Optimism remains that valencias will do better against fruit drop

03/18/2013 11:38:00 AM
Tom Burfield

Fruit drop in Florida’s orange groves rose dramatically this winter, and growers have their fingers crossed that it’s not a harbinger of things to come.

Meanwhile, theories are flying about what caused this unusual occurrence.

According to a February report from U.S. Department of Agriculture’s National Agricultural Statistics Service, Florida’s all-orange forecast was 141 million 90-pound boxes—down 9 percent from the initial October estimate.

Early, midseason and navel varieties in Florida were forecast at 66 million boxes, down 9 percent from October and down 10 percent from the 2011-12 season.

“Projected droppage is the highest since the 1969-70 season, while size is projected to be below average,” according to the report.

Numerous theories

Theories abound for the unusual degree of fruit drop. But most agree that huanglongbing—also known as HLB or citrus greening disease—has something to do with it.

Bob Ebel, citrus physiologist at the University of Florida’s Southwest Florida Research and Education Center at Immokalee, attributes the surge in fruit drop to “a confluence of factors.”

First comes widespread citrus greening, he says.

Next, stress from last year’s drought may have predisposed fruit to drop early, Ebel says. But a cool spell followed by a warming pattern may have had an even bigger impact than the drought, he says.

Once the rain did come, it promoted growth.

“Essentially, what we’re seeing is an acceleration of the maturity of the fruit, which is really undesirable,” he says.

Sugar content and acid levels also were lower than what growers like.

Stressful situation

Bob Rouse, an associate professor at the Immokalee research facility, agrees that “a multitude of stresses all at the same time” sparked the excessive fruit drop.

HLB is the prime cause and has added to the stress, he says.

Trees that showed no signs of greening only had fruit drop of 2 percent to 3 percent per month, he said.

Trees that were infected, yet otherwise healthy and productive, experienced drop of about 7 percent—twice as much as usual.

Infected trees with some decline had drop rates of 30 percent to 40 percent, compared with 10 percent to 15 percent during a normal year.

The Ridge area of Polk County seemed to have more severe drop than the southwest area, possibly due to extremely dry weather, Rouse says.

Two possibilities

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