When it comes to aphids in wheat there are a couple of species that producers may have concerns with during the growing season. The well-known greenbug (Schizaphis graminum) and Russian wheat aphid (Diuraphis noxia) are both capable of reaching damaging levels in wheat fields. A few other aphid species may also be present that play a more insidious role in the field; the English grain aphid (Sitobion avenae) and bird cherry-oat aphid (Rhopalosiphum padi) may ring a bell. Both of these species are important mainly due to their role as vectors of plant viruses, especially Barley Yellow Dwarf Virus. A third species, and one noticeably present in canola and wheat fields this season in southwest Kansas, is the green peach aphid (Myzus persicae). Like the English grain and bird cherry-oat, the green peach aphid could be a concern mainly due to its ability to transmit viruses; over 100 viruses have been found to be transmitted by this species! The green peach aphid has hundreds of potential host plants and it is during the summer that the aphids feed widely on a variety of plants; their primary overwintering hosts are trees of the genus Prunus (peaches, plums, etc.). Not only can one find these aphids in wheat and canola this season, but even in the home garden and on ornamental plants purchased at local nurseries, these aphids get around!
“The green peach aphid adult with nymphs. Also visible, a mummy, the handiwork of a parasitoid wasp.”
Thresholds for this aphid can vary depending on the time of year and growth stage of the plant infested. In Canola, a Fall threshold would be 100-200/plant while a Spring threshold is 50-80/plant. In wheat, it may be prudent to treat the green peach aphid like its other virus-bearing friend the bird cherry-oat aphid. Treatment for control of the green peach aphid in wheat may be considered when there is an average of 50 or more aphids per tiller from boot stage to heading. But remember, treatment with contact insecticide will not reduce the transmission of viruses on already infested plants. The good news is that the green peach aphid is typically held below damaging levels by the suite of beneficial insects already hard at work on other aphid species. Additionally, the presence of a few species of mostly benign aphids in a field can help bolster the populations of the beneficial insects that are vital to keeping more serious crop pests in check.
The green peach aphid may be recognized as a mostly nondescript green to yellow aphid lacking the characteristic single dark green stripe of the greenbug. However, some individuals may display a characteristic set of three darker green stripes along the top of the abdomen. The aphids’ cornicles are elongate with darker tips while the tarsi and antennae from the midpoint to tip are also typically darkened.