6 pp., 4 photos, 1 illustration, 1 map, 1 illustrated decision guideWhite grubs are the larval stage of insects commonly known as May or June beetles. A few species commonly damage turfgrass and other cultivated plants. This publication includes biological and management information

Biles, Stephen

Merchant, Michael E.

Mott, Dale

Texas A&amp;M Repository

White grubs are the larval stage ofinsects commonly known as Mayor June beetles (or Junebugs). Texashas almost 100 species of these bee-tles, most of which do not causesignificant economic damage tocrops or horticultural plantings. Afew species, however, commonlydamage turfgrass and other culti-vated plants.  White grubs, sometimes referred toas grubworms, injure turf by feed-ing on roots and other under-ground plant parts. Damaged areaswithin lawns lose vigor and turnbrown (Figure 1). Severely dam-aged turf can be lifted by hand orrolled up from the ground like acarpet.  The most important turfgrass-infesting white grubs in Texas arethe June beetle, Phyllophaga crinita(Figure 2), and the southernmasked chafer, Cyclocephala lurida.Warm season grasses like bermuda-grass, zoysiagrass, St. Augustinegrassand buffalograssare attacked readilyby both types ofwhite grubs, withmost lawn damageoccurring during sum-mer and fall months.  Cool season grasses such as the fes-cues, bluegrass and ryegrass arealso susceptible to the June beetleand southern masked chafer,though such grasses tend to beattacked more frequently by aMay beetle, Phyllophaga congrua.Damage from May beetles oftenappears in the spring and earlysummer, before injury from otherwhite grubs becomes evident.Other white grub species occasion-ally recorded as pests in Texas turf-grass include Cyclocephala pasade-nae and Phyllophaga submucida.  Another interesting kind of whitegrub is the green June beetle,Cotinus nitida. These rather largegrubs feed primarily on decayingorganic matter and normally donot injure turf; however, turf canbe damaged by their burrowingactivity. Larvae are especially com-mon underneath fruit trees, incompost piles and in soils withhigh organic content, such as maybe found in heavily mulched gar-dens and flower beds. Daytimeresting places of green June beetlelarvae can often be found nearsuch sites and are marked by smallmounds of soil on the lawn sur-face. The larvae have a curioushabit of crawling on their backsacross the soil surface to movefrom one site to another. Adults ofthe green June beetle are velvet-green on the top, metallic greenbelow and approximately one inchlong. Adults fly during the day andfeed on over-ripe fruit.  E-2116/04White Grubs inTexas TurfgrassMichael Merchant, Stephen Biles and Dale Mott**Extension Urban Entomologist and ExtensionAgents-IPM, respectively, for Texas CooperativeExtension, The Texas A&M University System.Figure 1. Golf course fairway dam-aged by white grubs.Figure 2. Adult white grubs, oftencalled May or June beetles, are com-monly attracted to lights at night.Life CycleMost turfgrass-feeding white grubsin Texas, such as the June beetleand southern masked chafer,require 1 year to complete their lifecycle (a 2-year cycle is suspected ina portion of the grub populationsin north Texas). The May beetle,Phyllophaga congrua, requires 2years to develop. For simplicity, thefollowing discussion will be limitedto species with 1-year life cycles.Once a year, in late spring orsummer, adult beetles emerge fromthe soil to mate. Mated femalesthen return to the soil to lay eggs.Within about two weeks the eggshatch into small white grubs thatfeed on grass roots. The pupa, orintermediate stage between thelarva and the adult, occurs the fol-lowing spring and is the last imma-ture phase of the insect's develop-ment cycle. Adults subsequentlyemerge from the pupal stage whenenvironmental conditions arefavorable in early- to mid-summer.Most damage from white grubsoccurs during mid-summer toearly-fall when the larger larvae areactively feeding.Adult. The adult stage of thevarious white grub species areheavy-bodied beetles, 1⁄ 2 to 5⁄8 inchlong, brown, with long, spindlylegs (Figure 2). The June beetle andsouthern masked chafer emergefrom the soil and fly at night, usu-ally after a significant rainfall orirrigation. Flight periods may lastfor several weeks, during whichtime mating and egg-laying occur.During flights, large numbers ofadult beetles, primarily males, maybe attracted to lighted windows orother lights at night. Females,being less active fliers, usually areless common around lighted areasthan are males. For this reason,turning off outdoor lights duringadult