Popular fungicides failing, may cause hard choices for apple growers

July 12, 2011

Orchard growers have started finding that some of the most commonly used fungicides are no longer effective at controlling apple scab, according to a Purdue University study.

Janna Beckerman, an associate professor of and , said that extensive, long-term use of four popular fungicides has led to resistances in apples in Indiana and Michigan, the focus of her study.

"The fungicides that are regularly used to control scab have started to fail," said Beckerman, whose findings were published in the early online version of the journal Plant Disease. "But the most disturbing thing we found is that many of the samples we tested were resistant to all four fungicides. It's kind of like multidrug resistance in antibiotics. This is full-blown resistance."

Apple scab, caused by the fungus Venturia inaequalis, is highly destructive to apples, causing brown on leaves and fruit. A single lesion can reduce an apple's value by 85 percent. Over time, the scabby lesion will crack and allow insects, other and bacteria inside, causing a loss of the crop.

"It can cause failures," Beckerman said. "An orchard grower that has this could lose blocks of an orchard, or depending on the amount of diversity in the orchard, they could lose the entire crop."

It's thought that when organisms adapt to form resistance, that change will weaken the organism in some other way. Beckerman said the study, done with Purdue graduate student Kim Chapman and Michigan State University professor George Sundin, showed apple scab, on the contrary, is becoming resistant to fungicides with no apparent fitness penalty to itself.

"Having these multiple resistances to fungicides doesn't debilitate them in any way," Beckerman said.

Apple scab samples were treated with dodine, kresoxim-methyl, myclobutanil or thiophanate-methyl. About 12 percent of the apple scab samples tested was resistant to all four fungicides.

The only options have, Beckerman said, is to use older that are tightly regulated, require more frequent application and are more expensive.

"It's going to change how growers manage their orchards," Beckerman said. "The more susceptible apple cultivars, like McIntosh, will become more chemically intensive to manage. Growers have few options as it is, and this will limit their options even further."

Beckerman said she and her collaborators would work to develop faster tests to detect fungicide resistance in to help growers change management plans in a timely manner. The U.S. Department of Agriculture, Purdue University and the Michigan Agricultural Experiment Station funded the research.

Explore further: WineCrisp -- new apple was more than 20 years in the making

Related Stories

WineCrisp -- new apple was more than 20 years in the making

January 22, 2009

A new, late-ripening apple named WineCrisp™ which carries the Vf gene for scab resistance was developed over the past 20 plus years through classical breeding techniques, not genetic engineering. License to propagate trees ...

Tough New Spuds Take on Double Trouble

March 3, 2010

(PhysOrg.com) -- Americans love potatoes, consuming about 130 pounds per person annually. But it's a wonder the spuds even make it to the dinner table, given the many fungal diseases that attack the tuber crop -- powdery ...

April showers bring May glowers from N.Y. growers

May 4, 2011

The first of May in upstate New York usually finds fields plowed, corn planted and apple trees sprouting leaves. But this year's record April rainfall -- 7.31 inches in Ithaca, more than double the 3.29-inch 30-year average, ...

Recommended for you

Researchers design first artificial ribosome

July 29, 2015

Researchers at the University of Illinois at Chicago and Northwestern University have engineered a tethered ribosome that works nearly as well as the authentic cellular component, or organelle, that produces all the proteins ...

Studies reveal details of error correction in cell division

July 29, 2015

Cell biologists led by Thomas Maresca at the University of Massachusetts Amherst, with collaborators elsewhere, report an advance in understanding the workings of an error correction mechanism that helps cells detect and ...

Researchers discover new type of mycovirus

July 29, 2015

Researchers, led by Dr Robert Coutts, Leverhulme Research Fellow from the School of Life and Medical Sciences at the University of Hertfordshire, and Dr Ioly Kotta-Loizou, Research Associate at Imperial College, have discovered ...

Stressed out plants send animal-like signals

July 29, 2015

University of Adelaide research has shown for the first time that, despite not having a nervous system, plants use signals normally associated with animals when they encounter stress.

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.