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Aphid Populations Being Observed in Wheat

During the past couple of weeks, reports of aphid populations in wheat fields have slowly been increasing. Typically, the initial aphid populations are observed earlier in the season, but the 2019 spring may have delayed infestations. So far, the populations have been relatively small but there is the potential for them to grow rapidly as conditions become more favorable. The most commonly observed aphids currently are the English grain aphid, but there is the possibility for other species to be observed. The other two species of aphids are the bird cherry oat aphid and greenbug.

Aphid Identification

Two, dark green aphids on a bright green leaf.
Figure 1. Bird cherry oat aphids.

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 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

To scout wheat for aphid populations the easiest way is to start at one side of the field and walk in a “W” of “Z” pattern. While walking either pattern, randomly choose twenty plants from each leg and examine for aphids. During the spring, 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 thresholds, please refer to the most current edition of the South Dakota Pest management Guide: Wheat. As mentioned, the cool, wet conditions that were experienced during the start of this year likely slowed the development of aphid populations down. But warmer weather will encourage more rapid populations growth.

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

Barley Yellow Dwarf Virus

Picture of a wheat field with yellowing leaves throughout.
Figure 4. Wheat plants with Barley yellow dwarf symptoms. Plants with BYDV have purplish yellow leaves.

The three aphid species can transmit Barley yellow dwarf virus (BYDV) (Figure 4). However, aphids being found in winter wheat at this time are not responsible for BYDV symptoms being observed at this time. These symptoms are from fall infections. BYDV infections that take place at this time may not have impact on yield since winter wheat plants are further along.

Related Topics

Wheat Insects, Wheat Diseases