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Cereal Aphids and Soybean Aphids in ND (06/27/19)

The IPM Scouts have observed very low populations of both cereal aphids in wheat and soybean aphids in soybean in eastern ND.

The IPM Scouts have observed very low populations of both cereal aphids in wheat and soybean aphids in soybean in eastern ND. Cereal aphids were found on wheat near the NDSU Greenhouse complex in Fargo, Cass County on June 25th. Cereal aphids are also being reported on wheat in South Dakota and Minnesota. Soybean aphids also were found last week on soybeans in Walsh and Grand Forks Counties in NE ND. These are the first aphid detections for the season. See IPM scouting maps from last week on next page.

                Scouting is key to integrated pest management (IPM) and knowing when populations are getting close to the economic threshold level or action threshold. For a scouting protocol, walk a Z or W pattern across the field and inspect 10 randomly selected stems at 5 sites for aphids.

There are many natural factors that keep cereal aphids and soybean aphids in check. For example, strong thunderstorms can wash the aphids off leaves and drown them. Or, predators such as lady beetles, aphid lions, and syrphid larvae play a major role in reducing aphid populations. Parasitic wasps also help lower aphid populations. When natural enemies are present in large numbers, and the crop is well developed, farmers are discouraged from spraying fields.

Cereal aphids migrate into the northern Great Plains and do not overwinter in ND. Three primary species of aphids cause problems in ND wheat including the greenbug, the bird cherry oat aphid and the English grain aphid. All aphids are small, ⅛ inch long, and pear-shaped with two cornicles (tailpipes) on the posterior end. The English grain aphid is the most common aphid seen in small grains in ND and prefers the wheat head. The bird cherry oat aphid feeds primarily on leaves in the lower part of the small grain plant, and it is the most virulent aphid transmitting barley yellow dwarf virus (BYDV). When large numbers of aphids infected with BYDV are blown up from the south, BYDV can spread quickly through small grain fields. Symptoms of BYDV are yellowing of leaves, often the flag leaf, from the tip back toward stem, and stunted plants. BYDV has not been confirmed in ND yet this season. At greatest risk are later planted fields - much of our crop this year! Cereal crops are most susceptible to aphid feeding injury from the vegetative to boot stages. Scouting should begin as soon as cereal aphids are detected and continue up through the heading stage of wheat and barley.

Cereal Aphid Economic Threshold:  To protect small grains from yield loss due to aphid feeding, the treatment threshold is 85% stems with more than one aphid present, prior to complete heading. Heavy infestations of cereal aphids can reduce grain quality (protein and test weight), especially in early growth stages of cereal grains.

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Soybean aphids. This small aphid is yellowish-green, about 1/16 inch long, and pear-shaped with two black cornicles. They are commonly found feeding on the underside of the leaf and in the top ‘tender’ leaves of vegetative soybeans now. Aphids suck fluid from plants. When infestations are large, infested leaves are wilted or curled. The aphids excrete honeydew, a sweet substance that accumulates on surfaces of lower leaves and promotes the growth of black sooty mold. Start scouting fields in the V3 to V4 crop stage to determine if soybean aphids are present in fields.

Soybean Aphid Economic Threshold:

R1 (beginning of flowering) to R5 (beginning seed) = average of 250 aphids per plant and when populations are actively increasing in 80% of field.

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Janet J. Knodel

Extension Entomologist

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