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Aphid Infestations In Spokane, Whitman Counties

Jul 24, 2014

By Dave Crowder, Entomologist, and Diana Roberts, WSU Extension Regional Agronomist

Peggy Greb - USDA ARS

Peggy Greb – USDA ARS


We have received reports of aphid populations increasing in small grain fields in Spokane and Whitman counties, with many growers treating for these pests. Several species of aphids occur in Washington wheat crops including the Russian wheat aphid, the bird-cherry oat aphid, and the English grain aphid. See the PNW Insect Management Handbook for pictures and chemical recommendations at PNW Handbook – Small Grain Aphid and PNW Handbook – Small Grain Russian Wheat Aphid. The cereal aphid is a relatively new species found in small grains, with more information available here.

Aphids can damage small grains crops through direct injury, by sucking plant nutrients directly from plant tissue, and indirectly by transmitting diseases such as barley yellow dwarf virus.

Aphids have historically been sporadic pests in small grains crops of Washington, and unfortunately reliable economic thresholds are not available. The small grains team will work to address this gap in future years. The general recommendations are that no treatments are recommended for most aphid species after the soft dough stage. Prior to this stage, recommendations for different aphid species vary:

(1) Russian wheat aphid –

The recommendation is to spray an insecticide if more than 20 percent of tillers are infested, because of the aphid’s ability to distort the head. This species can be identified by its pale green coloration. Its feeding causes characteristic white streaks on leaves, and leaf curl can resemble an upright soda straw. See more information at the link above.

(2) Bird-cherry oat aphid –

Data from California suggest that a density of 20 aphids per tiller will lead to an estimated 5 percent yield loss, while a density of 40 aphids per tiller will lead to an estimated 9 percent yield loss. Heavy populations may cause a golden yellow streaking on the leaves; do not confuse this with the white streaks caused by Russian wheat aphid. However, this species can also transmit barley-yellow dwarf virus, particularly to young plants, so the economic threshold is 1 to 2 per head at the flag leaf stage. However, these thresholds are rarely reached.

(3) Cereal aphid –

This is a new invasive pest to Washington State. Researchers at the University of Idaho have begun to investigate this pest and more information into their work can be found here. Currently no economic thresholds exist.

Aphid predators include parasitoid wasps, lady beetles, lacewings, and damsel bugs. Populations of these beneficial species are typically highly effective for controlling aphids in Washington small grain crops. Populations of predators can increase rapidly and species such as ladybeetles and parasitoids can kill hundreds of aphids per day. If you do choose to spray for aphids, softer pesticides with reduced impacts on these predators, such as neonicotinoids, are likely to be more effective. In contrast, organophosphates typically have greater negative impacts on natural enemies. See the links in the first paragraph for specific pesticide options for each pest, and be sure to follow label instructions when treating for aphids.

Source : wsu.edu