What is in this article?:
- Researchers, grower finding heat treatments effective against citrus greening
- Different levels of heat
- Results have been striking
• Research work shows that heating potted citrus seedlings in greenhouses kills off the HLB bacterium and can rid the seedlings of citrus greening symptoms.
• Florida citrus grower David McKenzie has been encasing citrus trees in opaque, plastic PVC “tents” to heat them up for about a week, then removing the tents and trimming off the top 10 or 12 inches of the trees that have been “browned up” by the solar heat.
• The results have been striking. Within short periods of time, leaves stunted by HLB begin to flourish, and by the time the fruit is ready for harvest, its quality is noticeably improved.
Results have been striking
The results have been striking. Within short periods of time, leaves stunted by HLB begin to flourish, and by the time the fruit is ready for harvest, its quality is noticeably improved.
“The flush (leaf growth) after the tents are removed is phenomenal. The leaves start to flush about 2 to 4 weeks after the tent is removed, and that flush will peak after about 6 weeks,” McKenzie says.
McKenzie has been using the tents for about a year and a half, applying them from April to September. He has covered about 1,000 of his 130,000 trees, working in alternating 20-acre blocks and tenting about 5 trees at a time in each block.
He selects trees with moderate HLB symptoms (smaller, shriveled fruit and stunted leaves) that are about 3 to 6 years old and 6 feet high.
He uses cinder blocks to hold the tents in place and positions the tents so their tops are near the tops of the trees and they drape closely around the tree circumference. That way, by mid afternoon the heat in the tents reaches about 125 ̊F near the treetops and about 110 ̊F near the base.
“Once trees reach a certain size, maybe to where they have a 25-foot circumference, that’s about the maximum size for using the tent. What is important is for the top of the tent to be close to the top of the tree, so you have heat at the top,” McKenzie says.
Tents can be reused, and McKenzie estimates that with labor, the system costs about $45 per tent. He says the results are worth the effort.
“We’re finding that the trees we tented last year don’t need to be tented this year. Trees with major symptoms before the treatment have minor symptoms after treatment, and the trees are producing normal fruit where they were producing small fruit before,” McKenzie says.
As with the potted citrus, Duan is un- sure about the specific biological causes underlying the results. HLB is a systemic disease, and eliminating it from a tree generally requires eliminating it from the roots. The heat doesn’t entirely kill off the HLB in the tree, but it seems to weaken the infection process and prolong the tree’s productive life.
“It works better if the infection is in its early stages and the bacteria have not yet reached the plant root,” Duan says.
The results of Duan’s field trial at McKenzie’s groves are not yet published. But Duan is promoting them along with the growth chamber results in scientific conferences and meetings with growers and nursery operators. The work has been partially funded by FDACS and the Citrus Research and Development Foundation.
Growers are beginning to consider the approaches, where practical, and McKenzie is enthusiastic about the results.
“Do I think it works? Absolutely I do. It’s encouraging. It makes me think that with all the damage we’re seeing from citrus greening in Florida, we’re staying in the game,” McKenzie says.
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