WOOSTER, Ohio -- The cereal leaf beetle, a wheat pest of bygone days, is becoming more numerous again in Ohio, and some cereal grain growers are seeing feeding damage to their crop this season.
Ron Hammond, an Ohio State University entomologist with the Ohio Agricultural Research and Development Center, said that localized wheat fields in parts of northeast and central Ohio have been a target for cereal leaf beetle populations, and how widespread the problem is remains to be seen.
"In late April and early May, we started hearing reports of a lot more adult cereal leaf beetles than we've seen in the past, and some fields are already being sprayed," said Hammond, who also holds an OSU Extension appointment. "We are recommending that wheat growers check their fields to make sure something unexpected isn't happening."
The cereal leaf beetle, once a serious problem in Ohio, was effectively controlled by parasitoids (parasitic wasps, for example) for over three decades. However, for the past three seasons, entomologists have noticed that the beetle is re-establishing itself.
"We are not sure what's happening, if the beneficials are failing us or if there is something else going on," said Hammond. "It's disconcerting that now problems seem to be popping up after we went for so many years without any problems."
The larva of the cereal leaf beetle causes the most damage to the wheat crop, attacking the plant's flag leaf soon after emerging in the spring. Just two larvae per flag leaf stem can be devastating, since the flag leaf is the center of grain fill and ultimately controls yield.
"The cereal leaf beetle just scrapes off leaf tissue and strips that leaf of all its chlorophyll," said Hammond. An infestation averaging over two larvae per stem can result in economic losses.
One generation of adults per year lays eggs in the spring on grasses, such as wheat and oats. The emerging larvae, one-quarter to three-quarters of an inch in size, appear as small black slugs. Evaluation of an infested field, which can take on a frosted appearance, should include sampling of 30 or more plants to determine the number of larvae per stem. An average of two or more larvae per stem is the economic threshold and warrants insecticide use.
Organic cereal grain fields are the most at risk from cereal leaf beetle damage.
"Organic growers who experience problems with cereal leaf beetle on wheat and other cereal grain crops should be aware that they have an organically approved product, Entrust, made by Dow they can use," said Hammond. "Entrust contains spinosad, which is produced through the fermentation of living organisms."
Entomologists are unsure as to why the cereal leaf beetle is again becoming a problem. Some speculation points to increasingly mild Ohio winters. In the past, treatments have been warranted when adversely mild winters have affected natural control.