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How to Push High Corn Yields Higher

Research says tasseling-stage applications of fungicides and fertilizer work best where environment already favors big corn yields.

Few researchers have studied in-season foliar applications of fungicides and fertilizers as intently as Kelly Nelson, a University of Missouri agronomist at the Greenley Research Center in Novelty, Missouri. 

Nelson recently answered four questions about foliar fungicides and fertilizers for corn.

1. When do foliar treatments pay off, and why?

Nelson: Our 54 site-year hybrid comparisons show that the probability of success for increasing yield from a foliar fungicide is greater in a high-yield environment (180 bushels per acre and up). Headline fungicide increased yields 6 to 9 bushels per acre compared with the control. The response was much smaller in low- and medium-yield environments.

Other factors such as weather, fertility status, and the ability of a hybrid to handle stress may be limiting factors in low-yield environments.  

Crop-production factors interact with each other. A high-yield environment may experience greater opportunities for disease, but yield increases are observed in the absence of disease also. 

2. When is the best time to apply a fungicide to corn to get an economic return?

Nelson: Our most consistent yield increases have occurred with a strobilurin fungicide, such as Headline, at VT (tasseling). We can’t predict at tasseling what the weather will do the rest of the season. However, the yield potential of the crop can be assessed, and the probability of an economical return is favorable if all other high-yield factors are there, such as nutrients, high-yielding hybrid, plant population, and other management factors.

Corn trial with fungicide

Corn trial without fungicide

Fungicides do the job in curbing disease in corn (top) vs. the result when they’re not applied (bottom) in University of Missouri trials. 

3. What are your results with foliar fertilizer applications?

Nelson: We’ve done research with Nitamin, a commercial saturated polymer solution with slowly available nitrogen (N) from urea, as a fungicide additive. 

A 1- to 3-gallon-per-acre rate of Nitamin did not impact yield in low- or medium-yield environments. If there is yellowing from a nitrogen shortage, we haven’t seen a yield increase with Nitamin. 

The amount of nitrogen supplied (a few pounds per acre) can’t overcome severe deficiencies. In these cases, a rescue application of N is recommended. 

In a high-yield environment, 1 gallon per acre of Nitamin increased yield 6 bushels per acre and, in some cases, up to 15 bushels per acre compared with no treatment. 

While significant, the economic benefit will depend on the relative crop prices and the cost of Nitamin in your location.

In contrast, grain yields were reduced 7 to 10 bushels per acre with Nitamin applied at 3 gallons per acre at our Novelty, Missouri, farm. This is probably due to increased plant injury at that higher level. 

4. Is there synergy in applying fungicide and fertilizer together?

Nelson: Our research indicates there is a promising synergistic benefit of Headline with 1 gallon per acre of Nitamin in high-yield environments.

Corn-on-corn’s Nitrogen sweet spot

Those of you who struggle with hardscrabble clay or rock-pocked soils would die for the deep, rich black soils oozing with 4% to 5% organic matter at the Beck’s Hybrids Practical Farm Research site near Colfax, Iowa. Corn planted in these soils can take advantage of generous nitrogen (N) applications.

Still, there’s a limit. Beck’s research found the optimal N rate for corn-on-corn is around 215 pounds per acre on this farm, says Wade Kent, a field agronomist for Beck’s Hybrids. 

Corn with N applications of 125 pounds per acre showed the telltale sign of leaf firing that signals N deficiency. But there isn’t an economic edge for rates as high as 250 pounds per acre, either, Kent says.

Corn-on-corn needs more N because there is typically a yield lag compared with corn following soybeans of 10% to 15%. Although there have been management strategies where the yield discrepancy narrows between 5% and 8%, corn-on-corn does need more N, says Kent. That’s particularly true as corn yields steadily increase each year at the clip of around 1½ to 2 bushels per year.

Soybeans, too 

Surprisingly, soybeans need N, too. Soybeans require 4 to 5 pounds of N per bushel of soybeans, says Chad Kalaher, a field agronomist for Beck’s Hybrids.

Soybeans manufacture much N via nodulation. Still, N applications have benefitted soybean return on investment (ROI).

Beck’s researchers added 30 pounds per acre of UAN on soybeans in a two-year trial. Stage and the per-acre ROI of the fertilizer application were as follows:

  • Preplant incorporated: $43.07
  • V6 (sixth trifoliate) sidedressing: $29.05
  • Broadcast application between R3 and R4 stages (podding): $24.15

On average, this tallied into about a $32-per-acre return from the N applications.

Opinion holds that adding N fertilizer will make soybeans lazy and not nodulate. Kalaher says that hasn’t surfaced in Beck’s Hybrids tests.

“Applying nitrogen to soybeans is one way to break through yield barriers,” he says.

More on Boron

Kelly Nelson has done several experiments with the micronutrient boron, and he says it shows promise in enhancing corn yields.

“Boron is important for reproductive functions in corn,” he says. “Ear-leaf tissue tests have indicated boron deficiency is common in the Midwest.”

His research has applied a combination of boron and fungicide in-season. While it increases tissue boron, it did not increase yields in this research. 

“A soil application of boron over 12 site-years of research on fine-textured soils testing low in boron indicates a 5-bushel-per-acre increase. I’d recommend soil testing and applying boron accordingly,” he says.  

Diagnosing boron deficiency at tasseling is too late to realize a yield benefit from a foliar application of boron, he says.

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