Growers Feel Blue over Aphid Damage, Loss of Greenbacks

Farmers can certainly get worked up when talk turns to bugs and bucks.

This certainly was the case last Friday while attending an alfalfa field day in Dos Palos last Friday led by Dr. Pete Goodell of UC Integrated Pest Management and UC Extension entomologist Larry Godfrey.

The pea aphid can be mistaken for the blue alfalfa aphid.
- Photo by Kansas State University

The buzz among alfalfa growers in the Central Valley this season has centered on the pesky blue alfalfa aphid, which feed on alfalfa stems and can lead to wilting and stunted growth. These deep green-blue invasive bugs – which can be confused with the pea aphid – were particularly troublesome this spring.

Indeed, Pete and our alfalfa-cotton field scout Carlos Silva saw the problem first hand while touring local alfalfa fields recently. This field looked like the alfalfa had just been cut for the first time this season. The only problem: the first cutting came about a month earlier. That spells revenue loss.

Here are examples of damage by the blue alfalfa aphid.
- Photo by Oklahoma State University

According to Larry, the blue alfalfa aphid was first found in alfalfa near Bakersfield in 1974. The following year, this invasive pest from eastern and southwester Asia was discovered throughout Southern California. Today, this aphid can be found as far east as Kansas and Oklahoma.

In the San Joaquin Valley, pest control advisors indicated during the field day that treatments weren’t totally effective this spring. So far, there are no definitive answers to the treatment issue or the root of the blue alfalfa aphid outbreak.

On the bright side, Carlos says he has recorded low counts of blue alfalfa aphids during his field sweeps. The spate of hot weather could be an ally for the rest of this year. These pests thrive in 60 degree weather. When the thermometer reaches 75 to 80 degrees the blue alfalfa aphid population decreases quickly. That’s one good thing about these 90-degree days. Although temperatures dipped into the high 70s the past few days, weather forecasts say the weather should quickly head back into the 80s. We can probably say wait till next year for these aphids.

In the meantime, growers are poised to do the second alfalfa cutting of the season. One farmer, in fact, already wrapped up his second harvest.

On the cotton front, the young plants are basking in the hot sunshine and growing rapidly.  Cotton stand development is good. The seedlings are growing nicely with some plants reaching first true leaf, which is the time the plants start developing squares.

Spider mites are pests to cotton.
- Photos by UC IPM

Watch for the western flower thrip.

Growers should monitor for whiteflies.

Cotton growers need to keep an eye out on thrips, spider mites and whiteflies.  So far, there are no major pest problems to be worried about at this time.  Keeping check back here for field updates throughout the season.