GREEN JUNE BEETLE GRUBS
CAUTION: This information was developed for North Carolina and may not apply to other areas.
Reports of green June beetle (aka fig beetle) grubs as a problem in pastures have been increasing across the state. Most of these pastures have a history of applying organic fertilizers, especially poultry litter, manure or sludge. If you have seen many adults, and have high organically fertilized pastures, you may be at risk for GJB damage. Green June beetle grubs feed on organic matter in the root zone. Most damage is thought to be a result of heavy tunnelling and dislodging of roots. Cattle and other grazing animals may uproot poorly anchored plants. Separation of roots with soil contact especially stresses the plants during periods of drought., resulting in brown and dying patches. The grubs of green June beetle have an unusual behavior. At night, large larvae may leave the soil and crawl along the surface on their backs. Holes with small earthen turrets about the diameter of a finger are sometimes evident in late spring.
Adults are metallic green, about one inch long, and are low, slow, morning flyers, often making a dull buzz as they go. Sometimes adults are noticed around overripe fruit, if it is nearby, and may be a nuisance there. Green June beetle adults are attracted to sandy and sandy loam soils high in organic matter that makes up a large part of the grub's diet.
In pasture, examine
sod about 1 sq. foot and four inches deep for grubs. There is no precise threshold,
but if 4 or more larvae per square foot of sod are detected, treatment may be
considered if damage is being noticed and if winter overseeding is to take place.
These large grubs are often found under hay bales left in the field, near manure
piles, and in thick organic turf. Also examine areas for dark blue scolyiid
wasp activity, pulverized soil, and broadleaf weed encroachment. Pulverized
soil is a typical sign of green June beetles in pastures. Notice whether broad-leaved
weeds have invaded the infested area. Weeds quickly colonize the bare patches
created where a plant dies or is uprooted. Birds and other animals may dig grubs
out of turf and pastures causing additional damage.
Green June beetles have one generation each year. The grubs overwinter in the soil. They may become active during warm winter days. Fresh mounds of trails of pulverized soil indicate fresh grub activity. Grub activity increases as the spring weather becomes consistently warmer.
JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC
Grubs pupate in cells in the soil during late April and May and remain in the pupal stage for 2 or 3 weeks. Newly emerged adults remain in the soil for an additional week or two. In most years, green June beetles leave the soil beginning in late May and continue through early August. Peak flights usually occur from June through July.
After mating, the female green June beetle flies close to the turf or grass surface, selects a site (preferably moist, organic soil), and digs several inches into the soil. The female beetle constructs a walnut-sized ball of soil in which she lays 10 to 30 eggs. Eggs are nearly round, about 1/16 inch in diameter. Each female may lay as many as 75 eggs during a 2-week period. Eggs hatch in 2 weeks. Newly hatched grubs are about 3/8 inch long. Young grubs begin to tunnel through the soil in search of food (organic matter). They typically come to the surface to feed.
In turf, the grubs usually leave small mounds of soil around the mouth of each tunnel. By August, grubs are large enough for mounds to be seen on short mowed turf and by mid-September on taller grass. In pastures, grubs leave trails of pulverized soil as they tunnel near the surface.
A large, dark-colored wasp, Scolia dubia, is often seen flying low over grassy areas infested with green June beetle grubs (most often in August). This bluewinged wasp attacks green June beetle grubs and is considered beneficial. This wasp is blue-black in color, and slightly longer than an inch. The rear half of the abdomen is brown and fuzzy, with two large yellow spots. The female wasp goes down into the soil to find green June beetle grubs. When she finds one, she stings it, causing it to be paralyzed, then lays her eggs. The wasp larvae hatch and consume the green June beetle grub.
Chemical treatment may be hard to justify in pastures, but if needed, is most effective in September. Timing may vary, so treat infested areas based on scouting. Sevin (carbaryl) is the normal chemical recommendation. Be sure to use adequate water and observe the 14-day grazing interval. The best time of day to treat is in late afternoon when temperatures are above 70 degrees F. Entire fields may not need treatment so scout for the infested portions of a field.
For some additional information and photos, visit the Auburn
publications by K.L. Flanders at
Recommendations of specific chemicals are based upon information on the manufacturer's label and performance in a limited number of trials. Because environmental conditions and methods of application by growers may vary widely, performance of the chemical will not always conform to the safety and pest control standards indicated by experimental data.
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 the North Carolina Cooperative Extension Service nor 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 and examine a current product label before applying any chemical.
For assistance, contact your county North Carolina Cooperative Extension Service agent.
For assistance with a specific problem, contact your local North Carolina Cooperative Extension Service.
Published by North Carolina Cooperative Extension ServiceDistributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.
ENT/for-02 May, 2003
Web page last reviewed January, 2011 by the webperson.