flight periods may not sub-stantially reduce subsequent whitegrub damage. Heavy white grubinfestations often can be found inareas with little or no outdoorlighting.After mating, female beetles dig 2to 5 inches into the soil to lay eggs.Each female can lay up to 30 to 40eggs, which hatch in approximate-ly two weeks.Larva. White grub larvae arecreamy white and C-shaped, withthree pairs of legs (Figure 3). Afterhatching, the white grub passesthrough three larval life-stages, orinstars. These instars are similar inappearance, except for their size.First- and second-instars eachrequire about 3 weeks to develop tothe next life-stage. The third-instaractively feeds until cool weatherarrives. Third-instar larvae areresponsible for most turfgrass dam-age due to their large size (1⁄2 to 1inch-long) and voracious appetites.Feeding by large numbers of third-instar white grubs can quicklydestroy turfgrass root systems, pre-venting efficient uptake of foodand water. Damaged turf does notgrow vigorously and is extremelysusceptible to drying out, especial-ly in hot weather.When cool weather arrives, whitegrubs become dormant until thefollowing spring. During this dor-mant period white grubs do littleor no feeding and cause little dam-age. Occasionally white grubs willbe found in turfgrass areas that failto green up in the spring; however,the damage is primarily the resultof feeding that occurred the previ-ous fall. Spring and winter treat-ments for white grubs with 1-yearlife cycles generally are ineffectivein preventing turf damage. Pupa. The pupal stage follows thethird-instar and is the life stageduring which the white grub trans-forms, or metamorphoses, into anadult beetle. The pupal stage doesnot consume food and does notmove through the soil. This lifestage occurs during the spring andlasts approximately 3 weeks. Pupaecan be found in small earthen cellsthree to six inches below the soilsurface. White grub treatmentsapplied during the pupal life stageare both ineffective and unneces-sary.Managing White GrubsKnowing when you have a prob-lem. White grub damage can bedetected by the presence of irregu-lar-shaped areas of weakened ordying grass in the lawn. Less-severely damaged turf lacks vigorand is more vulnerable to invasionby weeds. Depending on locationwithin the state, damage mayappear any time between themonths of June and October.Turfgrass damaged by white grubshas a reduced root system and iseasily pulled from the soil. Grubsshould be readily found in the topfew inches of soil, in the turfgrassroot zone. Turfgrass usually recov-ers from white grub damage by fallor the following spring.  Figure 3. Turfgrass-infesting whitegrub larvae feeding on grass roots.Grubs are most damaging when theyreach a length of 1⁄2- to 1-inch.At least one turfgrass disease,Take-all Patch, can sometimes bemistaken for white grub damage.Take-all Patch occurs most fre-quently in spring and early sum-mer and can be distinguished bythe rotted appearance of the roots.In contrast with white grub dam-age, dead spots caused by Take-allPatch may persist into the summermonths.Some Texas lawns never sufferwhite grub damage, while othersare damaged year after year. If yourlawn consistently dies out inpatches during late summer and ifyou can verify that white grubs arethe culprits, you may benefit froma preventative treatment.  On theother hand, if you want to mini-mize your use of insecticides anddon’t mind sampling for whitegrubs, follow the quick decisionguide on page 6. By confirmingthat you have white grubs beforetreating your yard, you can avoidspending money on grub controland reduce pesticide use.  To confirm whether you need totreat for grubs, examine several soilsections at least 3 to 4 inches acrossand 4 inches deep (sample sandysoils to greater depths). A good ruleof thumb is to examine several soilplugs (up to one square foot per1000 square feet of turf) from wide-ly scattered parts of the lawn. Takecare to include areas at the edges ofsuspected grub damage. Findingmore than five white grubs persquare foot justifies treatment,although some lawns with evenhigher numbers of grubs may showno damage.Non-chemical controls. Severalnon-chemical treatments are avail-able for controlling white grubs.Beneficial nematodes within thegenera Steinernema and Heterorhab-ditis are tiny worms that attackwhite grubs and other soil inhabit-ing insects. These microscopicworms can be purchased in storesor through garden supply catalogs.Commercial nematode productsare usually designed to be mixedwith water and applied to lawnsusing a hose-end or hand-heldsprayer. Recent research shows thatunder good conditions commer-cially-available nematodes canreduce white grub populations by50% or more.Nematodes must be supplied withadequate moisture to help themmove down into the soil wheregrubs are feeding.  