UF/IFAS experts maintain that Florida citrus growers will likely see melanose in citrus due to the freezing conditions earlier in the year.
“The recent freeze events of the last few weeks have scrambled the plans of citrus growers,” shared a UF/IFAS Tip of the Week article, adding that melanose is “one disease that is highly likely to be worse than in other years.” The article shared that “melanose is likely to be damaging even to oranges and other cultivars that do not usually see harmful levels.” See the details of the disease—and how to treat melanose in citrus—below.
How Melanose Affects Citrus
The article shared that “After a freeze, young fruit can split from mudcake melanose. When the rind is badly damaged by melanose, it can no longer expand as the fruit grows.” Melanose in citrus means fruit that is unusable.
Spotting Melanose
The article maintained that “The fungus responsible for the disease, Diaporthe citri, produces spores on dead twigs under 1/8 of an inch. These twigs can be colonized by the fungus two ways: 1) as young alive twigs or 2) after the twigs have died. The small twigs are vulnerable to damage from extreme cold. Once it is warmer, these twigs can be colonized by fungus and produce abundant spores.
While the current forecast is for lower than average rainfall in Florida during the spring, this is not necessarily relief from melanose. The fungus can viably store the spores for a month in a paste that looks like it has been squeezed from a toothpaste tube. When a rain event occurs, large numbers of spores are splashed onto vulnerable leaves and fruit, where they cause large areas of symptoms.”
Treating Melanose in Citrus
“Copper is still the most economical product for managing melanose,” the article advised. “The first application is usually in mid-to-late April, with the timing depending on predicted rainfall. Copper should be in place before rain events, or it will be ineffective. Applications should be every 21 days with a rate of 0.7 pounds per acre of metallic copper. Most oranges and tangerines should be adequately protected with one or two applications. Grapefruit should be protected until the fruit are 3 inches in diameter, usually by late June or early July.”
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