According to Mary Burrows, Montana State University Extension Plant Pathology Specialist, problems with wheat streak mosaic virus have been showing up on wheat from Montana’s golden triangle. Below is a Montana Ag Alert she issued Tuesday discussing the problem. For the full list of alerts, visit MSU’s website.
Cropland disease. Wheat streak mosaic virus symptoms in the triangle (1 May, 2011)
I’m pretty surprised due to the dry fall we had, but I’ve gotten several samples of wheat streak mosaic virus (WSMV) this spring. Some seem to have been due to fall infection (widespread, no mites); others do have active wheat curl mites down in the crown and/or young leaves on the plant. Here are a couple of things you should know:
- Spring wheat is highly susceptible to WSMV. To eliminate the green bridge you need to spray out your crop and wait 2-3 weeks before planting. Yes, 2-3 weeks before planting. You need the green plant material to die before the seedlings emerge, otherwise the virus and mite just infest the new crop.
- WSMV is facilitated by the green bridge. There are no chemicals that will either cure plants or stop the spread of the wheat curl mites. There are no chemicals for mite control. Most insecticides require contacting the insect – mites hide in leaf whorls and crowns, so efficacy is limited.
The most important things to be thinking about now are how to treat the winter wheat crop.
- Do not add additional nitrogen to the crop – the virus and mite would LOVE that. Our data shows greater yield losses at higher nitrogen levels, and higher mite reproduction when there is sufficient nitrogen versus a nitrogen-stressed plant.
- Eliminate the green bridge this fall. If it’s common in your area, your best bet is to get all the neighbors together and everyone needs to do a good job of cleaning up the fields of all volunteer and grassy weeds before planting. I know this is tough, especially given the sawfly situation. Given favorable conditions mites can travel 3 miles.
- Plant winter crops late and spring crops early to avoid mite activity.
Some things you might want to know:
- Symptom severity does not necessarily correlate with yield loss. That is, even if it looks really bad it still might not lose that much yield. For example, the variety Yellowstone, although it always looks bad, only looses ~15{fd15d42d1b024b97d6d50958be27cc8145b6addb99e015780abccf2984117bb0} of its yield with an early, severe infection.
- Yield loss is going to depend on the weather and variety – so don’t ask me to predict how much yield you’re going to lose. I’m going to say anywhere from 10 to 100{fd15d42d1b024b97d6d50958be27cc8145b6addb99e015780abccf2984117bb0}. Yes, it is frustrating.
- Legumes (peas, lentils, chickpeas), mustards and any dicot crop are not susceptible to WSMV.
- We’ve found a high association of WSMV with cheatgrass. So, volunteer wheat and cheatgrass are big risk factors. So is late maturing spring wheat and early planted winter wheat. Mites love it somewhat cool and moist.
- A hot dry summer would be good for getting rid of the mites – they can’t fly long distances when it’s hot and dry, and they don’t reproduce as well.
- A hot dry summer will be bad for WSMV-infected plants. They don’t root as deeply and will be more drought stressed.
If you submit a sample to the clinic, please dig up a number of plants, put the soil in a plastic bag and tie it apart from the leaves with a twist tie or something – otherwise, when it’s shipped the soil gets all over the leaves and damages the sample. Pack it loosely in a box, not an envelope, with newspaper or something – do not get the foliage wet. Send it overnight, and not on Friday. We can use a laboratory test on these samples but it takes some time.
More information about Wheat streak mosaic virus can be found on the High Plains IPM website at http://wiki.bugwood.org/HPIPM:Wheat_Streak_Mosaic
A Montguide on cereal viruses can be found at http://msuextension.org/publications/AgandNaturalResources/MT200911AG.pdf
Some typical leaf symptoms:
Source: Montana State University
Posted by Haylie Shipp
