Stu Duncan Shares When it Pays to Spray Fungicides

(Dr. Stu Duncan): Hi, I’m Stu Duncan, Northeast Area Extension and Crops and Soils Specialist for Kansas State University based out of Manhattan, Kansas here at the Kansas River Valley Fall Field Day at the Rossville unit and tonight I visited, we visited about, “When does it pay to spray fungicides on your corn or your soybeans”. And there was a lot of background — the whole purpose of the fungicide is to stop a disease. There are certain fungicides that have a stay-green effect with them and so that is another drawing point or selling point on them. Over the time as we have looked at these though the results have been really mixed. You need to have a host that’s susceptible, you need to have a hybrid or as in cases of soybeans, a variety that is susceptible to the disease and in our case most of what we looked at was gray leaf spot in corn– there were soybeans very rare, we had very rarely infestations of soybeans diseases maybe a little frogeye leaf spot but not much. So we mostly concentrated on corn tonight. Gray leaf spot is a major disease in Kansas right now. We start scouting for that, well two to three weeks prior to tasseling and so a good scouting program is very critical to this. Planting a resistant hybrid is also critical. Also our farming practices have changed so much that we have a lot more residue left at the start of the next cropping season. We plant a lot more continuous corn and both of those will contribute to gray leaf spot in our following corn crop the next year because the disease can survive on the residue and then splash and blow up in the field if the weather conditions are right or the environment– high humidity, warm temperatures, moist conditions and when we are under irrigation we can keep it pretty moist most of the time. Our results have shown and very similar to what researchers in other states have shown is if we don’t have high level of disease, rarely will it pay us to spray our corn for gray leaf spot suppression. Off and on we’ve had good pretty good responses and actually usually when the price has been better we haven’t seen the magnitude of responses or the consistency that we see when our prices have been lower and as I think about that many times our prices are higher because our conditions and growing conditions are not as good. Where we’ve had some of our best responses over our breakeven cost and we just consider the, we figure the breakeven yields as the bushels per acre is going to fluctuate from year to year again depending on cost. When we’ve had our lowest prices we’ve actually– the 14, 19 or 2014 and 2015, we’ve had more yields go above the breakeven cost, percentage wise, with our fungicide treatments than when we had high yields or excuse me when we had high prices. So essentially under the best growing conditions that’s when we’ve seen our most consistent responses. Still not real high, not what I would like to see them but anywhere from 30 to 60% is about what we’ve seen for a consistent response above breakeven price. That includes the cost of fungicide and application essentially is what it is, that’s just another variable — input cost that goes into our corn budget. We’ve had a lot more issues getting a consistent response out of soybeans and the Southeast Kansas– many of the cooperatives down there and closer to the Missouri River they feel like they’re getting a good response because they are getting some insect control. We haven’t been able to achieve much of a response including insecticide and the spray treatment, maybe a little positive yield response but that additional seven to 10 dollars an acre that goes on with the insecticide in with the fungicide, we just hadn’t been able to recoup that on a consistent basis.

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