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More on wheat fungicides for leaf diseasesBy Richard C. Snell Barton County Extension Agent, agriculture There is a fungus among us! Yes, leaf rust and powdery mildew are both in the vicinity of the Golden Belt. Last week, I warned you about the threat of leaf diseases to our wheat crop and the need to spray. I was anticipating. Well, after the 60 mile per hour wind gusts on May 2 and several days of rain, these conditions have caused rust spores that were down south to explode. If your wheat has 30 bushel yield potential, I feel you should be spraying with wheat at $8. Why do I say that? I will almost guarantee you that you will get a 10 percent return in yield. So, if you will gross $240, 10 percent would be $24 per acre. That is just about the cost to put fungicide on by air. As wet as it has been, aerial application may be your only avenue. Honestly, I think that the diseases are going to be bad enough that you will benefit more like 20 percent. That may not be true every year. It certainly would have been true last year. The problem is you usually have to make your decision about spraying before you know fully what the disease situation will be. So, everything is mostly hindsight. The actual costs of the chemical, depending on the product and rate you use, is between $11 to $17.50 per acre. You can hire a ground rig to apply it at say $3 to $5 per acre, which puts it in the range of $14 to $22.50 per acre total. If you apply it yourself, it is still likely to cost you $3 acre application costs. Not only is fuel expensive, but you have to figure your labor time, as well as the depreciation costs on your tractor and sprayer, as well as maintenance costs. What are the different fungicide products? We have many more choices and better choices than we used to after the soybean rust scare caused new product development a few years ago. First there are two preventative products - Headline from BASF and Quadris from Syngenta. They only prevent rust from developing. Then there are four curative fungicides. They actually stop leaf rust if it is less than 4 days active plus prevent new infections. These products are Bumper from MANA, PropiMax from Dow AgroScience, Tilt from Syngenta and Proline from Bayer CropScience. Bumper, PropiMax and Tilt are essentially the same compound with a different brand name. The third group of fungicides are combination products that are both curative and preventative and under some conditions may provide a greater level of protection. Remember though, a few years ago I got a 20 bushel response from using Tilt. These combination products are what most of our commercial applicators are using. There is Quilt from Syngenta which is a mixture of Tilt and Quadris. Then there is Stratego from Bayer. Quilt calls for 14 ounces per acre and Stratego calls for 10 ounces per acre. Normally, powdery mildew is only a problem when we have really cool springs. I mean "cool" in terms of temperature and spring in terms of the season of the year. It usually occurs with frequent showers or dewy mornings in a thick canopy of wheat. It won't likely be where the wheat is short and thin. It is more common on irrigated wheat, but last year it was prevalent in certain varieties even on dryland. Some of the more mildew susceptible varieties are 2145, Jagalene, OK Bullet, PostRock, NuHills and Trego. The wheat is behind normal in terms of maturity, so it could be affected more since the weather has remained cool and damp in our area. Some other leaf diseases besides rusts that can affect us severely are powdery mildew, speckled leaf blotch and tan spot. Usually these diseases are brought in by wet weather. Tan spot is encouraged by last year's wheat residue being present and these days we have a lot of no-till fields and wheat on wheat is not uncommon. I have not seen a lot of tan spot in recent years, but it could explode as well. You should be on the lookout, especially in no-till, continuous wheat. The two rusts that I mentioned, leaf and stripe, do not overwinter here but tend to blow up from Texas and Oklahoma on strong southerly winds which we frequently get in the spring. Wheats that are very susceptible to stripe rust are: Above, Bond CL, TAM 110, TAM 112, Trego, and last but not least, the poster child for stripe rust--2137. That alone tells you we didn't have stripe rust last year because 2137 and Sante Fe stood out as the two top varieties last year. It is hard to say if it will be a factor this year. This disease was nearly unheard of in the plains until about 10 years ago. The one we usually suffer the most from in terms of fungus disease is leaf rust. Leaf rust changes and adapts to a different race so quickly that even if a wheat is resistant when released, it is easy to have a variety go from almost totally resistant to highly susceptible only 2 to 3 years later. This is especially true if that variety is widely planted throughout Texas, Oklahoma and Kansas. Leaf rust likes warm weather, so it will get worse. Anything with Jagger parentage or the TAM wheats in general, I would see as candidates for spraying. Some of the most resistant wheats to leaf rust are: Fuller, Hawken, Millennium, Stanton, PostRock and Winterhawk. These are mostly newer varieties that the rust hasn't adapted to yet and you may not need to spray these. We have heard a lot lately about African rust and it's potential threat. This is a devastating disease that we do not have in the United States and hopefully never will. We have two good fact sheets at our office on fungicides and rusts. 5/19/08 Date: 5/15/08 Advertisement
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