Source: Ron Hammond, Ohio State University Extension
Economic populations of cereal leaf beetle are being found on Ohio wheat. This could be the year the pest, making a comeback in Ohio, causes widespread problems, says Ohio State University Extension entomologist Ron Hammond.
"We are becoming aware of the populations of cereal leaf beetle, both in the southern and central parts of the state, but there is also potential for outbreaks in the northern counties," said Hammond, who also holds an appointment with the Ohio Agricultural Research and Development Center. "This could be the year the pest really breaks out and causes widespread problems."
The cereal leaf beetle is a wheat pest of bygone days — controlled effectively by parasitoids (parasitic wasps, for example) for over three decades. However, for the past several 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.
Economic threshold is one to two larvae per stem or flag leaf.
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. This appearance comes from their own feces adhering to their bodies. Evaluation of an infested field, which can take on a frosted appearance if injury is severe, should include sampling of 30 or more plants to determine the number of larvae per stem. An average of one to two or more larvae per stem is the economic threshold and warrants insecticide use.
Organic cereal grain fields are also 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.
For more information on cereal leaf beetle and a list of labeled insecticides, log on to http://ohioline.osu.edu/ent-fact/pdf/0038.pdf and http://entomology.osu.edu/ag/images/Small_Grains_CLB.pdf.