White grubs are among the most common pests found on golf courses, sports fields and even home lawns, yet they often can be some of the most challenging nuisances to control for superintendents, sports field managers and lawn care operators.
Left untreated, white grubs, the larva of many common beetle species, chew on the roots of turfgrass and can wipe out wide areas in a short amount of time. Many researchers agree the best way to mitigate white grub damage is through preventive pesticide applications to catch emerging larvae before they can begin feeding.
White grubs found in turf are the larval stage of several common beetle species that include Japanese beetle, Asiatic garden beetle, European chafers, masked chafers, Oriental beetles, green June beetle, May/June beetles and black turfgrass ataenius.
The life cycle of annual white grubs, which includes many of the beetle and chafer species, is well known and predictable. Adults emerge from the soil in May or June, mate and lay eggs in midsummer a few inches below the surface and hatch in about two weeks, according to retired University of Kentucky entomologist and 2010 USGA Green Section recipient Dan Potter, Ph.D.
Early and late-instar larvae feed on the roots of turf from through September, but damage can appear any time from August through November. By autumn they begin descending deeper into the soil where they overwinter. In spring, mature larvae move higher into the profile where they make the transition to pupa then adult and emerge from the soil to lay their eggs, starting the process all over again.
Although prevention with early season pesticide applications often can provide control throughout the season, even the best plans often require late-season curative applications.
Root damage is not the only threat in areas with late-season grub populations. Such areas also are open to secondary damage from predators such as birds, raccoons and skunks looking for an easy meal.
Early season preventive applications of neonicotinoids (clothianidin, imidacloprid, thiamethoxam) and diamides (chlorantraniliprole, cyantraniliprole, tetraniliprole), according to research at Purdue University.
While fat and sassy late-season grubs are a favorite of predators, they can be difficult to control.
Insecticides used for curative control have a shorter residual effectiveness than neonicotinoids or diamides. Grubs are still vulnerable to treatment in late August and September but as they grow larger, they become more difficult to control.
According to researchers at Oklahoma State, insecticides recommended for curative control include trichlorfon, carbaryl and clothianidin.
Turf should be watered in before treatment to bring grubs closer to the root zone where they will be more susceptible to the insecticide. After application, turf should be lightly irrigated to move the insecticide into the root zone where white grubs reside. Dethatching a before treatment can also help move product to where it is needed.
