Rosy apple aphids leave apple trees in the summer to live on plantain, studies by Dr. Elizabeth Beers and colleagues at Washington State University show.
Reporting to the Washington Tree Fruit Research Commission, which funded the research, Beers said the literature indicated that the rosy apple aphid migrated to weeds during the summer, but that had not been observed in the field.
Her studies show that both broad- and narrow-leaf plantain are summer hosts of rosy apple aphids and that the insect does move back and forth between the weeds and fruit trees.
The scientists looked for aphids on weeds at 37 orchard sites in Washington and Oregon. Samples of plantain and other common weeds (dandelion, dock, lady’s thumb, lamb’s quarter, common mallow, white clover, and yarrow) were taken from in and around orchards every two weeks between June and October. No aphids were found on the other weeds, with the exception of two individual aphids found on white clover that were thought to be transient.
The winged adult, which migrates from host to host, is a brownish green or black. Aphid nymphs are rosy brown or purple with a powdery white coating.
“Part of the reason we’ve never seen rosy apple aphid on the summer host plant before is it looks nothing like the rosy apple aphid on apple,” Beers said. “On the summer host, it’s pale yellow and you see none of the salivary toxin symptoms, such as curling leaves or honeydew that you see on apples. They don’t look the same.”
In a greenhouse experiment, winged rosy apple aphids moved from potted fruit trees to plantain in early June and returned to apple trees in September. Although it appears that rosy apple aphid could survive exclusively on apple trees, Beers said the populations tended to die out when the weather got hot.