White Grubs in Texas Turfgrass Michael Merchant, Stephen Biles and Dale Mott*

E-211 6/04 White Grubs in Texas Turfgrass Michael Merchant, Stephen Biles and Dale Mott* White grubs are the larval stage of The most important turfgrass- grass include Cyclocephala pasade- insects commonly known as May infesting white grubs in Texas are nae and Phyllophaga submucida. or June beetles (or Junebugs). Texas the June beetle, Phyllophaga crinita has almost 100 species of these bee- (Figure 2), and the southern Another interesting kind of white tles, most of which do not cause masked chafer, Cyclocephala lurida. grub is the green June beetle, significant economic damage to Warm season grasses like bermuda- Cotinus nitida. These rather large crops or horticultural plantings. A grass, zoysiagrass, grubs feed primarily on decaying few species, however, commonly St. Augustinegrass organic matter and normally do damage turfgrass and other culti- and buffalograss not injure turf; however, turf can vated plants. are attacked readily be damaged by their burrowing by both types of activity. Larvae are especially com- White grubs, sometimes referred to white grubs, with mon underneath fruit trees, in as grubworms, injure turf by feed- most lawn damage compost piles and in soils with ing on roots and other under- occurring during sum- high organic content, such as may ground plant parts. Damaged areas mer and fall months. be found in heavily mulched gar- within lawns lose vigor and turn dens and flower beds. Daytime Figure 2. Adult white grubs, often brown (Figure 1). Severely dam- resting places of green June beetle aged turf can be lifted by hand or called May or June beetles, are com- larvae can often be found near rolled up from the ground like a monly attracted to lights at night. such sites and are marked by small carpet. mounds of soil on the lawn sur- Cool season grasses such as the fes- face. The larvae have a curious cues, bluegrass and ryegrass are habit of crawling on their backs also susceptible to the June beetle across the soil surface to move and southern masked chafer, from one site to another. Adults of though such grasses tend to be the green June beetle are velvet- attacked more frequently by a green on the top, metallic green May beetle, Phyllophaga congrua. below and approximately one inch Damage from May beetles often long. Adults fly during the day and appears in the spring and early feed on over-ripe fruit. summe r, before injury from other Figure 1. Golf course fairway dam- white grubs becomes evident. *Extension Urban Entomologist and Extension aged by white grubs. Other white grub species occasion- Agents-IPM, respectively, for Texas Cooperative ally recorded as pests in Texas turf- Extension, The Texas A&M University System. adult flight periods may not sub- When cool weather arrives, white Life Cycle stantially reduce subsequent white grubs become dormant until the Most turfgrass-feeding white grubs grub damage. Heavy white grub following spring. During this dor- in Texas, such as the June beetle infestations often can be found in mant period white grubs do little and southern masked chafer, areas with little or no outdoor or no feeding and cause little dam- require 1 year to complete their life lighting. age. Occasionally white grubs will cycle (a 2-year cycle is suspected in be found in turfgrass areas that fail After mating, female beetles dig 2 a portion of the grub populations to green up in the spring; however, to 5 inches into the soil to lay eggs. in north Texas). The May beetle, the damage is primarily the result Each female can lay up to 30 to 40 Phyllophaga congrua, requires 2 of feeding that occurred the previ- eggs, which hatch in approximate- years to develop. For simplicity, the ous fall. Spring and winter treat- ly two weeks. following discussion will be limited ments for white grubs with 1-year to species with 1-year life cycles. life cycles generally are ineffective Larva. White grub larvae are in preventing turf damage. Once a year, in late spring or creamy white and C-shaped, with summer, adult beetles emerge from three pairs of legs (Figure 3). After Pupa. The pupal stage follows the the soil to mate. Mated females hatching, the white grub passes third-instar and is the life stage then return to the soil to lay eggs. through three larval life-stages, or during which the white grub trans- Within about two weeks the eggs instars. These instars are similar in forms, or metamorphoses, into an hatch into small white grubs that appearance, except for their size. adult beetle. The pupal stage does feed on grass roots. The pupa, or First- and second-instars each not consume food and does not intermediate stage between the require about 3 weeks to develop to move through the