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From the September 2016 issue of GCM magazine:

First report of carrot beetle damage to golf course turf

Traditionally a crop pest, the carrot beetle has recently been spotted on two golf courses in Kansas.

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Carrot beetles look similar to their cousins, May/June beetles and sugarcane beetles, in shape, size and color. A: Dorsal, ventral and lateral views of the carrot beetle. B: Carrot beetles have a small knob at the leading edge of a fovea (a circular, cup-like depression) just behind the head. Photos by Jim Kalisch, UNL Entomology

Jonathan L. Larson, Ph.D.; Matt S. Giese, M.S.; and Daniel A. Potter, Ph.D.

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In early June 2015, superintendents at Heritage Park Golf Course (Johnson County, Kan.) and Dub’s Dread Golf Club (Wyandotte County, Kan.) reported finding unfamiliar beetles burrowing into greens and attracting vertebrate predators that caused additional damage. Specimens of these beetles were collected by the authors and taken to Brett Ratcliffe, Ph.D., of the University of Nebraska, who identified the insects as carrot beetles, Tomarus gibbosus (Coleoptera: Scarabaeidae). A native of North America, the carrot beetle is a widely distributed species of scarab beetle (3). However, this is the first time that direct or indirect damage from T. gibbosus has been seen in any turfgrass setting.

Appearance and identifying features

As an adult, Tomarus gibbosus is robust, broadly oval and slightly wider posteriorly, with reddish brown to blackish coloration (2,3). Adults are approximately 0.5 inch (12.7 mm) long. Carrot beetles look similar to their cousins, May/June beetles (Phyllophaga species) and sugarcane beetles (Euetheola humilis), in shape, size and color. The species can be identified with the aid of a hand lens or microscope. Carrot beetles have a small knob at the leading edge of a fovea (a circular, cup-like depression) just behind the head. Carrot beetle larvae are typical C-shaped white grubs and are slightly more than 1 inch (15.4 mm) long when mature (2). The raster (underside of the last abdominal segment) bears a roughly triangular patch of short, straight hairs and lacks the zipper-like double row of spines characteristic of Phyllophaga grubs.

Feeding habits and life cycle

Historically speaking, the adult carrot beetle is a sporadic pest of corn, sunflowers, carrots, sugar beets and other crops, feeding on roots or burrowing into stalks at or just below ground level (2,4). Grubs also occasionally achieve pest status because they feed on decaying organic matter and roots of various crops and weed plants.

The carrot beetle has two distinct peaks of adult activity (2,4). Adults overwinter in soil, emerging during the first warm nights in late April and May and continuing to fly until late June. The beetles are nocturnal and fly to light sources. Mating occurs underground during May and June. Eggs are deposited in the soil from late May into July and hatch in about 11 days. Larvae are present from June until early autumn, and pupae are present from late July until early autumn.

A carrot beetle burrowing into a putting green.
Photos by John Fech

On the golf course

In June 2015, Tomarus gibbosus adults were discovered at night and in the early morning either crawling across greens and collars or partially inserted into the soil at both Heritage Park and Dub’s Dread. This burrowing left behind circular or D-shaped holes about 5/16 inch (8 mm) in diameter, tufts of turf, and small piles of soil.

When the burrows were dissected with a pocket knife, a T. gibbosus adult was often found just under the surface or, in some cases, 2 to 4 inches (5 to 10 cm) deep. Beetle activity was initially on and just inside collars, but quickly became distributed throughout an entire green. Burrows and adults were found on all greens of both courses, with more heavily infested areas showing 15 to 20 burrows and beetles per green.

Because this is the first time this interaction between turf and carrot beetle has occurred, we can only theorize why the beetles were attracted to the golf course greens. One possible explanation is that the beetles were females burrowing to lay eggs or to initiate their underground mating. The greens at Heartland Park are 70% Pennlinks creeping bentgrass (Agrostis stolonifera) and 30% annual bluegrass (Poa annua) on a high-sand root-zone mix conforming to USGA recommendations. Dub’s Dread has push-up greens with native soil and a 50:50 mix of Penncross creeping bentgrass/annual bluegrass.

