To spray or not to spray

Garrett Lindell of Lindell Aerial Ag Service in Aledo, Ill., was always taught you need three factors for a disease to spread: a host, the right environment and a pathogen. With its humidity and temperatures, he has all three in west-central Illinois, a perfect growing house for gray leaf spot, one of corn’s worst opponents.

“It seems like the disease can explode over a week’s time with the right environment,” Lindell says. “At times, I’ve talked farmers into not spraying, then we do test strips, and I wish I would have kept my mouth shut.”

In the Northeast, as well, and down the coast, moisture off the ocean provides the right environment for gray leaf spot on corn, a blight caused by the fungus Cercospora zeae-maydis. Essentially, it’s a mildew-like sunblock that prevents the leaves from absorbing the benefits of the sun. Like with any fungus cool, wet weather makes the disease worse.

Early lesions on corn leaves are yellow to tan in color, with a faint watery halo visible against a light source. After about two weeks, the lesions appear tan to brown and rectangular, bordered by the veins of the leaf. When fully expanded, individual lesions may be 3 to 4 inches long and 1/16 to 1/8-inch wide, according to Patrick E. Lipps and Dennis R. Mills on The Ohio State University Web site.

If several infections occur on the same leaf, a broader lesion will result. The light brown color continues until environmental conditions are right for conidia (spores) to form, at which time the lesions take on a silvery-gray cast, though hybrid colors exist, and some hybrids’ lesions may also be on the leaf sheath and stalk.

This loss of leaf area results in less sugar production, then less grain. Extreme leaf damage leads to premature plant death and diminished production and value of the corn as silage.

Gray leaf spot on corn.
Department of Plant Pathology Archive, North Carolina State University, Bugwood.org.

When did gray leaf spot arrive?

It has been known in the United States since 1924, and was first reported in Illinois. Until the 1970s, gray leaf spot was a minor pathogen with only occasional outbreaks. With the increased use of reduced and no-tillage practices, gray leaf spot has augmented, particularly in the more humid corn-growing regions. The worst infestations are mostly from low-lying areas and river bottoms, where there are longer periods of leaf wetness and high relative humidity.

If the fungus overwinters in and on left corn debris, by late spring conidia develop on residues in response to warmer temperatures and increased humidity. Windblown, the spores attach to the present season’s plants, and infection can occur by mid to late June. The disease spreads rapidly by late July and August.

How widespread the disease and how effective treatments are on it depends on variables, many of them geographical. “It doesn’t seem to affect every part of the country the same,” says Matt Crabbe, a crop duster with successful operations in Mechanicsville, Va., and Elizabeth City, N.C. “It depends on humidity and planting technique, and whether a farmer is planting corn on corn [and not rotating crops or allowing a field to lie dormant a season].”

Crabbe lives near five rivers where fog often sets in and presents a breeding ground for gray leaf spot. He often sprays three farms within a 25-mile radius on the same day.

Controlling gray leaf spot

Hybrids are available with moderate resistance to gray leaf spot. Crop rotation and clean plowing are also effective. A two-year crop rotation away from corn is effective if reduced tillage is maintained for conservation purposes, or a one-year rotation with clean plowing in fields with histories of the blight, according to Lipps and Mills. Weed control will help increase airflow and dry the canopy faster, reducing the wet environmental conditions.

There are also fungicides, and there’s been an increased demand for spraying in the past four years, not just on corn, but also soybeans and wheat, too, which has produced better yields and overall plant health.

Lindell says his spraying operations on corn and other crops have witnessed incredible increases. In 2006, he sprayed 50,000 acres with corn fungicide, then in 2007, 350,000 acres, and by last year, 400,000 acres.

“There’s certainly an issue with it,” says Lindell, who has been spraying for 20 seasons. “It’s a battle, but what has changed is the chemistry. Chemical companies have changed the specifications. What we were using in 1992-93, say, was a band-aid, a preventative, but not a curative.”

Syngenta’s Quilt, for example, is a preventative, and also a curative. Material costs $7 to $15 an acre, or $25 to $40 an acre applied. “It’s one application, but two modes of action,” Lindell says.

BASF has similar fungicides in Headline for corn and TwinLine for wheat. Headline was marketed along with a simultaneous spike in the price of grains in the winter of 2006.

“Corn prices went through the roof,” Lindell recalls. “I was … with a friend [who farms in Illinois], and he said I’d better get another airplane because the prices were jumping. Farmers began saying, ‘Well, if the crop is worth something, if I can get more bushels of it, I’m going to do it.’”

Satisfied customers and applicators

Dennis Ebie, a grower in Mogadore, Ohio, has used Quilt on 400 acres of corn to control northern leaf blight and gray leaf spot. His corn, he says, was definitely healthier. “It was a lot greener where we sprayed, and we are very pleased with the results and know that we’ll have a great yield from it,” he says.

Likewise, Danny Bender in Poseyville, Ind., applied Quilt on his farm’s white corn. “We believe in the two modes of action that Quilt offers,” he says. “Food-grade condition is very important and there was definitely a visible difference. The corn matured naturally, held its greenness and was much healthier.”

Crabbe, whose Crabbe Aviation LLC has relied on chemical improvements for 17 years, credits the chemical companies’ marketing plans. “The interest has been a boon to all in the agricultural industry, farmers, all of us,” he says. “Crop dusting is a business.”

It is also a science, when you’re trying to perfect your craft like Crabbe, who treats about 25,000 acres of corn a year. He’s been testing strips for four to five years. Spraying makes even the stalk healthier, and on the East Coast that’s important. “If there’s a bad hurricane that demolishes a corn field, and you have a healthier stalk, that could help,” he says.

Lindell says the disease affects 99 percent of the corn in his region. From mid-July through the start of August, he sprays commercial corn once (“the cost to growers is too much to treat it twice,” he says), and sprays sweet corn two or three times.

A perfect application is late in the season when the corn begins tassling and pollinating, Crabbe adds. Spraying enhances the ears and plant health, and keeps test weight up as the plant staves off drying until as many as two weeks later.

Affecting commodity prices

Typically, Lindell says there’s a 15 to 25-bushel difference in yield from treated corn. Crabbe once noted a 44-bushel spike. Lindell has witnessed a 60-bushel improvement, which makes a big difference at $3.80 a bushel if it’s now $6. At 10 bushels, that’s almost $40 more in return for a $26 to $27 an acre spraying package. “If I can put $13 more in profit (per acre) in my pocket in a five-month turnaround, that’s better than the stock market,” Lindell says.

Plus, the staying ability at harvest allows a farmer to harvest at 5 mph instead of 1 mph if the corn is down, so it reduces harvesttime and costs.

“The bottom line is that when the sun is shining late in the season, whether you hire us or buy your own rig, late-season fungicides dropped from an aircraft are going to save you money,” Crabbe says. “You’ll run machines a lot more in fields where the corn has been knocked down. Aerial application is less expensive.”

Lindell says the more progressive farmers are realizing and reaping the benefits, though the smaller growers still can’t justify it. “They’re saying, ‘I’m not going to spend any more money,’ even though it would be best if they spent it,” he says.

The author has been published in national and regional magazines as well as daily and weekly alternative city newspapers. A gentleman farmer in Quakertown, Pa., he writes about people, social trends, historic preservation and 18th century America, agrarian culture, land use and sports and recreation topics.