UF/IFAS research indicates that zinc and potassium may combat fruit drop for Florida citrus growers according to a presentation at the Florida Citrus Show.

Fruit drop has been a real problem for Florida citrus growers, and the combo of citrus greening has exacerbated the issue. A UF/IFAS research team presented findings during the Florida Citrus Show of a three-year study with results showing that zinc and potassium might combat fruit drop, according to a Citrus Industry article. See the details below.

Zinc and Potassium Foliar Applications

The study looked at the impact of foliar applications of zinc sulfate and potassium sulfate on fruit retention and yield. It utilized three different application times—after fruit set (early June), fruit enlargement (July), and color break (September)—on Hamlins and Valencias.

During the presentation, Fernando Alferez, a UF/IFAS assistant professor of citrus horticulture, said “We know from research literature and by observing other plants that zinc deficiency produces in plants two main things — oxidative stress and impairment of auxin signaling within the plant. We know in the case of several fruit crops, including citrus, that this produces fruit drop. In HLB-affected trees that are experiencing many stress factors, this deficiency can cause even more drop. We made applications to restore the zinc deficiency to improve oxidation and improve the auxin balance. The results show we could improve fruit retention with these foliar zinc applications. As for potassium, we observed improved fruit size and quality, and we know better-sized and quality fruit tends to hold on the tree better.”

According to Alferez, the second and third years saw a yield increase of 22% and 31%, respectively, in the plots receiving zinc plus potassium foliar applications when compared to the control plot. Further research is being planned.

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