FORT COLLINS, Colo. — Wheat curl mite (WCM) transmitted viruses including, Wheat streak mosaic virus (WSMV), Triticum mosaic virus (TriMV) and High Plains wheat mosaic virus (HPWMoV) continue to cause yield losses in the Great Plains (Fig. 1A). Plants infected with WSMV show yellow to light green streaks that coalesce to form a mosaic pattern (Fig. 1B). Symptoms are more severe if plants are infected early in their development and can include stunting, poor fertility/sterility, and reduced grain set. Average yield losses range from 2-3%, but localized affected areas can have much more dramatic losses of up to 100%.
Tessa Albrecht, a research associate in Dr. Punya Nachappa’s lab determined virus presence in wheat samples that were collected from the field by researchers or submitted by extension specialists and wheat producers for diagnosis in 2019 and 2020. We found high rates of virus incidence in symptomatic wheat samples (Fig. 2). In 2019, 95% of symptomatic field samples tested positive for one or more WCM-transmitted viruses, whereas, in 2020, 75% of samples were positive with relatively low symptom severity. Last winter brought colder than average temperatures to Colorado that may have reduced the number of mites that were able to overwinter into 2020. Furthermore, the WCM cannot survive in high temperatures and dry conditions, which maybe another reason for limited spread of the virus in 2020.
Our research revealed new WSMV isolates collected from Colorado. Fourteen out of the 22 WSMV isolates analyzed were collected from cultivars carrying either virus-resistance (Wsm2) and/or mite-resistance (CmcTam112) genes. Moreover, a couple of isolates were 100% similar to a potentially resistance-breaking isolate reported from Kansas. We plan to screen Colorado’s elite germplasm with these new variants to determine potential for resistance breakdown as part of our recently funded Colorado Wheat Research Foundation grant.
The WCM is a challenging pest to control owing to their short development time, high population growth rate, thermal tolerance and wide host range. Planting mite and virus-resistant varieties has been effective in reducing disease spread. However, there have been reports of mites adapting to resistance genes and emergence of novel, potentially resistance-breaking WSMV isolates. Hence, controlling this disease complex requires a multi-faceted approach which includes elimination of oversummering alternate hosts such as volunteer wheat, corn and wild grassy weeds, which prevents mites moving back to wheat as it begins to emerge. Delayed planting can also reduce fall infections by minimizing the overlap between wheat and alternate hosts. Research has shown that planting prior to September 15th puts wheat at a higher risk for curl mite infestation and viral infections in the fall. Another way to delay resistance breakdown is planting varieties with both mite and virus resistance such Colorado State University-developed ‘Guardian’, which will ensure improved and more durable resistance than mite or virus resistance alone.
–Tessa Albrecht and Punya Nachappa
Department of Agricultural Biology, Colorado State University
For more articles out of Colorado, click here.
RECOMMENDED ARTICLES
MANHATTAN, Kan. — The optimal planting dates for next year’s wheat crop are now open across much of Kansas, but agronomists are cautioning producers to carefully watch and mitigate pest and disease issues as planting season gets underway. “Choosing the right date to plant is harder than circling a date on the calendar, but Kansas […]
MANHATTAN, Kan. — Early sowing of wheat can lead to several problems, from increased chances of insect- or mite-transmitted viral diseases to decreased emergence due to high temperatures and its consequences on wheat germination of particular varieties and reduced coleoptile length. Ideally, growers should consider planting around the optimum window; but, if planting early due […]
MINNEAPOLIS — The hot, dry growing season has led to infestations of two-spotted spider mites in many areas of Minnesota. Over the past two weeks, increasing numbers of fields with economic infestations have been observed. Most, but not all, have been in areas with obvious drought stress. Soybeans appear to have the heavier infestations although […]
FORT COLLINS, Colo. — Stripe rust was found at low incidence and low disease severity in several northeastern counties (Figure 1). The past two weeks of cool, wet weather has been favorable for disease development. The extended hot weather forecasted over the next week should help control disease development since stripe rust spores germinate poorly […]
FORT COLLINS, Colo. — Tan spot (caused by the fungus Pyrenophora tritici-repentis) was observed in Prowers, Kiowa, Cheyenne, Kit Carson, Washington, Yuma, and Phillips counties. Tan spot appears as necrotic (dead, brown) diamond-shaped spots surrounded by yellow halos or borders (Figure 1). Tan spot was found only on the lower leaves (not advancing to the […]
