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Russian wheat aphids found in ColoradoColorado Dryland wheat and barley producers should be aware of the presence of Russian wheat aphids in the state. Mike Koch, northeastern Colorado entomologist, wrote the following at late April 23: "A scouting trip throughout Washington County today revealed Russian wheat aphid presence in all wheat fields. The area covered was Highway 59 on the east, Highway 36 on the south, Highway 71 on west, and Highway 34 on the north. There are fields with 25 percent symptomatic tillers with RWA on the edges. Tillers do not have large colonies of aphids. Most had between one and 10 aphids, even when severe symptoms were present. As we know, populations can increase rapidly." Scouting your wheat fields for the presence of Russian wheat aphid (RWA) is the best way to avoid a costly pest outbreak or to needlessly treat for pests that become newsworthy but are not at economic levels in some to many fields. Fields and parts of fields often have different infestation levels of RWA. Therefore, fields with relatively low RWA infestations may be adjacent to one or more fields having aphid populations above the economic treatment threshold level. Field pest scouting is an important aspect of maintaining farm profitability and sustainability. Russian wheat aphid can affect other small grains, especially barley, but will not affect corn, alfalfa, sugar beets or other field or rangeland crops. I have looked at wheat in fields in Morgan and Logan counties and have found signs of this pest as well but, in all cases, they were below the economic treatment threshold level. Russian wheat aphids were not found in all fields but I was not focused on pest scouting. A simple economic treatment threshold for this pest is when 5 to 10 percent of the tillers have damage symptoms and aphids present. A more complete, and complex formula for determining the economic threshold is based on the price of wheat, cost of treatment, and a field's estimated yield potential. It can be found at the High Plains IPM website, www.highplainsipm.org under crops and small grain pests. It is important to check plants from 10 to 20 locations of wheat or barley fields to determine the infestation levels. Randomly collect 100 tillers from different locations across each 80-acre field or portion of a larger field. Avoid scouting at field margins where many pests concentrate.
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