Darren Cockrell: Darren.Cockrell@colostate.edu
Dr. Punya Nachappa: Punya.Nachappa@colostate.edu
Wheat Stem Sawfly – Adult Emergence
Wheat stem sawfly larvae collected from Weld County were found to be in early stages of pupation with wing nodes present (Figure 1). Generally adult sawfly emerge 7-10 days after this stage, but this can be delayed by cool, wet weather. Adult sawfly can be found by using a sweep net along the field edge (Figure 2). Please let us know if you find any sawflies in your fields as we track the timing of the adult emergence. For wheat stem sawfly lifecycle information: https://extension.colostate.edu/topic-areas/insects/wheat-stem-sawfly-a-new-pest-of-colorado-wheat-5-612/.
Left: Figure 1: Wheat stem sawfly pupae from Weld County. Arrows indicate with wing nodes. Photo from Darren Cockrell. Right: Figure 2: Adult female wheat stem sawfly on wheat stem. Photo from Kelsey Dawson.
Russian Wheat Aphids
Russian wheat aphids (RWA) have been reported across the state in varying population densities, with many sites below economic threshold. A number of fields have been treated for aphid populations, especially in the southern part of the state. Aphids collected from Walsh, CO were found to be RWA biotype 2. More information on RWA at: https://extension.colostate.edu/topic-areas/insects/aphids-in-small-grains-5-568/
Other Cereal Aphids and Barley yellow dwarf virus
Barley yellow dwarf virus (BYDV) symptoms were observed by Wilma Trujilo in Weld and Prowers Counties. We could not find any aphids in the wheat or CRP near the fields.
BYVD can be transmitted by 25 different species of aphids but, the most common vectors are English grain aphid, bird-cherry oat aphid, corn leaf aphid and greenbug. Interestingly, RWA does not transmit BYDV. Infestations may occur at irregular spots within the field or as a general infestation throughout the field. As they suck plant sap, the aphid injects toxic salivary secretions into the plant cells. The toxin kills the cells and results in a yellow or reddish stippling on the leaves. Fall infections are most damaging, but spring infections do occur. A wide range of losses due to the disease has been reported. Management strategies include late planting, genetic resistance or tolerance, and control of weedy grasses as the virus can host on a variety of cultivated and wild grasses. Using insecticide treated seed should protect seedlings from fall infection and increased losses. Consider an insecticide application if aphid abundance exceeds the threshold levels. Glance ‘n Go and the Greenbug Calculator also can be used to determine the need to treat with an insecticide. (https://www.noble.org/news/publications/ag-news-and-views/2007/november/glance-n-go-a-simple-scouting-method-for-greenbugs/)
Brown Wheat Mites
Varying populations of brown wheat mites have been reported statewide, with some fields reaching high densities. Recent rain events will aid in reducing populations of brown wheat mites, however precipitation has not been uniform throughout the state. Even with heavy precipitation, high density populations of BWM have been found at ARDEC in Larimer County last week (Figure 3). Products containing Dimethoate are most effective at controlling the pest, however products containing chlorpyrifos should be considered if RWA are also present. For more information see: https://wiki.bugwood.org/HPIPM:Brown_Wheat_Mite_SG
Wheat Curl Mites
Wheat streak mosaic virus (WSMV) has been reported in Baca County, and is vectored by wheat curl mites. We also found wheat curl mites in wheat plots at ARDEC, Larimer County, but did not note any symptoms of the virus. For more information, please refer to Wheat Disease Update.
For wheat disease updates by Dr. Robyn Roberts, please see: https://coloradowheat.org/2021/05/colorado-wheat-disease-newsletter/
We would like to acknowledge the tireless work of the CSU researchers and extension agents for reporting pest problems throughout the state, including Ron Meyer, Todd Ballard, Jerry Johnson, Sally Jones-Diamond, Dennis Kaan, Wilma Trujilo, Kevin Larson, Brett Pettinger, and Laura Newhard, as well Dr. Frank Peairs for continuing to provide insight on pest problems during his retirement.