Alfalfa growers in New Mexico are facing an outbreak of black cowpea aphids.
First reported in late March, the infestation encompasses several counties in the central, eastern and southern parts of the state. Several thousand acres of alfalfa have been damaged.
Cowpea aphids have damaged alfalfa in California and several other states the past two years, but this is the first reported outbreak in New Mexico.
The aphid has been in the state a long time, but has never been a serious pest on alfalfa, says Mike English, New Mexico State University entomologist.
"In the past two years, it has changed its habits and has decided it really likes alfalfa," says English. "Now it’s become a virulent pest that’s taking off with a vengeance around the state."
Several insects, including bigeyed bugs, damsel bugs, lacewings and lady beetles, feed on cowpea aphids. As populations of natural predators increase this summer, the aphid infestation may be reduced, he says.
But pesticides are the best means of control – several work well on cowpea aphids. Flood irrigation seems to substantially reduce numbers, too.
The most important step is for growers to monitor their fields throughout the growing season, according to English. Stop the bugs early, before they have a chance to spread, he advises.
"All New Mexico growers need to be aware that this thing has hit the state, and they have to get out there in their fields and look for them," he says. "Farmers need to get down on their hands and knees and scout for those critters."