Fungicides provide major boost to crop yields

Spore Wars: That's the movie take-off term Leonard Gianessi uses in discussing the very important role that fungicides play in U.S. and world crop production.

From strawberries to peanuts to pecans and a host of other crops in between, major increases in production have paralleled the development and adoption of effective fungicides, he says.

Gianessi, who heads the Crop Protection Research Institute, a non-advocacy research organization that focuses on the economic analysis of agricultural pests, pest management, and pesticide use/regulation, says U.S. producers — including organic growers — apply more than 100 million pounds of fungicides every year to battle fungi that could otherwise wreak havoc with crops.

“Thousands of different organisms release spores into the environment,” he said in outlining results of a CPRI study to members of the Southern Crop Production Association at their annual meeting at Orlando, Fla. “One tiny mushroom can release as many as 30 million spores. The prolific production of spores in the environment represents an immense potential threat to crops. Most acres of fruits and vegetables have fungi present and growers must deal with the problem each year.”

The study, which looked at 50 crops and 231 diseases that are controlled by fungicides, spanned the entire lower 48 states. Some of the findings:

83 percent of U.S. onions are sprayed with fungicides; in Georgia and Texas, growers can make as many as 10-11 applications. But the treatments result in a 30 percent production increase — 1.3 billion pounds of onions that could otherwise be lost to disease.

Scab, a perennial problem in southern pecan orchards, was treated for half a century with copper and lime. But when effective synthetic fungicides became available in the 1960s, yields that had been averaging only 8 pounds per tree jumped to 20-25 pounds per tree. Estimates are that without fungicides pecan growers would lose 53 million pounds yearly and $46 million in income.

Peanut producers suffered major losses from Rhizoctonia, “a truly awful disease,” and leaf spots until the advent of effective fungicides, which have resulted in yield increases as high as 2,000 pounds per acre. “Ninety-nine percent of the acreage in the South is infected with late leaf spot and 80 percent by early leaf spot,” Gianessi says. “Without treatment, plants are defoliated and you've got just brown sticks.”

Watermelon growers in the South were losing as much as 90 percent of their crop to bacterial fruit blotch, a disease that appeared in 1989 and spread throughout the region, turning melons to “a nasty bacterial mush.” With fungicides, losses now are minimal.

U.S. apple producers were suffering 25 percent to 50 percent losses from black rot and peach growers were losing as much as 75 percent of their crops to brown rot. Modern fungicides have cut those losses to 1 percent to 2 percent. In Georgia alone, peach growers got added production worth $35 million, a return of $17-$18 for every $1 spent on fungicides.

“Through the 1940s, U.S. apple producers were harvesting an average of 50 pounds per tree,” Gianessi says. “They were spraying lime, sulfur, and arsenic to control fungi, but heavy doses caused heavy damage to the trees. When the first effective fungicide became available, apple yields doubled, then tripled. The new materials were kinder and gentler to the trees, didn't damage bark, roots, and leaves, and the trees responded with greater production.

“A single cucumber infected with Phytopthora can release 80 million spores during the season. It's a pernicious disease, because you can't see it until it's too late. With fungicides, growers can produce healthy, beautiful cucumbers.”

The first widespread use of fungicides occurred in France in 1854, after powdery mildew had wiped out 75 percent of the winegrape production. “Sulfur was used to kill 100 percent of the fungus, and it has been used now for 150 years. It is the No. 1 fungicide, by volume, used in the U.S. — and an extremely valuable tool in vineyards worldwide.”

And though little mention is made of it, Gianessi says, fungicides are widely used by organic growers.

“It's very common for organic fruits and vegetables to be sprayed with fungicides. A Rutgers University study of organic apple production in the Northeast found that it's common to spray 10 gallons of lime/sulfur per acre and 12 pounds of wettable sulfur. Apple growers simply can't tolerate scab, whether they're conventional farmers or organic farmers.

“The University of California says a typical acre of organic winegrapes in that state gets 66 pounds of sulfur per acre — but do you ever see pictures of organic vineyards being sprayed? No, they don't talk about it, and the press never reports it.”

Conventional potato growers may make 9 to 15 fungicide treatments in a season, Gianessi says, “but organic growers may use even more, because the copper they use doesn't have as long a residual effect as the synthetic fungicides.

There was a big scandal in the United Kingdom when the British Broadcasting System reported that organic potato growers were treating their crops with copper fungicides.

“Consumers assume sprays aren't used on organic farms, and the media have gone along with it. But the fact that these materials are being used by organic growers just emphasizes how important fungicide use is to crop production.”

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