Reducing fruit drop by altering hormonal responses within the tree through nutritional and hormonal therapies: a mechanistic affordable approach

Reducing fruit drop by altering hormonal responses within the tree through nutritional and hormonal therapies: a mechanistic affordable approach

Report Date: 02/14/2023
Project: 21-007   Year: 2023
Category: Horticultural & Management
Author: Fernando Alferez
Sponsor: Citrus Research and Development Foundation

1. Please state project objectives and what work was done this quarter to address them: Specific objectives are:1) To determine the right timing for Zn and K treatments to minimize fruit drop.2) To determine effects of GA3 and 2,4D applications on fruit retention when applied at different times during fruit development.3) To develop a strong and proactive outreach program.  For objective 1 we harvested Hamlin on the first week of January, 2023. As a reminder, we performed treatments at three different dates: on early June 2022, a second set of treatments by the end of July, 2022, and a third set by early September 2022. Every set of treatments was performed in an independent block, so treatments are applied only once, to assess the best timing to achieve the best results. Results for this first season, seem to confirm our hypothesis that only one treatement of Zn and Zn+K, done at the right time, may increase even more the yield. these are the data for the first year:In Kg per 3 trees, control was 67,8, Zn+K applied in June was 70.3 (4% increase, not significant at p<0.05), Zn+K applied by the end of July was 83.9 (25% increase, significantly different), and Zn+K applied in early September was 105,4 Kg (57% increase, statistically significant at p<0.05).These are encouraging results, especially considering that  Ian hit in late September and we had massive fruit drop (around 75%) in the SW FL area. We expect that these data will improve next season. So far we see that only one treatment performed in September can be enough to have a susbtantial increae in yield, although we should confirm this next year, hopefully without the background noise that a hurricane imposes. Treatments only with Zn or K also yield statistically significant better returns, but not as remarkable as the combined Zn+K treatment.  For objective 2 we also found better yields with combined application of GA and 2,4 D. The repeated application of GA and 2,4 D yielded 180 lb/tree as compared to 142 lb/tree in control (p value =0.1). Due to shortge in supply of GA and 2,4 D, the first application of GA was made in July and in August for 2,4D. Altogether tree received 3 GA and 2 2,4 D application in entire season. No effect of GA alone or 2,4 D were seen.  Objective 3:- F. Alferez, ASHS invited webinar on fruit drop mecanisms. January 12, 2023. - F Alferez, Combining IPCs and brasinosteroids in citrus & increasing yield by using Zin. An update. Citrus Production School, February 9, 2023 in Arcadia.-Vashisth,.T. Use of PGRs to improve citrus proiduction, January 12, 2023 in Polk OJ Break 2. Please state what work is anticipated for next quarter: In next quarter,  we will continue treatments now in Valencia for objective 1 and 2  we will start assesing fruit drop in this variety. We will also collect samples for analysis and assess flushing, blooming, and fruit set in both varieties.    3. Please state budget status (underspend or overspend, and why):Spending is now on track.    


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