By Tripti Vashisth
Hurricane Ian caused extensive destruction on the Florida coast and inland, in both urban and rural areas. The state’s citrus groves had to sustain hurricane-speed winds and flooding.
HLB-affected trees undergo a lot a stress, and now the hurricane has added more abiotic stress to trees. High-speed winds caused significant fruit drop and leaf drop.
The goal now is to retain as much fruit as possible and rejuvenate citrus trees for healthy vegetative growth. However, the fruit and leaves that escaped the drop during the hurricane event are still quite likely to fall in subsequent days.
For retaining fruit, use of 2,4-D and gibberellic acid (GA) is suggested. Both of these plant growth regulators (PGRs) have potential to improve fruit retention and counteract ethylene (the hormone that is known to cause leaf and fruit drop). The efficacy of these PGR applications will depend on the extent of damage that has happened. Nonetheless, these are viable alternatives for growers under current conditions.
Growers are encouraged to apply GA as soon as possible and preferably repeat the application. Last year, researchers saw good results with combined GA and 2,4-D application (three applications from October to December) on fruit drop reduction in Valencia. The current usage label for 2,4-D is not labeled for such use. However, growers are encouraged to make at least one 2,4-D application as per the label. These PGRs should aid in fruit retention.
Excessive leaf loss with good soil moisture content is likely to induce new vegetative growth. However, the abiotic stress from the hurricane and biotic stress from HLB infection may interrupt the potential growth. Therefore, use of GA to boost vegetative growth is suggested. In the groves where the fruit loss has been close to 100%, growers should still consider a GA application to boost vegetative growth.
In addition, use of foliar fertilization with nitrate is suggested to aid with leaf growth. Use of potassium nitrate can be considered for late-maturing groves. Potassium can help with fruit growth, and nitrate can boost vegetative growth.
Tripti Vashisth (tvashisth@ufl.edu) is an associate professor at the University of Florida Institute of Food and Agricultural Sciences Citrus Research and Education Center in Lake Alfred.
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