Low-Level Aphid Populations Present in Wheat

Written with contributions by Shelby Pritchard, former SDSU Extension Pest Management Specialist.

Originally Submitted: June 9, 2022

We are starting to receive reports of aphid populations in wheat fields throughout much of South Dakota. So far, these populations are well below the economic threshold, but there is a potential for them to increase. At this point in the season, weekly scouting is the best bet to monitor the populations.

Aphid Identification

Bird Cherry Oat Aphids

Two dark green aphids with rusty patches on a green plant
Figure 1. Bird cherry oat aphids. Courtesy: Adam Sisson, Iowa State University, Bugwood.org
 

Bird cherry oat aphids can vary in color from olive to dark green and can be identified by the characteristic burnt, red-orange patch that is present on the end of the abdomen near the cornicles or “tailpipes” (Figure 1).

English Grain Aphids

Many yellow-green aphids with dark antennae and cornicles on a stem
Figure 2. English grain aphid. Courtesy: Adam Varenhorst
 

English grain aphids can vary in color from light or dark green to brown and can be identified by characteristic black antennae, cornicles and leg joints (Figure 2).

Greenbugs

A small group of light green aphids on a green plant.
Figure 3. Greenbug. Courtesy: Alton N. Spark Jr., University of Georgia, Bugwood.org
 

Greenbugs are a species of aphid that are light green in color and can be identified by the dark green stripe present on their back. Feeding by this species causes yellow discoloration and red spots on the leaves, due to a toxin present in its saliva (Figure 3).

Scouting for Aphids in Wheat

The easiest way to scout for aphid populations in wheat is to start at one side of the field and walk in a “W” or zig-zag pattern. While walking the pattern, randomly choose twenty plants from each leg and examine for aphids. During the spring, the aphids are most observed on the leaves and stems of the plants. Table 1 contains the economic thresholds for the three aphid species that we observe on wheat in South Dakota.

If populations exceed the thresholds, please refer the most-current edition of the South Dakota Pest management Guide: Wheat. The forecasted temperatures for the next week will be favorable for aphid development in wheat. Also, it is important to remember that treating wheat when aphids are well below the threshold does not ensure season-long suppression. These prophylactic treatments may result in aphid increases over time, as insect predators are removed in addition to any aphids that are present.

Table 1. Economic thresholds for aphid pests of wheat.
Pest
Number of Aphids Per Plant
-
Seedling
Stage
Boot to Heading
Stage
Flowering
Stage
Milky Ripe
Stage
Milk to Medium
Dough Stage
Bird Cherry Oat Aphid
20
30
>5
10
>10
English Grain Aphid
30
50
5
10
>10
Greenbug
5-15
25
>25
>25
>25

Related Topics

Wheat Insects

Related Content

Green wheat leaves with yellow streaks throughout.

Wheat Streak Mosaic Virus Complex: Breaking the Green Bridge

As wheat harvest proceeds, it won’t be long until winter wheat planting is underway in South Dakota. To effectively reduce wheat streak mosaic virus, it is important to manage the green bridge effect to slow spread of disease in newly emerging wheat fields.

Wheat plants infected with wheat streak mosaic virus.

Volunteer Wheat and Kochia Management With Herbicides Will Likely Require Two Passes

Wheat curl mites, which carry wheat streak mosaic virus, use volunteer wheat and grass weeds as secondary hosts to infest recently planted winter wheat crops. Therefore, effective management of these plants before winter wheat planting is critical.

Multiple grasshoppers feeding on a corn ear.

Grasshopper Populations Continue to Cause Issues in South Dakota

Recent reports of crop loss along field edges indicate that grasshopper populations in some areas of South Dakota are well above threshold. Unfortunately, crops are often the target of these moving populations.