Darren Cockrell: Darren.Cockrell@colostate.edu,
Dr. Punya Nachappa: Punya.Nachappa@colostate.edu
Russian Wheat Aphids
Heavy infestations of Russian wheat aphids continue in southern part of the state and according to Kevin Larson at the Plainsman Research Center, many fields have been treated or are being treated for the pest. Drought in the southern parts of the state has been exacerbating the problem, however recent rain events may lower population growth of aphids and reduce their impact. Aphids collected from Walsh have been determined to be biotype 2, meaning that wheat varieties with Dn4 resistance will not be effective at deterring the aphids. Some Russian wheat aphids have been found in Larimer county as well. More information on Russian wheat aphid can be found at https://extension.colostate.edu/topic-areas/insects/aphids-in-small-grains-5-568/.
Brown Wheat Mites
Hot and dry conditions had worsened earlier reported brown wheat mite infestations in the Walsh, CO area, however recent rain events may help reduce populations. The economic threshold for this pest is not well defined, but during an outbreak spraying with insecticide is the only option. Previous research has shown that dimethoate insecticides are the most effective of currently registered products. Products containing chlorpyrifos should be considered if Russian wheat aphids are also present (see https://wiki.bugwood.org/HPIPM:Brown_Wheat_Mite_SG).
With warmer spring temperatures, army cutworms are very active or are beginning to pupate into adults. Some light cutworm damage has been reported in Washington County by extension agent Dr. Wilma Trujillo. More information on caterpillars in small grains can be found at: https://extension.colostate.edu/topic-areas/insects/caterpillars-in-small-grains-5-577/. Pyrethroid insecticides are effective against both army cutworm and pale western cutworm (https://wiki.bugwood.org/HPIPM:Small_Grains_Army_Cutworm).
Wheat curl mites and viruses
There are reports of wheat curl mites and wheat streak mosaic virus (and the wheat mosaic virus complex) particularly in wheat fields next to volunteer wheat in the Walsh, CO area. The virus cannot be managed once infection occurs and there are no effective miticides. Preventive practices such as destroying volunteer wheat and other grassy weeds are the best management strategy, and planting resistant varieties also may reduce losses.
Wheat Stem Sawfly Flight
Adult wheat stem sawfly emergence is expected to begin in approximately 1-2 weeks in the southern part of Colorado, and in 2+ weeks in the northern counties as the wheat is tillering. Typical adult flights last approximately 4-6 weeks. There is no effective way to control adult populations of wheat stem sawfly. There is no information on the impact of rainfall on wheat stem sawfly emergence.
For wheat disease updates by Dr. Robyn Roberts, please see: https://coloradowheat.org/category/news-events/wheat-pest-and-disease-update/
We would like to acknowledge the tireless work of the CSU researchers and extension agents for reporting pest problems throughout the state, including Kevin Larson, Brett Pettinger, Ron Meyer, and Wilma Trujillo, as well Dr. Frank Peairs for continuing to provide insight on pest problems during his retirement.