Considering yield limiting factors in the fungicide decision


first_imgShare Facebook Twitter Google + LinkedIn Pinterest There is no question that disease issues are plaguing Ohio crops this year due, in part, to the unbelievable stretch of wet weather in many parts of the state. With that in mind, many corn and soybean producers are considering fungicide applications.Even with diseases present, though,  there are several factors at work in fields to think about with the economics of this decision to protect the plants from yield loss. It costs between $30 and $40 per acre to apply fungicides in corn, which requires preventing around 10 bushels of yield loss to break even. With the extensive challenges facing crops this year in many areas, the yields may not be there to protect. If leaf diseases are not the most yield limiting factor in a field, fungicides will likely prove to be an unnecessary expense.AgriGold agronomist John Brien has been finding early stalk rot problems in corn fields that may eliminate any benefit from fungicide application. This early in the season, stalk rot could limit the vital nutrient and water uptake to produce strong yields and limit grain fill potential significantly. Because of this, part of the decision to add inputs to corn fields should be based on the stalk health and other yield limiting factors.“The corn roots, stalks and leaves are the critical factory parts. As we start going out in fields and breaking open stalks we are seeing some interesting things early in the growing season,” Brien said in mid July. “Normally when we split a stalk open this time of year we see very juicy green vascular tissue. The nodes are light colored and clear. That is the sign of a healthy stalk that allows nutrients and water to move back and forth. What we are seeing now is quite the opposite. We are seeing stalks that have a lot of white cottony pith to them and our nodes are turning brown. We typically see this at the end of the grain fill period. We are seeing this at the beginning of grain fill this year and I am concerned about if we will have enough nutrient and water flow up and down the corn plant to fill this ear. This is a good sign that we may be seeing a lot of stalk rot pathogens moving into corn plants. Stalk rots start as root rots and root rots are mainly started due to saturated fields.”In terms of soybeans, Ohio State University Extension research by Laura Lindsey and Anne Dorrance found that disease was not the yield-limiting factor in soybean fields with significant flooding, so flooded fields were unresponsive to fungicide treatments. A positive yield response to strobilurin fungicide applications at the R3 growth stage at six out of 16 locations (around 38% of the time) in 2013 and 2014 with a range of yield increase from three to 12 bushels per acre. The responsive sites averaged higher disease levels than unresponsive sites.“There are several factors that I have found in the past that can influence this return on investment: growth stage of the plant, conditions that are favorable for disease and the presence of inoculum,” Dorrance said in a recent CORN Newsletter. “The take home message is: only spray if the field has a history of Sclerotinia stem rot or lesions of frogeye leaf spot are already present, the variety is susceptible, and you can get the fungicide on at the appropriate growth stage.”For Sclerotinia, if a variety has a good level of resistance, then it is probably not going to give a very large return following fungicide applications at the same level that a highly susceptible variety might — which can be as much as 50% of the yield saved.“If the field has been too wet to spray, and it is now in full flower or past flower, it is too late,” Dorrance said. “The infections would have occurred and all of the fungicides labeled for Sclerotinia must be on the plant prior to inoculation or the spores landing on the plant.”Frogeye leaf spot has also been showing up in fields.“When I evaluate fungicides for efficacy towards frogeye, I use a variety that is super susceptible. On the company rating scales where 9 is the worst, we are right up there with a 7, 8 or a 9.  When this happens, lesions will start to be pretty easy to pick out around flowering. We then apply fungicides at the R3 and can save some yield,” she said. “When we wait until the R5 with just a few lesions here and there, we do not see any increase in yield and often there are still very few lesions on the new leaves.”If frogeye can be easily found in fields in 2015, Dorrance recommends one fungicide application at the R3/R4 growth stage.“We are also moving more towards a triazole type of chemistry due to good efficacy. Change up the mode-of-action this year in case we have strobilurin resistant strains, as well as reduced cost of material,” she said. “If it turns hot and dry, you may not need this. If we have cool nights, in the untreated strip checks (yes, please leave a couple in your fields), there should be the continued development of disease.”Moving forward, varietal resistance will be important after 2015.“Work with your company contact to know the true resistance level of the variety. If the variety has a few spots, but is believed to have good resistance, this will prevent too many more spots from developing as well as reduce the amount of Sclerotinia stem rot that develops,” Dorrance said. “The reason you purchased that top-notch variety is so you would not have to worry about the added costs to your production for the fungicides — so don’t spray in these situations. Your homework is paying off.”last_img

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