Freeze damage to Florida citrus could lead to a buildup in certain diseases. One, in particular, is a major threat, believes Megan Dewdney, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) associate professor in plant pathology and Extension specialist.
“Our big concern in terms of foliar problems is going to be melanose. Just as a reminder, melanose produces all of its spores that are really important for the disease, year to year, on dead wood thinner than a pencil,” said Dewdney during last week’s post-freeze seminar hosted by the UF/IFAS Citrus Team. “This is a fungus that knows its environment and saves up its spores if there’s no rain. It’s capable of storing those spores for over a month in dry conditions.”
According to UF/IFAS, grapefruit is the citrus variety most vulnerable to melanose. The disease is especially significant in years which freezes cause large amounts of dead wood in tree canopies because the spores are produced in fungal structures on the dead twigs. That has been the case following the freezes in late January/early February.
Fruit is susceptible to melanose from fruit set until late June or early July.
“When we get rain, we’re going to have significant melanose. If it’s poorly timed, in terms of you’ve got young fruit on the tree, then all of that inoculum has the potential to hit your fruit,” Dewdney explained. “As those poor fruit try to grow, with the amount of melanose, you’ll see mudcake symptoms where the whole surface is scarred. Fruit will crack and be lost.
“We don’t want to see that. We want to try to get those fruit protected. However, we don’t want to do it too far out in advance, because as the fruit grow, that protection gets cracked with the copper. It’s a balance of keeping an eye on the weather and making sure you can get your equipment into the grove at an appropriate time.”
Learn more about postfreeze citrus disease management here.