At least 1⁄ 4 inchof water should be applied before,and another 1⁄ 4 inch of waterapplied just after, nematodes aresprayed on the lawn. These wormspose no threat to humans or land-scape plants and are an environ-mentally sound alternative forthose who prefer not to use pesti-cides on their lawn.One microbial pesticide, Bacilluspopilliae, or milky spore disease,often is recommended for whitegrub (Japanese beetle) control inother regions of the U.S.; however,it has not been shown to be effec-tive against Texas turf-infestingwhite grubs.Spiked sandals sold for aeratingturf have been tried with some suc-cess for controlling damaging grubpopulations. According to onestudy, repeatedly walking overheavily infested turf with thespiked sandals may reduce grubpopulations up to 50%. These san-dals are available through severalgarden supply catalogs.Chemical control. Proper timingand chemical application are criti-cal to suppressing white grubs.New white grub insecticides aremore persistent and less toxic tobeneficial arthropods and earth-worms. However, these treatmentsmust be applied early enough tokill the smaller (less than 1⁄2-inch-long) larvae. Once white grubsreach the third-instar life stage,they are more difficult to controlwith the new products.The insecticides imidacloprid andhalofenozide are used most todayfor white grub control. Imidaclo-prid is most effective against small-and medium-sized grubs but maykill some grubs larger than 1⁄2 inchlong. Imidacloprid trade namesinclude Merit®, Bayer AdvancedLawn™ Season Long Grub Controland Scott's® Grub-Ex®. The lethaleffects of the insect growth regula-tor halofenozide are limited toearly white grub life stages.Halofenozide is ineffective ifapplied too late, after grubs havereached the third-instar life stage.Halofenozide trade names includeMach 2, Spectracide® Grub Stop™and Hi-Yield® Kill-a-Grub™.Fortunately, both halofenozide andimidacloprid can be applied earlyand persist in the soil. Ideally, bothproducts should be applied withinsix weeks of egg-laying. In southTexas, apply insecticides for whitegrubs in early- to mid-June. In cen-tral and north Texas, the optimaltreatment time is early- to mid-July. Where grub damage is already evi-dent in lawns and larger grubs arepresent, use products containingtrichlorfon or carbaryl. Becausethey bind to soil particles andremain close to the surface evenafter irrigation, pyrethroid insecti-cides (such as permethrin, esfen-valerate, cyfluthrin and bifenthrin)are less effective against whitegrubs, especially in clay soils.  Post-treatment irrigation is essen-tial for all grub-control products.To ensure that insecticides reachthe root zone, water-in liquid for-mulations with 1⁄2 to one inch ofwater immediately after applica-tion. Irrigate granular formulationswithin 24 hours to wash theinsecticide into the soil andminimize the chance for exposureto people, pets and wildlife. Use arain gauge or straight-sided can toverify application of sufficient irri-gation water. Two or more irriga-tion applications may be needed ifthe soil is wet or difficult to pene-trate. Water applied too quicklymay cause run-off and pesticideloss. Irrigating the soil prior toinsecticide application, particularlywhen the soils are dry, can improvethe effectiveness of insecticides.For dry soils, apply 1⁄4 to 1⁄2 inch ofwater the day before a treatment toimprove spray penetration of thesoil and to encourage white grubsto move closer to the soil surface.This makes grubs easier to contactwith the insecticide treatment.Heavy thatch buildup can reducethe effectiveness of insecticidesprays. Thatch is the accumulationof dead plant material, such asdead grass stems, between thesoil surface and the turfgrassfoliage. Thatch layers greater than1⁄2 inch can result in greater suscep-tibility of the turf to plant diseasesand can lead to other problems.Recent research has shown thatmany pesticides bind to thatch,preventing them from reaching thesoil and reducing their effective-ness. Dethatching machines or soilaerifiers that remove small plugs ofsoil can be rented to help removethatch and enhance penetration ofthe turf by pesticides. Excessivethatch buildup is more likely tooccur with hybrid bermudagrasses,St. Augustinegrass and somezoysiagrasses. Use of mulchingmowers to recycle grass clippingsshould not cause thatch buildup inregularly mowed lawns.Environmental Considerations.Unnecessary insecticide applica-tions sometimes create more prob-lems than they solve. Pesticidescan have detrimental effects onbeneficial organisms, like earth-worms, that help decomposethatch. Most insecticides do notdiscriminate between "good" and"bad" bugs and may kill beneficialinsects that help control otherpests. Also, unnecessary pesticideapplications can increase the riskof insecticide resistance developingamong white grub and other pestpopulations. For these reasons,routine, "preventative" insecticideapplications to lawns for whitegrub control are not recommend-ed.  