Combating Postbloom Fruit Drop

Citrus greening has certainly taken center stage when it comes to combating diseases in Florida’s citrus groves, but Postbloom fruit drop (PFD) is one disease that citrus growers cannot afford to overlook. PFD is a fungal disease that can cause anywhere from 20% to 80% fruit drop in a grove, depending on the severity of the infection. Once a flower is infected, the fruit is sure to fall o shortly after developing, and there is no option to save it. PFD is a tricky disease to treat for a number of reasons. The spores that cause PFD live and reproduce on the leaves, twigs, and buttons—or calyces le over from infected owers—and they travel by rain. Increasing winter rains generally lead to a higher rate of PFD infection during flowering and fruit set. Everyone in agriculture knows you can’t control the weather. PFD is generally treated with fungicides, but there are many issues with this as well. Treatments must begin early and continue with reapplication a er rainy conditions. However, the fungicides used are detrimental to pollinators, are viewed negatively by consumers many are limited by government regulations, and PFD is developing a resistance to those fungicides that are most commonly used. is ties growers’ hands with what fungicides, and how much, they can use to combat PFD. As a solution, some companies have created formulations that activate a citrus tree’s own defense mechanisms, called systemic acquired resistance, or SAR. The product is sprayed on the citrus trees, and it elicits the tree’s defense mechanism to form specific defense proteins to combat PFD from within. Studies have shown that the use of such SAR-inducing formulations can lower the incidence of PFD by 48% when compared with a non-treated control. One product still under development, Keyplex 1000, is touted to lower PFD incidence by 70%. Many of these formulations also include foliar fertilizers containing uptake additives and minor nutrients to help citrus trees through the stress of fruit development. They can also be mixed in-tank with fungicides to improve uptake and allow growers to tailor their PFD management strategies.

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