2013 Highlights: UC IPM Annual Report

UC responds to blue alfalfa aphid outbreak

blue alfalfa aphids from an alfalfa field, seen in a sweep net.

The blue alfalfa aphid, shown here, looks similar to the pea aphid, but requires quicker management to prevent alfalfa damage. (Photo by P. Goodell.)


  • Outbreaks of the blue alfalfa aphid, an aphid not seen in many years, were reported throughout the state in 2013.
  • A toxin injected by the aphid when it feeds on alfalfa causes stunting, reducing alfalfa yield and quality.
  • The aphid can be managed according to the Alfalfa Pest Management Guidelines.

In 2013, the blue alfalfa aphid, an aphid species that hadnít been seen in many years, reared its head across a wide area of California alfalfa. The pest appeared in high numbers and required extra insecticide applications for control.

The blue alfalfa aphid injects a toxin that stunts alfalfa growth, so yield and quality are reduced during the next cutting. This destructive pest was reported from Imperial and Los Angeles counties to the mid-San Joaquin Valley.

Pest control advisors (PCAs) in Kern County began noticing this pest in early March, then several weeks later PCAs reported outbreaks in Merced County. IPM Advisor Pete Goodell quickly organized several meetings with UCCE specialists and advisors and highly experienced PCAs to spread the word, discuss the situation, and gather and review information to understand the cause of the outbreak and determine the best management approach.

The team suggests that dry winter weather may have led to the recent blue alfalfa aphid problem. They found that no particular alfalfa variety was damaged more than others.

For reasons not completely understood, pests can be quiescent for many years and then suddenly burst out as an area-wide problem. The blue alfalfa aphid had not been a problem for many years, and even where numbers exceeded management thresholds, the pest was only sporadic.

The 2013 outbreak reminded growers and PCAs to look closely at the insects they find in their sweep nets and be prepared to see the unexpected. The blue alfalfa aphid may be found during the same time in late winter and early spring as the more common pea aphid, and it will be important not to confuse the two pests. If the blue alfalfa aphid is found, treatment thresholds will be much lower than if only the pea aphid is present.

Statewide IPM Program, Agriculture and Natural Resources, University of California
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