung-onil Lawn andGarden Disease Control, Bonide Infuse Concentrate Systemic Disease Control, Ortho LawnDisease Control; Bonide Infuse concentrate; Bonide Infuse RTS; Bayer Fungus Control forLawns Ready to Spray; Bayer Fungus Control for Lawns Ready to Spread Granulesmono- and di-potassiumsalts of phosphorous acidMonterey Agri-Fos Systemic FungicideazoxystrobinMaxide Disease Killercopper octanoateBonide Liquid Copper Fungicide Concentratepotassium bicarbonateMonterey Bi-Carb Old Fashioned Fungicide4