Wooster, Ohio
June 21, 2007
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.
 |
|
Beetle larvae |
“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.
 |
|
Beetle damage |
“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. |
|