soil. This life larva and the adult, occurs the fol- the next life-stage. The third-instar stage occurs during the spring and lowing spring and is the last imma- actively feeds until cool weather lasts approximately 3 weeks. Pupae ture phase of the insect's develop- arrives. Third-instar larvae are can be found in small earthen cells ment cycle. Adults subsequently responsible for most turfgrass dam- three to six inches below the soil 1 emerge from the pupal stage when age due to their large size ( ⁄ 2 to 1 surface. White grub treatments environmental conditions are inch-long) and voracious appetites. applied during the pupal life stage favorable in early- to mid-summer. Feeding by large numbers of third- are both ineffective and unneces- Most damage from white grubs instar white grubs can quickly sary. occurs during mid-summer to destroy turfgrass root systems, pre- early-fall when the larger larvae are venting efficient uptake of food actively feeding. and water. Damaged turf does not grow vigorously and is extremely Managing White Grubs Adult. The adult stage of the susceptible to drying out, especial- Knowing when you have a prob- various white grub species are ly in hot weather. lem. White grub damage can be 1 5 detected by the presence of irregu- heavy-bodied beetles, ⁄ 2 to ⁄ 8 inch long, brown, with long, spindly lar-shaped areas of weakened or legs (Figure 2). The June beetle and dying grass in the lawn. Less- southern masked chafer emerge severely damaged turf lacks vigor from the soil and fly at night, usu- and is more vulnerable to invasion ally after a significant rainfall or by weeds. Depending on location irrigation. Flight periods may last within the state, damage may for several weeks, during which appear any time between the time mating and egg-laying occur. months of June and October. During flights, large numbers of Turfgrass damaged by white grubs adult beetles, primarily males, may has a reduced root system and is be attracted to lighted windows or easily pulled from the soil. Grubs should be readily found in the top other lights at night. Females, Figure 3. Turfgrass-infesting white few inches of soil, in the turfgrass being less active fliers, usually are grub larvae feeding on grass roots. less common around lighted areas root zone. Turfgrass usually recov- Grubs are most damaging when they ers from white grub damage by fall than are males. For this reason, 1 reach a length of ⁄2- to 1-inch. turning off outdoor lights during or the following spring. At least one turfgrass disease, ing insects. These microscopic must be applied early enough to 1 Take-all Patch, can sometimes be worms can be purchased in stores kill the smaller (less than ⁄ 2-inch- mistaken for white grub damage. or through garden supply catalogs. long) larvae. Once white grubs Take-all Patch occurs most fre- Commercial nematode products reach the third-instar life stage, quently in spring and early sum- are usually designed to be mixed they are more difficult to control mer and can be distinguished by with water and applied to lawns with the new products. the rotted appearance of the roots. using a hose-end or hand-held In contrast with white grub dam- sprayer. Recent research shows that The insecticides imidacloprid and age, dead spots caused by Take-all under good conditions commer- halofenozide are used most today Patch may persist into the summer cially-available nematodes can for white grub control. Imidaclo- months. reduce white grub populations by prid is most effective against small- 50% or more. and medium-sized grubs but may 1 Some Texas lawns never suffer kill some grubs larger than ⁄ 2 inch white grub damage, while others Nematodes must be supplied with long. Imidacloprid trade names are damaged year after year. If your adequate moisture to help them include Merit®, Bayer Advanced lawn consistently dies out in move down into the soil where Lawn™ Season Long Grub Control 1 patches during late summer and if grubs are feeding. At least ⁄ 4 inch and Scott's® Grub-Ex®. The lethal you can verify that white grubs are of water should be applied before, effects of the insect growth regula- 1 the culprits, you may benefit from and another ⁄ 4 inch of water tor halofenozide are limited to a preventative treatment. On the applied just after, nematodes are early white grub life stages. other hand, if you want to mini- sprayed on the lawn. These worms Halofenozide is ineffective if mize your use of insecticides and pose no threat to humans or land- applied too late, after grubs have don’t mind sampling for white scape plants and are an environ- reached the third-instar life stage. grubs, follow the quick decision mentally sound alternative for Halofenozide trade names include guide on page 6.

Load more