Ominous news: Destructive wheat streak mosaic arrives early
Deep down in your heart, you knew it was going to happen.
With all the volunteer wheat we had this past summer and fall, what are the odds that the new wheat crop would not get infected with wheat streak mosaic virus?
Correct. The answer is zero.
As we all know, wheat streak mosaic is a very serious viral disease. It is transmitted to the new wheat crop by microscopic wheat curl mites that have been living on volunteer wheat, which serves as the intermediate host. At some point in their lives, these tiny little mites make their way to the edge of the volunteer wheat leaves, and then they just jump off. The wind carries them very long distances until they land on another wheat plant. Then they go to work.
A plant pathologist explained to me once that the mites have snouts just like hogs and they root around on the wheat leaves, rupturing plant cells. They feed on that plant material, and at the same time, they’re infecting the plant with the wheat streak mosaic virus, which they carry in their little bodies.
This virus can be extremely dangerous. I have personally seen wheat yield reductions of near 100 percent in areas of fields adjacent to heavily infected volunteer. Usually, though, you won’t see the actual damage until later next spring. If you are seeing symptoms in the fall, you have a real problem.
Well, we have a real problem. I was talking recently with Lane County Extension Agent Chris Long, who told me that a farmer east of Dighton had him out to look at a wheat field that he suspected was infected. The farmer said it wasn’t planted all that early, but there were fields of big volunteer on two sides of the field at planting time. Chris took some plant samples and sent them to K-State. And, yes, it was wheat streak mosaic.
Chris said this is the first time in his career that he’s been asked to look at fields and to get samples in the fall to see if the problem is wheat streak mosaic. “I’ve been asked on a number of occasions to get samples in the spring, but never in the fall.”
This is really bad news for several reasons. Chris looked at the field recently and said, “The field on Monday looked pretty much entirely destroyed by the disease. But in addition, the wheat variety was Oakley CL, which is supposed to have extremely good resistance to the disease. On a scale of 1 to 10, Oakley had been rated a 2, and the next best resistance to it are several varieties with ratings of 5.”
In addition, a Scott County farmer said that several wheat fields that had been planted quite early for wheat grazing had also been killed. However, I am not sure what those varieties were.
Kansas State University wheat breeder Allan Fritz said there are two potential issues with Oakley: “One is that the resistance is temperature-sensitive and even if the field weren’t planted early, the warm conditions could have caused the resistance to not be effective. There is also the possibility the virus has changed and now overcomes that resistance gene.”
Fritz went on to say that they have screened some new wild relatives for wheat streak resistance. “There are some promising candidates, but it’s too early to tell what we will be able to get out of it.”
Fellow wheat breeder Guorong Zhang confirmed that they have found a new race of wheat streak mosaic virus at Hays which can break the resistance gene in Oakley.
Making our situation even more precarious is the fact that we’ve had a very long and mild fall. Here in Lane County, we didn’t have a hard-killing frost until the first week in November – almost three weeks late. That has given the wheat curl mites even more time to do more damage.
And if you think seed treatments are going to help minimize the problem, think again. I asked K-State plant pathologist Erick DeWolf and K-State entomologist Sarah Zukoff about whether seed treatments with insecticides would help with control of wheat streak mosaic through control of wheat curl mites.
DeWolf said, “I am not aware of any seed treatments that would influence wheat curl mite populations and, thus, reduce risk of WSM.” Zukoff added, “I haven’t seen any data that says seed treatments will work on fall armyworms, army cutworms or wheat curl mites.”
Pulling things together, there is still a fair amount of volunteer wheat out there that has not been controlled. I know it is late in the day, but you can do yourself and the entire neighborhood a favor if you get that stuff killed. And finally, if you are going to plant early for grazing, forget wheat and go with rye or triticale. Both will produce a lot more forage than wheat will and you won’t have to worry about wheat streak mosaic.
Vance and Louise Ehmke grow certified seed wheat in Lane County.