Controlling adults and vertebrate damage

Not only did the beetles cause direct damage by burrowing into the green, but they attracted vertebrate predators — probably skunks and raccoons — which caused additional destruction to the greens. Digging coincided with initial beetle activity and continued until late June. Damage ranged from small, scooped-out depressions to larger patches (8 to 12 inches [20 to 30.5 cm]).

When carrot beetles burrow into putting greens, they leave behind circular or D-shaped holes as well as tufts of turf and small piles of soil.

After vertebrate damage had become apparent, lambda-cyhalothrin (Scimitar GC, Syngenta) at 0.069 pound a.i./acre (77 grams a.i./hectare) was applied on June 10, 2015. Adult beetle activity was suppressed, but vertebrate damage was noted again nine days after the Scimitar application, so carbaryl (Sevin SL, Bayer) was applied at 4 pounds a.i./acre (4.5 kilograms a.i./hectare). Dub’s Dread also applied lambda-cyhalothrin at the aforementioned rate. Although dead adults were noted, beetle activity was apparent again within two weeks. Bifenthrin (Talstar Select, FMC) was then applied 19 days after initial treatment at 0.05 pound a.i./acre (56 grams a.i./hectare). Adult activity slowed at both courses after the second insecticide application, likely as a result of the insecticide applications and the completion of the beetles’ mating/egg-laying activities.

Whether the appearance of carrot beetles on golf courses is a singular oddball occurrence or whether we can expect other courses to experience similar infestations is unknown at this time. It should be noted, though, that effective chemical control of Tomarus gibbosus on golf courses will require a different approach than typical preventive grub control methods. Most species of white grub overwinter as larvae below the freeze line of the soil (including chafers and Japanese beetles). Tomarus gibbosus, though, spends most of its life as an adult, as does the sugarcane beetle, which is a sporadic pest of turf in the southeastern United States. The protocols used for managing the sugarcane beetle — for example, targeting overwintered adults with a pyrethroid insecticide as soon as the beetles are observed crawling on greens or flying to lights in spring (1) — may therefore also be effective for controlling carrot beetles.

To date, there have been no other reports of this beetle invading turf, and no further issues have arisen at the two Kansas courses. Anyone who finds either beetles or damage that matches the descriptions here should report the information to their local university extension office.

Damage caused by a vertebrate predator (probably a skunk) pursuing a carrot beetle on a putting green.

Acknowledgments

The authors would like to thank the two golf courses for welcoming us to their facilities, as well as John Fech of the University of Nebraska-Lincoln Extension for help with photography.

The information in this paper was originally published as “First report of carrot beetle (Tomarus gibbosus) damage to golf course turf” by Jonathan L. Larson, Matt S. Giese and Daniel Potter in Crop, Forage and Turfgrass Management doi: 1010.2134/cftm2015.0188. Copyright 2016 American Society of Agronomy and Crop Science Society of America, Madison, Wis.

Literature cited

1. Billeisen, T.L., and R.L. Brandenburg. 2014. Biology and management of the sugarcane beetle (Coleoptera: Scarabaeidae) in turfgrass. Journal of Integrated Pest Management 5:2014. (doi:http://dx.doi.org/10.1603/IPM14008). Accessed July 22, 2016.
2. Hayes, W.P. 1917. Studies on the life-history of Ligyrus gibbosus Deg. (Coleoptera). Journal of Economic Entomology 10:253-261.
3. Ratcliffe, B.C., and M.J. Paulsen. 2008. The Scarabaeoid beetles of Nebraska. Bulletin of the University Nebraska State Museum 22:1-570.
4. Rogers, C.E. 1974. Bionomics of the carrot beetle in the Texas rolling plains. Environmental Entomology 3:969-974.

Jonathan L. Larson is an extension entomologist for the University of Nebraska-Lincoln Extension and serves the Omaha, Neb., metro area. Matt S. Giese is the Midwest technical field manager for Syngenta Turf & Landscape in Kansas City, Kan. Daniel A. Potter is a professor in the Department of Entomology at the University of Kentucky, Lexington.