Researchers seek solutions as diseases grow tolerant to fungicide

01/15/2014 05:00:00 AM
Tom Burfield

Edward Sikora, Auburn University; bugwood.orgTo control labe blight in tomatoes, use a protective fungicide, monitor your field, pay attention to late-blight alerts and use a late-blight-specific fungicide as needed.Some years are worse than others when it comes to late blight in Florida tomato crops, says Pamela Roberts, professor of plant pathology at the University of Florida’s Southwest Florida Research and Education Center in Immokalee.

Symptoms of late blight include brown lesions surrounded by a “white sporangial mass” that show up early in the morning on the leaves of the tomato plants, she says.

The condition also can cause “big brown, greasy lesions” on the fruit.

“If there is no control, or if the weather is conducive, it can destroy your entire planting within weeks or days,” she says.

Sometimes, regular fungicides, conventional farming methods and early detection are enough to control late blight, but other years, growers must take more aggressive action.

Often the fungicide mefenoxam, developed in the 1980s and marketed under the brand Ridpmil Gold as well as several other names, is effective in controlling late blight. But there’s no guarantee.

“You need to know your population every year as to whether it’s sensitive to Mefenoxam,” Roberts says.

If the late blight pathogen does show resistance to mefenoxam, some newer alternatives are available to which the fungi have not yet demonstrated resistance, she says.

Presidio, with the active ingredient fluopicolide, is one. Revus, with the active ingredient mandipropamid, is another. And there are even more on the market.

“Use a late-blight specific compound when there has been a specific outbreak and you want to protect your field,” Roberts advises.

The website tells highlights the latest outbreaks.

“Late blight usually is manageable,” she says, if you use a protective fungicide, monitor your field, pay attention to late-blight alerts and use a late-blight specific fungicide as needed.


No longer a rarity

Tomato late blight used to be a fairly rare occurrence at Lipman, an Immokalee-based tomato grower, says Gerry Odell, chief farming officer. But he says in recent years, it’s been turning up pretty much every season.

“The university will tell us when late blight first shows up,” he says.

The university also will alert him about whether the strain is sensitive to products that contain mefenoxan, Odell says. Then he’ll decide which to apply.

“We try to use as many different chemistries as we can that have activity against late blight,” he says.

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