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Will a fungicide on wheat pay?By David G. Hallauer Meadowlark District Extension Agent, crops, soils, horticulture Let me say up front that I don't know. If I did have that predictive power--oh, the possibilities. That said, we can make a decision as to a fungicide application and whether it will pay by considering a few key factors: variety, yield potential, price of wheat, cost of treatment, and the risk of infection. Understand, some of these are: a) already set or b) very difficult to predict (see paragraph one.). So, let's boil it down a little finer based on a compilation of fungicide application results from 1991-2007 compiled by Extension wheat pathologist Dr. Erick DeWolf. During this time frame, 162 fungicide evaluations were done at various research sites across the state. The results are quite interesting. The average yield response: 9 percent (range of 4 to 13). When disease pressure is low, the response drops dramatically. If severity is below 10 percent on the flag leaf during grain fill, the response is only 4 percent. If disease severity is above 10 percent during grain fill, indicating a higher disease year, the average response is 10.5 percent. Put those figures into an equation with a $20/acre treatment cost and $8 wheat, and we see that you'd need about two and a half bushels to pay for the fungicide. With a 9 percent average response, wheat would have to have a yield potential of 27 to 28 bushels per acre to justify the fungicide. What does that mean? Scout this spring. Look for fungal diseases and determine their severity. Do so early--you'll be better off. Know your planted variety characteristics and focus on those with poor disease packages. If a fungicide is applied, do so in a timely manner. KSU research indicates that fungicides applied at jointing or before have not resulted in positive yield responses most of the time (usually less than one bushel/acre). Plan to scout early this year. Stopping iris leaf spot starts now If iris leaf spot has gotten you down, now is the time for some preventative work. Iris leaf spot can only be helped by two things, and one of those should be timed for right now. If plants were heavily infected last year, you need to start a spray program as soon as the leaves appear, with plans to spray four to six times at seven to 10-day intervals. Recommended treatments include chlorothalonil (Daconil) or myclobutanil (Immunox), he said. Add a spreader-sticker, too, to ensure good spray coverage to the waxy leaves. Once the disease is in check, the only additional control needed may be to remove and either discard or destroy the plants' old, dead leaves in late winter or early each spring before new growth starts. That will prevent the overwintering fungus from spreading. The infection appears as little reddish-rimmed spots, often surrounded by what looks like water-soaked leaf tissue. The spots turn yellow and expand. After bloom time, they can be large enough to join together. At times, the disease just kills individual leaves, though that can make for an ugly planting. The real problem is that every leaf spot attack also reduces plant vigor. So, if the disease is left unchecked, the irises may very well die when exposed to other stresses. 4/7/08 Date: 4/3/08 Advertisement
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