Small Aphid Populations Observed in Wheat

Originally Submitted: May 13, 2021

This week we received the first report of aphids in wheat for the 2021 season. At this point in time, the populations are well below the economic thresholds (Table 1). The populations won’t be increasing rapidly until the daily temperatures warm up a little, but it is still a good idea to scout fields and determine if aphids are present.

Aphid Identification

Two, dark green aphids on a bright green leaf.
Figure 1. Bird cherry oat aphids. Courtesy: Adam Sisson, Iowa State University, Bugwood.org

Bird Cherry Oat Aphids

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).

 

Yellowish-green aphids on a yellow plant stem.
Figure 2. English grain aphid. Courtesy: Adam Varenhorst

English Grain Aphids

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

 

Bright green aphids on a dark green plant leaf.
Figure 3. Greenbug. Courtesy: Alton N. Spark Jr., University of Georgia, Bugwood.org

Greenbugs

Greenbugs are a species of aphids 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 Wheat for Aphids

The easiest way to scout for wheat aphid populations is to start at one side of the field and walk in a “W” or zig-zag pattern. While walking, randomly choose 20 plants from each leg of the pattern and examine them for aphids. During the spring, the aphids are most commonly observed on the leaves and stems of the plants. Table 1 contains the economic thresholds for the three aphid species. If populations exceed the thresholds, please refer to the most-current edition of the South Dakota Pest Management Guide - Wheat.

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

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