Scout Your Wheat for Russian Wheat Aphids

 By Jeff Bradshaw

Extension Entomology Specialist, Panhandle Research & Extension Center

The Russian wheat aphid, Diuraphis noxia, is a pest of wheat worldwide; however, the last time that Nebraska saw a serious outbreak of this pest was probably in the late 1980s following its introduction into the U.S. in 1986.

However, last June there were some fields in Kimball County that had reported heavy infestations of Russian wheat aphid in their fields and some required treatment.

Additionally, we noticed spotty presence of these aphids in our wheat at the Panhandle Research and Extension Center (PHREC) in late April 2021 as well.

This year we have again noticed some scattered symptoms in our wheat plots at PHREC yet again.

While I am not aware of any major infestations this year, I feel it prudent to make you aware of this pest if you are a wheat grower in the region. Furthermore, given all of the challenges that seem to be arising in wheat thus far this year that are outside of our control, I’d like to present at least one potential issue that you can manage – Russian wheat aphid.

Russian Wheat Aphids Do Not Transmit Plant Viruses

We often generally refer to aphids collectively in wheat as “cereal aphids”. For aphids such as English grain aphid, bird cherry-oat aphid, and corn leaf aphid virus transmission is generally the biggest concern.

Winter wheat can be at high risk to viruses (such as barley yellow dwarf) when aphids move to wheat after planting in the fall. This risk can be especially high for early-planted fields. That is, early-planted winter wheat can receive aphids from over-summering hosts that may also harbor wheat viruses. Viruses can be transmitted in the spring; however, it is thought that older plants have greater tolerance to virus infection.

Russian Wheat Aphids Can Cause Direct Damage to Wheat

A couple cereal aphids, such as Russian wheat aphids and greenbug, more commonly cause direct damage by their sap sucking activities alone and their numbers can build up rapidly to cause significant economic damage to wheat. For example, Russian wheat aphid can live for 60-80 days and produce up to 80 offspring when the ambient temperature is 68°F. Furthermore, an individual Russian wheat aphid is reproductively mature in about 8 days. That should give you a sense of just how rapidly a Russian wheat aphid population can grow!

Impact on yield from these aphids range about 0.5% for every 1% of infested tillers from tillering through flowering. Additionally, these yield impacts may be exacerbated by dry conditions.

Symptoms of infected tillers are very conspicuous (Figure 2). As the aphid colony develops and the aphids feed, leaf edges will roll and enclose the aphid colony in a protected, tubular leaf.

Once a colony is enveloped within this protective structure, natural enemies and insecticides can not reach it.

Additionally, infestations that develop on and roll flag leaves can trap the awns of the emerging wheat head, resulting in poor pollination. These curled heads can look very similar to 2, 4-D injury.

The Situation in Nebraska

In western Nebraska, we started finding Russian wheat aphids in April again this year. Aphid numbers at present do not appear to be high enough in western Nebraska to warrant treatment. However, cooler temperatures do extend the longevity of these aphids so conditions may be adequate populations to slowly build and then break out once the temperatures warm. Keep a close eye on your wheat fields now and into June for the development of aphid populations!

Scouting for Russian Wheat Aphids

Spring thresholds for Russian wheat aphids have been found to vary based on plant stage, but generally range from 5-20% infested tillers. However, for fields in which a marginal yield is expected (below 40 bushels/acre), you might consider a higher threshold as a larger amount of damage would be needed to justify treatment costs.

To sample, select 20 sample areas of a field at random and closely inspect five tillers at each of these sites for aphids. Use a total of at least 100 tillers per field (5 tillers per sample area) to estimate the infestation within a field.

Controlling Russian Wheat Aphids

Consideration of the natural enemy population is important as improper timing or use of some chemicals can reduce natural enemy numbers disproportionately to the pest and set back biological control activity. I won’t go into details here; however, there are several parasitoids and predators that will attack and keep aphid populations regulated in our wheat fields.

They offer the most cost-effective management action, so careful consideration of the above threshold is warranted.

Because these aphid populations tend to establish on field edges first, if detected early enough, border applications of insecticide in wheat can be sufficient to reduce Russian wheat aphids to a level that is below economic importance. Such treatment strategies may provide conservation of biological control and suppression of an aphid outbreak while saving on input costs.

For more information of thresholds and treatments options, see https://cropwatch.unl.edu/2022/scout-your-wheat-russian-wheat-aphids