Citrus canker could spread in Florida groves as a result of Hurricane Milton, researcher Megan Dewdney warned. A University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) associate professor of plant pathology, Dewdney offered suggestions for dealing with canker at a recent UF/IFAS hurricane recovery webinar.
WIND WOUNDS
High winds and rain, which were abundant during the hurricane, move canker-causing bacteria, Dewdney said. Winds cause wounds in the canopy — including ragged leaves, thorn punctures and scoring of leaf surfaces — that are vulnerable to infection. Winds higher than 18 miles per hour push canker-causing bacteria past any protective coating. Tissues that are otherwise not susceptible to canker can become infected under storm conditions.
Dewdney said it is too soon to see infections resulting from the storm. Most Florida fresh market fruit has reached the developmental stage that is immune to canker infections, but grapefruit may be an exception. Growers worried about possible infections should scout carefully, she suggested.
Dewdney warned that copper protection against canker on fruit will have been broken by Milton’s high winds.
COVERED CITRUS
If citrus under protective screen (CUPS) structures were damaged by the hurricane, canker could enter through rips in the screen and could be dripped to small numbers of trees from the roof, Dewdney cautioned.
She added that individual protective covers (IPCs) normally protect young trees from canker, but that more canker was seen on the windward side of trees inside IPCs following Hurricane Ian in 2022. The bacteria had been forced in by wind and mostly affected foliage.
Dewdney suggested actions to take against canker following the hurricane. She said growers worried about defoliation (badly affected leaves are likely to drop in the spring) can apply copper, but it’s not likely to be useful in processing orange blocks.
TOP CONCERN: STEM LESIONS
The greatest canker concern following Milton is stem lesions in young trees, the researcher stated. Stem lesions can leak bacteria for up to four years, providing inoculum for future seasons and leading to fruit drop. The lesions, which can be difficult to see, may be pruned out if trees are small.
Plant immune system stimulators can minimize the impact of stem lesions, Dewdney said. They can significantly reduce leaf lesions in young trees and reduce inoculum for following seasons. Two products are available: Actigard (formerly Blockade), a drench, and Aura Citrus, which can be foliar applied during major flushes up to four times a season. Aura Citrus treatments can begin in the fall.
In addition to canker, Dewdney discussed other disease concerns during the hurricane recovery webinar.
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