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Warm, wet weather leads to busy summers for fungicide applicators

By Matt Reese

Early July’s heat and humidity set the stage for diseases, the need for crop scouting and, maybe, a helicopter.

After he lost a potato crop to a spray application mix-up Stan Sayre decided to get into the aerial application business with a helicopter of his own. That was in 1976. Now, based in Portage County, Sayre travels Ohio offering a wide array of application services, covering around 70,000 acres per year per machine. He is busy this time of year with corn fungicide applications.

Helicopters have advantages when it comes to fungicide applications in corn.

“We can get into smaller fields a lot more economically than planes can. We can wrap up the corners. They have their speed of 140 or 150 knots and we are running 50 to 60 knots. We have a little better control with that. It is a 38-foot boom and we get almost 50 feet of coverage,” Sayre said. “We know our capabilities and we know what our machine is capable of doing. We can out work an airplane in areas along wood lines because we can go along the woods line a lot tighter than they can because they are running too fast. But in the big fields their operating costs are cheaper. We have to keep our costs down.”

Every minute running the helicopter costs about $20.

“Everything is a time item part on this and there are a lot of moving parts,” Sayre said. “They fix the next load while I am spraying. They have it ready so that when I hit the ground I am down basically a minute and a half to pick up 150 gallons and I get back in the air. We use high speed pumps to fill.”

With conditions right for disease development in Ohio’s crops in late June and early July, fungicide applications may be warranted this year in many fields.

Foliar diseases were beginning to show up in some corn fields in late June and early July.

“With warm, wet weather occurring across the eastern Corn Belt, now is a critical time to begin scouting for disease and determining whether or not fungicide applications are necessary. Over the last week our agronomy and sales staff and observed gray leaf spot (GLS) and northern corn leaf blight (NCLB) developing in our sales footprint,” said Matt Hutcheson, product manager for Seed Consultants, Inc., in early July. “The fungi that result in the formation of GLS and NCLB overwinter on corn residue. The development of these diseases depends on environmental factors. Warm, humid weather favors growth of GLS and NCLB. Periods of heavy due, fog, or light rain will provide the needed conditions for these leaf diseases to develop.”

Ohio State University Extension scouts reported heavier incidents of GLS earlier than normal, said Pierce Paul, Ohio State University Extension plant pathologist in a recent CORN Newsletter.

“This is not at all surprising, given that the crop was planted relatively late and it has been wet and humid in some areas. GLS is favored by humid conditions, particularly if temperatures are between 70 and 90 F. Foliar diseases of corn are generally a concern when they develop early and progress up the plant before grain fill is complete,” Paul said. “This is especially true when the hybrid is susceptible. In most years, GLS and NCLB usually develop late or remain restricted to the lower leaves. However, if it continues to rain and stays humid, this will likely not be the case this year.”

Due to wide variations in planting dates this spring, variable weather conditions, and hybrid maturities, the corn crop is at widely divergent growth stages. Scouting efforts should already be underway for the earliest-planted corn fields for foliar diseases, especially those planted with susceptible hybrids in an area with a history of foliar diseases or in continuous-corn, no-till fields, Paul said.

“Those are the fields most likely to benefit from a fungicide application. Use hybrid susceptibility, weather conditions, field history, and current disease level as guides when making a decision to apply a fungicide,” Paul said. “There are several very good fungicides to choose from. Follow the labels and keep your eyes on the fungicide price and application cost when making a decision.”

Paul said fungicide application decisions should also take the plant’s genetics into account.

  • Susceptible hybrids: If disease symptoms are present on the third leaf below the ear or higher on 50% of the plants examined, a fungicide is recommended.
  • Intermediate hybrids: If disease symptoms are present on the third leaf below the ear or higher on 50% of the plants examined, and the field is in an area with a history of foliar disease problems, the previous crop was corn, and there is 35% or more surface residue, and the weather is warm and humid through July and August, a fungicide is recommended.
  • Resistant hybrids: Fungicide applications generally are not recommended.

The timing of application has a tremendous impact on how effective fungicides can be, Paul said. Keep in mind, many fields are progressing very quickly this year with warm weather and ample moisture.

“Based on years of research, we have found that applications made at silking (R1) or tasseling (VT) are the most effective in terms of foliar disease control and yield response in Ohio,” he said. “Although we have seen a yield response to treatments applied between V4 and V10 in some years, the average yield increase is often low and highly variable when fungicides are applied before VT/R1. Similarly, on average, the yield response is much lower and more variable when fungicides are used under low disease pressure or in the absence of foliar diseases, than when disease is present.”

Another factor to consider with fungicides in corn is the potential for the crop. With great corn stands around Ohio, ample moisture headed into pollination and strong plant populations, AgriGold agronomist John Brien is more likely to pull the trigger on fungicide applications in corn.

“When I think about foliar fungicides as a broad acre application, disease is not the limiting factor. What I’m looking for is to preserve the yield we have. If you are in an environment where your stand is good, you have good moisture, your fertility is good and you have good potential, this is the year to think about putting on this fungicide,” Brien said. “The next logical step is a foliar fungicide application to control disease or protect your yield. The new fungicides on the market have a preventative and a curative. So if something is there, it is going to cure it and prevent future infection. When we think about preventative it is all about the corn plant’s response. As the corn plant tassels it is at the beginning of grain fill. We want to keep that factory as clean as we possibly can. By applying fungicide then we keep the plant healthy as long in the grain fill period as we possibly can. You get two or three weeks after that and you’ve missed a big window there for that protection.”

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