Heavy rainfall can wash recentlyapplied pesticides out of lawns,especially if the ground is saturatedwith water when the treatment isapplied. Avoid treating lawns justbefore a heavy rain is expected.Also try to avoid application of pes-ticides to street gutters and side-walks. Drop-type spreaders are lesslikely to scatter pesticide granulesoff of the target site than arerotary-type spreaders (Figure 4).Pesticide runoff from improperpesticide applications reduces theeffectiveness of a treatment andcan pollute above-ground andunderground water supplies.One should be aware that someinsecticides can be toxic to birdsand other wildlife. Always read andfollow label directions, includingthe precautionary statements per-taining to potential environmentalhazards. Apply only the labeledrates, avoid pesticide use nearstreams and ponds, and irrigatetreatments promptly to helpreduce the risk to non-target organ-isms, like birds. Never dispose ofleftover pesticides down sewer orstorm water drains. Such actionscan cause toxicity to fish and otheraquatic organisms.Figure 4. Drop-type spreaders allowprecise placement of insecticidegranules.Tips for Professionals■ Grubs of the southern masked chafer,Cyclocephala lurida, appear to be less destruc-tive than Phyllophaga crinita grubs. Anapproximate economic threshold for maskedchafers is 8-10 grubs per square foot. The twospecies can be distinguished by observing theraster (hair patterns) on the underside tip ofthe abdomen (see Figure 5). A 10X hand lensis sufficient to see these patterns on maturewhite grubs.  ■ Sampling for white grubs can be done using aspade or knife to cut 6-inch square sections ofturf, or by using a golf course cup cutter. Four,six-inch squares or ten, four-inch cup cuttercore samples are equivalent to one square footof turf.■ An insect that is occasionally mistaken for awhite grub is the billbug. Immature stages ofbillbugs are small, white, legless larvae com-monly found within the top few inches of soil.One species, Sphenophorus venatus, is themost common billbug collected from turf inTexas. This species can damage turfgrass, espe-cially zoysiagrasses and hybrid bermudagrass-es in the southeastern regions of the U.S., butrarely damages turfgrass in Texas.■ Merit® and Mach 2® are trade names for pro-fessional formulations of imidacloprid andhalofenozide, respectively. Merit® may pro-vide some late season grub control, but bothproducts are best used early in the season,when grubs are less than 1⁄2-inch long.  ■ Using surfactants in the spray solution mayimprove control, especially in turf with heavythatch. Trichlorfon (Dylox®) is short-lived inhigh pH (greater than 7) soils and spray solu-tions. Add buffering agents to spray solutionsto increase stability of trichlorfon sprays.Figure 5. White grub rastral patterns used in species identification are located in the anus (a) and can be observed with a 10Xhand lens. June bug larvae, Phyllophaga spp., can be recognized by their seagull-shaped anal slit ( ) and by the two parallel rowsof spines running longitudinally under the anus (b). Masked chafer larvae, Cyclocephala sp., can be recognized by their straightanal slit (–) and the random placement of spines beneath the anus (c). Scanned images courtesy Dr. Dave Shetlar, Ohio StateUniversity.⊃ ⊃a b c6/04, RevisionQuick Decision Guide for Grub TreatmentNot sure you need to treat for grubs? Want to minimize your use of pesticides for economic or environmentalreasons? Follow this quick decision guide. Remember that some treatments are effective only on small (less than1⁄2 inch-long) grubs.

White Grubs in Texas Turfgrass

http://oaktrust.library.tamu.edu/bitstream/handle/1969.1/87284/pdf_205.pdf?sequence=1&isAllowed=y

White Grubs in Texas Turfgrass

Abstract

Similar works

Full text

Available Versions

Texas A&M Repository

White Grubs in Texas Turfgrass

Abstract

Similar works

Full text

Available Versions

Texas A&amp;M Repository

Texas A&M Repository