Florida Citrus Groves Under Siege From Postbloom Fruit Drop
The notion that anything would knock HLB out of the headlines in the Florida citrus industry is hard to believe, but postbloom fruit drop (PFD) has grabbed the attention of growers across the state. For the past three seasons, the ailment has come back and is epidemic in some groves.
While HLB clearly enhances PFD, the problem, caused by the fungus Colletotrichum acutatum, has been around for a long time, being first formally described in Belize in 1979. The fungus will infect flowers of all species of citrus, creating orange-brown lesions in the blooms. The fruitlets will then drop leaving buttons behind. In more normal years, PFD effects Navel and Valencia, however this past season, Hamlins also were impacted.
According to the 2016 Florida Citrus Pest Management Guide, most spores of the fungus are produced directly on the surface of infected petals.
Spores are dispersed by rain to healthy flowers where they infect within 24 hours and produce symptoms in four to five days. The fungus survives between bloom periods as resistant structures on the surface of leaves, buttons, and twigs. Flowers are susceptible from the pin-head stage (with white tissue present) until they are open.
HLB’s involvement comes with erratic bloom it has triggered in citrus trees, which makes it more difficult for growers to time fungicide applications for maximum efficiency.
“HLB causes the tree to flower all year,” says Megan Dewdney, Associate Professor of Plant Pathology with UF/IFAS. “In nearly every block, there will be flowers somewhere. There is enough to keep the fungus active and ready to infect the next set of flowers.”
Conditions were ripe for PFD during the past three seasons’ main bloom, with each passing season building up more inoculum. The El Niño weather pattern brought rain during bloom, which grows and spreads the fungus.
Henry Yonce, Owner of the consulting firm KAC Agricultural Research, says PFD was as bad as he has ever seen this past season.
“The PFD was severe in Navel and Valencia this season,” he says. “It was by far the worst I’ve seen in citrus, and I have been working in Florida since 1984.”
Yonce heard of one Valencia grove in the Immokalee area that picked 600 boxes per acre two seasons ago. The same grove picked 150 boxes this season, and the grower reports the PFD was so severe there might not even be enough fruit to spray for next season.
“Last season was particularly bad because bloom lasted in some cases from November through April because of the lack of cold weather over the winter,” Dewdney adds. “There were two seasons of inoculum built up in those trees.”
USDA’s first forecast for the 2016-2017 Florida orange season will be __________ 80 million boxes.
- Less than (78%, 145 Votes)
- Greater than (12%, 22 Votes)
- Equal to (10%, 19 Votes)
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While PFD has historically not been a problem in Hamlins, growers did report problems last season. Yonce adds growers better be vigilant for drop next spring in bloom, even in Hamlins.
“The Hamlins have not really been susceptible to PFD in the past, but there is so much inoculum out there right now, we are seeing it show up in other varieties like Hamlins and tangerines. It is starting to get a foothold in these varieties, so if we have rainfall next year in bloom, I would recommend spraying Hamlins.”
In late June, the Citrus Research and Development Foundation hosted a special meeting of its Research Management Committee to hear from a cross-section of scientists with experience in PFD. A summary of that meeting is available from the Foundation at Citrusrdf.org.