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4 Points To Consider About Corn Fungicides

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Thinking about applying a fungicide to your corn this year? How about two? What kind should I apply? Here are some points you should consider when it comes to corn fungicides this summer. 

1. Data is split on the merits of early corn fungicide applications. 

Early corn fungicide applications often occur between between V4 (4 leaves with visible leaf collars) and V7 (7 leaves with visible leaf collars) growth stages. Typically, these are teamed with a postemergence herbicide application. This lessens application costs, compared to a tasseltime corn fungicide application. 

Randy Myers, Bayer CropScience product development manager, notes Bayer research shows an average 7 bushel per acre increase in corn from an early Stratego YLD fungicide. If you’re already applying a postemergence herbicide at that time, the product cost of the Stratego YLD is another $8 per acre, he says. 

“Even with $3 (per bushel) corn, you can make an extra $21 per acre for a cost of $8 per acre,” he says. (This is just product cost, as the application cost applies to the postemergence herbicide you would normally be applying).

Besides an additional $13 per acre profit in this case, Myers says early fungicide applications can aid stalk health. “We see benefits later at harvest,” he says. 

Early and later season fungicide applications don’t replace each other, though, says Myers. Early-season applications can reduce the amount of fungal inoculum moving up the plant.  However, it doesn’t protect against fungal disease like southern rust that blows in later in the season. Fungicide applications made closer to tasseling helps control these diseases, says Myers. 

University research suggests more mixed results. University of Missouri trials in 2011 and 2012 showed that although disease severity may be reduced, V5 herbicide and fungicide co-applications in corn are not likely to increase corn grain yields compared to just herbicide treatments alone. Three fungicides were tested in these trials. 

If you only have money for one fungicide application, stick with tasseling, say university plant pathologists. A compilation of 13 university and on-farm trial studies compiled by Carl Bradley, University of Illinois Extension plant pathologist, showed an average 1.3 yield increase for fungicide applied at the V6 stage, compared to a 7.9 bushel per acre increase for VT applications. 

2. You still might have to spray twice. 

Normally, Northern Corn Leaf Blight (NCLB) occurs later in the summer, under moderate temperatures 64 and 81 degrees F and wet and humid weather. Last year, though, cool 2014 summer weather prompted NCLB to arrive six weeks earlier than normal. In some cases, farmers who sprayed at tasseltime had to spray again at R5 to treat for NCLB. “Fourteen to 21 days later, if disease pressure remains high and if conditions are conducive to disease, another spray treatment can be beneficial,” says Myers. “Even at R5, disease can impact corn yields.” 

3. Disease-resistant hybrids don’t resist all diseases. 

Hybrids can have resistance to some diseases and not others. For example, some hybrids may resist Gray leaf spot (GLS), but not northern corn leaf blight (NCLB). 

“You may say you have a hybrid that resists gray leaf spot, but not northern corn leaf blight,” says Myers. “It is important to get into fields and know what is going on.” 

4. Apply two fungicide modes of action.

Patent protection for several fungicides will soon be expiring. That means generic products will be coming on the market. 

One advantage is generic prices will be lower. If you use them, though, make sure they have at least two different fungicide modes of action. 

“Stay away from straight strobilurin fungicides,” Myers advises. “It is critical we need to preserve the value of these tools by using two modes of action is important. Other fungicide action modes for corn and soybeans include triazole and SDHI fungicides. 

One drawback is although SDHI fungicides give another action mode, their disease control spectrum is limited. Thus, it’s important to still keep disease control in mind, he adds. 

 “We have to be smart about how to manage disease resistance going forward,” says Myers. 

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