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Pea Aphid Populations Increasing in Alfalfa

While scouting alfalfa this week, we noticed pea aphid populations are starting to increase. The forecast is looking favorable for this pest, so it will be important to continue monitoring populations prior to and after the first cutting. Pea aphid population growth is highest when temperatures are around 70 °F, but they will slow down when temperatures exceed 90 °F. However, pea aphids tend to colonize alfalfa throughout the entire season. If pea aphid populations reach thresholds, they can be effectively managed using foliar insecticides. However, there have been some reports of pyrethroid failures when attempting to use this class of insecticides for managing pea aphid populations.

Pea Aphid Description

Teardrop shaped green insect with long legs and antennae on a lighter green leaf.
Figure 1. Pea aphid top view. Notice the dark tips on the “tail pipes”. Courtesy: Adam Varenhorst.

Pea aphid nymphs and adults vary in size, but adults are approximately 1/8 to 1/4 of an inch in length. Their larger size makes them more easily noticeable than other aphid species present on alfalfa. The nymphs and adults are generally light green-yellow or dark green in color. However, there is also the possibility to observe pea aphids that are a pale pink color. Pea aphids have long cornicles (tailpipes) on the end of their abdomen that are darker at the tips. Characteristics that are useful for identifying pea aphids include their red eyes and the dark bands present on their antennae (Figure 1).

For information regarding scouting and management, please refer our previous article on pea aphids.

Related Topics

Forage, Crop Management