Wheat Curl Mite & Viruses In Wheat

 

In North Dakota, wheat curl mites are being found in spring wheat and winter wheat knodel.1samples. Wheat curl mites vector wheat streak mosaic virus (WSMV) and the High Plains virus (HPV). Symptoms of WSMV include yellow longitudinal stripes in the leaves, and yellowing.

 

 

 

The NDSU Plant Diagnostic Laboratory (Source: J. Ostrander) confirmed the presence of WSMV in winter wheat (91% of samples submitted), spring wheat (6% of samples submitted), and durum wheat (3% of samples submitted) in the following counties (number of samples in parentheses):

 

The High Plains virus also has been confirmed in Dunn (3 samples), Hettinger (1 sample), McHenry (2 samples) and McLean (1 sample) Counties (Source: J. Ostrander, NDSU Plant Diagnostic Laboratory).

 

Dr. Mary Burrows, Extension Plant Pathologist at Montana State University, said that “An outbreak of wheat streak mosaic virus could lead to 100 percent crop losses in some northern Montana counties in 2016. To keep the disease from continuing into next year’s crops, Burrows is working with growers and county agriculture agents in the affected areas to till fields this year and then delay planting in the fall to keep infected mites from moving into the new crop.” See MT YouTube video

 

Wheat curl mites are white and carrot-shaped, but are microscopic (1/100th of inch) and not visible to the naked eye. These mites overwinter in all life stages, and have a short life cycle of only 8-10 days at 77 F. Hosts include wheat, corn, foxtail, millet and grassy weeds. Wheat curl mites feed deep in the curled leaves or whorls and are protected from pesticides. Injury from leaf feeding is minimal and secondary to the deadly vectored viruses.

 

During heading, mites move up to the heads and can affect yields by 10% under very high mite populations. Winds readily disperse mites from an infested field to neighboring fields.

 

 

I’ve received many questions about how to control wheat curl mites with insecticides in wheat. Unfortunately, we have NO insecticides registered in wheat that will reduce wheat curl mite populations. Neonicotinoid insecticides such as imidacloprid (Gaucho) and thiamethoxam (Cruiser) are systemic insecticide seed treatments commonly used for control of soil insects (such as, wireworms), but are NOT effective against wheat curl mites. In fact, field studies have shown that imadacloprid can increase wheat curl mite populations. Wheat curl mites hide deep in the curls of wheat leaves and are inaccessible to insecticides. The bottom line is that there are no currently labeled insecticides with proven efficacy against wheat curl mite. Please avoid ineffective and costly pesticide applications for wheat curl mite.

 

The best control strategy is breaking the ‘green bridge’ by destroying living plant host material with tillage or herbicides for at least a two week period prior to planting winter wheat. Mites must have GREEN living host plant material to survive, and can only live for 48 hours off of a host. Herbicides that kill the mite’s hosts quickly will lower the chances of mite survival; otherwise, slow-acting herbicides allow mite to disperse off the dying plant host for more than 7 days. Tillage will kill mites faster than herbicides, especially in dry conditions. Cool temperatures (40-50 F) will slow down mite reproduction whereas warmer temperatures (70-80 F) will speed up mite reproduction and increase the likelihood of dispersion to other fields.

 

The long warm fall of 2015 favored mite development and virus transmission, so any winter wheat that was planted in early to mid- September would be at the highest risk for infection. Early planting in fall does not break the ‘green bridge’ and allows for a longer period for mites to develop and transmit viruses. It is best to avoid early planting of winter wheat in the fall.