Fruit left on the ground is a waste for growers and consumers alike, and Florida’s citrus industry certainly cannot afford to leave any fruit behind.
Citrus fruit drop before harvest has been particularly challenging during the 2020-21 Florida growing season.
That is why Fernando Alferez, University of Florida Institute of Food and Agricultural Sciences (UF/IFAS) citrus horticulturist, is researching strategies to reduce the amount of drop from trees prior to harvest. He discussed his preliminary findings during the most recent UF/IFAS OJ Break webinar.
According to Alferez, about 10 to 15 percent of citrus drops from a healthy tree on a normal basis. The pressure of citrus greening undoubtedly increases the chance for drop, through. Depending on the variety, some growers have experienced preharvest drop of up to 50 percent in recent years.
Understanding the physiology associated with fruit drop on HLB-affected trees has allowed Fernandez to develop new tools to assist in controlling drop and improving yields.
“We can modify hormonal balance in the fruit with commercial, feasible treatments applied at the right time,” Alferez says. “These treatments help to alleviate fruit drop and increase yield.”
Researchers found that auxin biosynthesis and signaling were dependent on zinc levels. According to Alferez, zinc deficiencies created increased stress on the plant, leading to growth inhibition, drop and poor fruit overall.
With this information, researchers applied zinc and indole acetic acid (IAA) treatments in Hamlin on Swingle and US-942 rootstocks to test their impact on preharvest fruit drop.
Based on their results, both trials (zinc and IAA) had seasonal effects on drop in the field. Both trials saw less fruit drop when the treatments were applied in June and October, but an August treatment resulted in increased drop.
“The timing of application is critical for treatment success,” Alferez says. “This must be defined for each variety and treatment and depends on the physiological status of the fruit.”
In the second year of the trial, researchers saw encouraging results on yield. Hamlin trees on Swingle rootstock saw an increase of 25 boxes per acre undergoing zinc treatments. Hamlin trees on US-942 rootstock saw an increase of 19 boxes per acre undergoing zinc treatments.
“We have a lot of work to do. But, by understanding mechanisms of fruit drop, we have found a path forward. Expanding our knowledge on these mechanisms will lead to additional paths for success,” Alferez says.
To participate in upcoming UF/IFAS OJ Break meetings, register here.
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