The cowpea aphid has become a problem in alfalfa in Tulare County, Calif., within the past year.

When conditions are right, high populations of the black shiny aphid develop to severely stunt plants and result in high levels of honeydew and the subsequent sooty mold on plants.

The aphid reached treatable levels in January as well as in July in Tulare County, according to Carol Frate, county farm advisor. High populations were found in western Fresno County in November and December of last year, she said.

"It is highly unusual for a species of aphid to thrive under such different temperature regimes," Frate observed. "As a consequence, there are no times of the year when we can say it is safe not to be concerned about the aphid."

Frate said the one exception is when it is rainy and foggy as there are fungi that parasitize aphids under those environmental conditions. "But if this fall and winter are dry and there is little fog, keeping an eye out for this aphid would be the safe thing to do," Frate said.