Developing Cost Effective Control Options for White Grubs

White grubs, the larvae of scarab beetles, are one of the most important economic pests of turfgrass throughout the United States. White grubs species such as Japanese beetle, oriental beetle, northern and southern masked chafers, May or June beetles, and green June beetles are known to occur in North Carolina. White grubs infest both cool and warm-season grasses and feed on the roots just below the thatch. Early signs of the grubs may include thinning and yellowing of turf followed by irregular dead patches. Other signs of the grubs may include seeing predators of the grubs such as skunks, raccoons, moles, and birds digging in the turf to find a juicy snack.

The majority of white grub species undergo a one-year (annual) life cycle. Adult beetles emerge, mate, and lay eggs (30 to 40 per female) from June to mid-August. The first instar emerges in roughly 2 weeks and immediately begins feeding on roots and organic matter.  Grubs feed until the first frost and then move deeper into the soil to overwinter. In the spring, when the soil begins to warm up, they move back into the root zone to feed. The adult beetle will then emerge in a few weeks completing the one year life cycle.

Turfgrass managers currently have two options when managing white grubs: preventative or curative treatments. Preventative insecticides such as Merit (imidacloprid), Arena (clothianidin), Mach II (halofenozide) are applied slightly before, during, or after egg hatch (June to mid-August). These insecticides have a longer residual (~90 days) which gives them a wide window of application. These products are applied at low rates and are less toxic to people, non-target organisms, and the environment as compared to older chemicals. Curative insecticides such as Dylox (trichlorofon) and Sevin (carbaryl) are fast acting products used for spot treating. Both treatments are targeted for after egg hatch but while grubs are still small. Correct timing may be difficult due to short residual activity. Accurate identification of the target species and timing of treatment is vital for effective control for all management options mentioned. Also, post-treatment irrigation is required to move insecticides through the thatch to reach grubs.

Research is currently being conducted at NCSU to determine the variety of species of white grubs damaging turfgrass throughout North Carolina. The research is being conducted by Callie Prater and Dr. Rick Brandenburg. I am helping Callie conduct research here in Western North Carolina by collecting beetles from pheromone and black light traps. Callie and I placed traps at Grove Park Inn Golf Course, Biltmore Forest Golf Course, and Crowfields Retirement Community where I collect trapped beetles weekly and mail them to NCSU. Callie then analyzes the data to determine species abundance and flight patterns. Callie and Cliff Ruth, Henderson County Extension Agent, placed pheromone and black light traps in Henderson County as well.

Over the next two years Callie and Dr. Brandenburg will continue to refine our understanding of the different white grub species, individual species distribution, as well as their life cycles. Understanding the white grub species further will allow for the evaluation of biological control agents such as nematodes and fungi that attack white grubs. This will also allow for further evaluation of cultural practices such as the use of humic acid, sulfur, and UV reflectance sprays. Early observations indicate the application of UV reflectance sprays may act to camouflage the turf from female Japanese beetles searching for lush green areas of turf in which to lay her eggs.

The goal of the research is to develop a cost effective management program incorporating both conventional insecticides and ‘non-traditional’ control strategies.

Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by NCSU, NCA&T State University or NC Cooperative Extension or discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage regulations and examine a current product label before applying any chemical.  For assistance, contact an agent of NC Cooperative Extension.