2014 Hays Wheat Field Days

(Jim) Good morning I’m Jim Shroyer, Extension Wheat Specialist at Kansas State University. (Erick) And I’m Erick DeWolf, Extension Plant Pathologist for Kansas State University. (Jim) Well, we’re here at Hays, the experiment field at the Wheat Field Day. And in other parts of the state and here as well, we normally think of leaf rust and stripe rust being problematic over the whole state. But because of the drought this year, we’re not seeing much leaf rust or stripe rust or wheat streak mosaic. And that’s where I’m heading is toward wheat streak mosaic. You know, it’s a western Kansas disease but we’ve seen a lot of it in south central, even southeast over the last couple of years. So tell us a little bit about wheat streak and what we have here behind us. (Erick) OK, so wheat streak is certainly one of the top three diseases in western Kansas right after stripe rust, leaf rust and then the wheat streak mosaic. And as Jim has pointed out, it is being reported at a higher frequency in central Kansas and even as far east as near Kansas City. So, that’s some areas where it’s historically been quite rare and the varieties of course are playing a big role in that as well. So, in the central and eastern part of the state we’ve seen some increase in acreage of some varieties that have a little higher degree of susceptibility as well. (Jim) Right. (Erick) So, varieties like Everest are known to be quite susceptible to it. But we do also have some varieties that have a high level of genetic resistance. And we’re kind of excited to have some of those tools that are available and as we do a lot of these variety demonstration talks, we are trying to highlight some of those varieties. And some of you may be wondering where some of those ratings come from. And it’s demonstration plots like we have behind you that in this case we deliberately expose to the virus and have a direct comparison between the virus exposed, virus infected plants and healthy plants that allow us to make a head to head comparison. (Jim) So you’ve got them side by side. (Erick) That’s right, they’re side by side type of comparison of virus infected and uninfected and some 40 different varieties that may be options for Kansas growers. (Jim) I know we’re in western Kansas, but what are some of the possible reasons why wheat streak is moving more into more central or we are seeing it more and more. We always think about volunteer wheat being that green bridge between harvest and the next crop that’s coming on, but is there something else going here? (Erick) Well, I think there’s maybe a couple of different factors that have to play with some of the increased incidents. One, is it’s been hotter and drier in central Kansas, so in some ways you can say the climate that often prevails in western Kansas that is so conducive historically to the wheat chromite and the wheat streak mosaic virus has in many ways been occurring at more higher frequency in central Kansas as well. So, the other factor would be in those failing corn because of again the drought stress or sunflowers. Maybe people have maybe neglected some volunteer wheat out of just necessity or other problems with these row crops that would otherwise be rotated within central Kansas. (Jim) But you can also have coming out of a pasture and maybe a yellow foxtail and maybe even corn is… we’re seeing more corn in the central part of the state, so could there be something with that as well? (Erick) Absolutely. Historically we’ve emphasized volunteer wheat a lot but there are other places that the virus can survive and the chromites can survive including corn. It also has a history of coming out of some grassy weeds particularly around grassy ditches and waterways around fields.

(Jim) So Erick, we’ve got a brand new variety here. So what is the
difference between these two rows? (Erick) This is part of the wheat streak demonstration plots here at Hays. And the outside rows of this Oakley CL plot were not exposed to the virus and the inside rows were exposed to the virus. So, the Oakley CL is known to have a resistance gene called wheat streak mosaic two and that particular gene confers a high level of genetic resistance to the virus and I think that’s what we’re seeing here. If it was more susceptible we’d expect to see stunt gene and potentially some yellow discoloration, often a more prostrate growth habit of the wheat that’s infected with the virus. So the fact that we’re not seeing that is a really great thing. It’s an indication that the virus is being held in check by the resistance gene and all things are looking good. (Jim) So, there’s not much difference between the two rows here of the same variety, treated and untreated. What’s the little nuance that we treat mosaic wheat gene number two? What’s the nuance about losing it’s tolerance? (Erick) So what Jim is talking about there, is there is a weakness to this WSM2 gene in that’s temperature sensitive. So once we get to temperatures up into the mid 80s, even 90 degrees that resistance gene is no longer highly effective. So, it’s primarily an issue if we plant wheat in the last summer months, say for a grazing purpose when the temperatures are quite warm. And we shouldn’t expect a high level of control then out of that genetic resistance. So if we plant normal, close to normal times, by the time the wheats up and growing well, we shouldn’t run into too bad of a problem losing its tolerance. But as soon as the temperature drops back down, it’s still… it kicks back in, right? (Erick) Well, there’s some evidence coming out of Texas suggests that maybe it doesn’t kick back in so effectively but I think what Jim is also highlighting there, is if you do have that virus in populations suppressed or the resistance of the virus held in check by the resistance gene well into the fall, the early stages of growth when the temperatures are cool, that even if you do get some hot weeks or a few hot days in the spring of the year the resistance should be effective long enough that the virus wouldn’t have enough time to cause a lot of damage. (Jim) Well, let’s stop right here and let’s go back to one or two varieties that are highly susceptible and take a look at the difference so kind of get a visual idea of the height here of the two lines, strips here and let’s go back in the back here and take a look at another variety. (Erick) Sounds good.

(Jim) So Erick here we are in front of WestBred’s variety Cedar, which is a great variety. It’s a shorter variety to begin with, early maturing, great yielding variety but wow, look at the difference here in the expression of the disease. (Erick) That’s right. So you know, Cedar one of the things we’ve known about it in the past is or concerns we have about it is, it’s susceptibility to wheat streak mosaic and it sure shows up in these inoculated demos. Remember the inside row was exposed to the virus, the outside row was not. So this is kind of what we would expect Cedar to look like in this environment. But here where it’s infected with the virus you have a lot of stunting, more prostrate kind of sprawled out growth pattern, and a lot of yellow discoloration of the leaves as well. (Jim) More of that typical mottling that we see by a virus. (Erick) That’s right. What we often will call a mosaic type of symptom on the plants. So, usually intensifying as you reach the upper third, two-thirds of the leaf and transitioning to a little darker green at the base. But again, it’s the stunting reduced green leaf area that really causes profound yield loss that we experience. (Jim) And shows how much later it looks like to be, because it has a disease. It’s stunted and not only in stature but in delayed maturity as well. (Erick) I think so, and I think one of my concerns there would be of course that it would get caught in hot, dry weather towards the end of the season. So even though it may produce some grain, those kernels… the plants are not only damaged by the virus and could be shriveled because of that but also that delay in maturity sets it up for a lot harsher environment as it reaches those key stages of kernel development. (Jim) Big difference among the varieties here. So Erick thanks for sharing this with us. (Erick) Thank you Jim.

 

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