Best Management Practices for White Grub Control Impact of White Grubs The larval stages of several beetle species can be quite damaging to cool season turf athletic fields. These larvae, commonly called white grubs, are one of the most destructive insect pests on high maintenance turf in the United States. Because grubs damage turf by feeding on roots, the plant’s ability to absorb moisture and nutrients, essential for growth and survival, are significantly depleted. Due to their geographical distribution and potential for large populations, the likelihood for large areas of athletic fields to be affected is great. Grub Life Cycles Several white grub species, such as masked chafers, Japanese beetles, and green June beetles, have similar life cycles that take one year to complete. Adult beetles emerge, mate, and lay eggs in midsummer, mainly from late June until early August. Eggs are laid a few inches below the surface and hatch in about two weeks. D. Shetlar, OSU Northern Masked Chafer Life Stages Egg 1st 2nd Instar larva 3rd Pupa Adult The tiny (1/8-inch long) first-instar grubs (those just emerged from the egg) grow quickly, feeding on fine roots and organic matter. As they grow, the grubs molt (shed their skin) twice, the two post-molt stages being sequentially referred to as second and third instars. Most grubs are third instars by late summer or early fall. In October or November, when soil temperatures begin to cool, the grubs cease feeding and move deeper into the soil, where they spend the winter. They return to the root zone and resume feeding early the following spring. When mature (typically in late May), the grubs again move deeper, form an earthen cell, and transform into pupae. The adult beetles emerge a few weeks later, in June and July, to complete the one-year cycle. Not all species have an annual life cycle. May beetles take two to three years to complete their cycle, while the black turfgrass ataenius has two generations per year. The adults are active in the spring (late March to early May) and again in midsummer. Thatch Management For best results with any grub insecticide, remove dead grass and thatch before treatment, which allows better penetration of the spray or granules and reduces the amount of insecticide bound by surface debris. White grubs are especially hard to control in turf with a heavy thatch layer, because most of the insecticide can be tied up in the organic matter and fails to reach the root zone. If the thatch layer is more than 1/2-inch thick, consider removing it manually or with a dethatching machine before applying a grub treatment. Application Timing Preventive treatment with Meridian® insecticide Preventive control requires the use of insecticides with long residual activity in soil, and turfgrass managers must use a different timing than they would for curative treatments. • Applied as early as mid-May, insecticides typically have sufficient soil persistence to control young grubs hatching from eggs in July or early August. • However, the optimum period for application is mid-June to mid-July, during the month or so preceding egg hatch until the time when very young grubs are present. Meridian Insecticide Best Management Practices Recommendation Preventive Application Timing Up to 45 days before peak adult flight of species targeted (Mid-June–mid/late July) Preventive Application Rate 17 oz/Acre Up to 7 days after application Preventive Watering-in Requirements Curative treatment with Meridian insecticide With curative control, treatment is applied in late summer, after the eggs have hatched and grubs are present. • The best time to apply curative grub insecticide is when grubs are still small and their feeding damage is relatively light. Early symptoms include gradual thinning, yellowing, and weakening of the grass stand followed by the appearance of scattered, irregular dead patches. • As the grubs grow larger, they become progressively harder to control, and damage to the turf already may be severe. • By September, in response to cooler soil temperatures, some grubs already may be moving downward and out of the treatment zone. To avoid these control challenges, many turf managers are turning to a preventive strategy made possible by newer, longer-lasting insecticides. Meridian Insecticide Best Management Practices Recommendation Curative Application Timing Egg hatch to 2nd instar grub stage (late July–August) Curative Application Rate 17 oz/Acre Curative Watering-in Requirements Within 24 hours of application Meridian White Grub (larvae) Spectrum Aphodius spp. Black Turfgrass Ataenius Japanese Beetle Asiatic Garden Beetle Chafers: European, Southern, Northern May and June Beetle Billbugs Green June Beetle Oriental Beetle The one online information source with the innovative services and technologies to help you manage your turf and ornamental needs. www.greencastonline.com Reference: Potter, M.F. and Potter, D.A. Controlling White Grubs in Turfgrass. University of Kentucky, 2000. 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