Grubs In Manure Applied Pasture
CAUTION: This information was developed for North Carolina and may not apply to other areas.
Reports of white beetle grubs in pastures are not uncommon across the state. Most of these pastures have a history of applying organic fertilizers, especially poultry litter, dairy manure or sludge. However, the presence of grubs in a pasture does not automatically mean a problem. Identification of the grubs is important. Often, more than one species of grub is present at the same time. Detailed species identification can be difficult in some cases and is often determined by hair patterns on the tail section of the grub (raster patterns). Problems sometimes arise later as the field is planted into corn or another crop. One point to remember is that in most cases these grubs are doing what we want, that is breaking down the manure and organic matter. There is a limit as to how much manure a field can handle, however.
Green June Beetle Grubs- (Cotinis nitida)
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 are the only larvae that 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. They have a one year life cycle.
Manure Grubs- (Aphodius sp.)
These
dung beetle grubs are in the genus Aphodius and are common in heavily
manured fields. They are rarely responsible for stand loss since they mostly
feed on the manure in the soil. The small grubs are about the size of
a slightly flattened B-B with red heads. A
University
of Sydney study claims
control of certain grubs in pasture using a strain of Mettarhizium fungus,
but there has been no such study in the U.S.
Japanese Beetle Grubs- (Popillia japonica)
Larvae
hatch in mid-late summer and feed through the fall,
then move lower in the soil as winter temperatures drop. The grubs move back
toward the soil surface in the spring and feed on organic matter and root hairs.
Too much root feeding can cause problems with water and mineral uptake especially
during drought stress and on young plants. When feeding is completed, the grubs
pupate, and adults emerge
in early summer. Egg
laying follows shortly after to complete the one year life
cycle.
Chafer Grubs- (Cyclocephala sp.)
Many
chafers are in the genus Cyclocephala and may appear more similar
to Japanese beetles in shape than the other scarab beetles. Adults tend
to be more plainly colored. They are typically not as abundant nor considered
as damaging as Japanese beetle grubs, by themselves. The grubs in this one
year life cycle lack the zipper raster
pattern.
White Grubs- (Phyllophaga sp.)
May
and June beetles belong
to the genus Phyllophaga. There are several
species and they may occur together. This group has the typical "zipper"
raster pattern. This is the group often referred to as "true white grubs".
Life cycles are typically three years. A.M.
Dix & C.R. Carol showed that Phyllophaga beetles had a strong preference
for buried corn stalks and fresh poultry manure over old manure and live corn
roots. There is insufficient evidence of treatable damage to pasture
by white grubs and there is no threshold.
There is little that can be done in pastures for most of these grubs. There are no soil insecticides labeled in pastures that would control grubs when in the soil. However, since green June beetle grubs come to the surface, soil surface applications of carbaryl (Sevin) can be useful in their case. Chemical treatment may be hard to justify, but if needed, is most effective in September. Timing may vary, so treat infested areas based on scouting. 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.
Useful Links
Green
June Beetle Insect Note
Japanese Beetle Insect Note
White Grubs in Turf
Auburn
publication by K.L. Flanders
http://www.aces.edu/pubs/docs/A/ANR-0991
True
White Grubs and Early Season Corn in Iowa
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 with a specific problem, contact your local North Carolina Cooperative Extension Service.
Published by North Carolina Cooperative Extension Service
Distributed 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.
Web page last reviewed January, 2011 by the webperson.
