WOOSTER, Ohio -- A wheat pest that has been off the radar screen for the past three decades in Ohio may be making a comeback.
Cereal leaf beetle has been causing serious damage to some Ohio wheat fields over the past two years to such an extent that Ohio State University entomologists are revisiting research that hasn't been conducted on the insect since the 1970s.
"Cereal leaf beetle was a serious problem back in the 1960s and early 1970s, but through research, parasitoids (parasitic wasps, for example) were introduced that controlled the insects. When I came on board in the 1970s, nobody was paying attention to it anymore and that's been the case for a long time," said Ron Hammond, an OSU Extension entomologist with the Ohio Agricultural Research and Development Center. "But for the past two years, something has happened and suddenly either the beetle is doing very well or the parasitoids have disappeared or are no longer being effective."
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.
"Some of our wheat breeders this year have had to treat their wheat trials with insecticides and some organic wheat fields have just been devastated," said Hammond.
Entomologists are unsure as to why the cereal leaf beetle, effectively controlled for so many years, 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.
"I don't think anyone will argue that our winters the past couple of years have been more mild than normal," said Hammond. "We are not sure what's going on, but it may be time that growers start paying attention to this insect and any feeding damage that it may be causing."
There is one generation of adults per year that 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.