Enhancement of postbloom fruit drop control measures

Enhancement of postbloom fruit drop control measures

Report Date: 10/03/2018
Project: 16-010C   Year: 2018
Category: Other
Author: Megan Dewdney
Sponsor: Citrus Research and Development Foundation

June 2018 The objectives for this proposal are1) Conduct ground and aerial applications of fungicides to determine the efficacy and economics of fungicide treatments; 2) Determine if Luna Sensation has enough systemic activity to protect flowers from before they fully develop and open; 3) Determine if the period flowering of trees affected by huanglongbing can be narrowed to eliminate the offseason bloom that contributes to the PFD inoculum increase in groves. Trials were conducted to evaluate further fungicides and fungicide programs. We applied 30 treatments in 3 trials at two locations. One site had Navel oranges and the other was Valencia sweet orange. Only one application was made in each site because there was so little rain during bloom. There was rain during bloom but the temperatures were so low during the rain events that limited disease developed and there was one predicted infection event the week of March 7 when using the PFD-FAD forecasting system. Button data from these trials was collected in early June but has not been analysed. Fruit data are expected to be collected in July. Experiments to validate the Brazilian model, now as part of the citrus advisory system (CAS), were carried out in two citrus production areas, one with Valencia and the other one with Navel trees. Treatments were equal to the ones tested in 2017. Due to drier and cooler weather the Brazilian model did not recommend any sprays in both orchards. PFD-FAD-based treatments were sprayed twice, whereas three and two weekly applications were performed in the Valencia and Navel groves, respectively. The difference in number of weekly applications was due to the shorter flowering period of the Navel trees. Button data was collected from these locations in early June but has not been analysed to date. Fruit data will be collected as soon as the fruit are large enough to easily see within the canopy. During this time period, the Valencia harvest and flower count data from spring was analyzed. There was no significant difference in yield were observed as result of treatments. Interestingly, a significant increase in fruit size was observed with GA (20 g a.i.) applied 5 times in season as compared to control and NAA treatment. With the use of GA (20 g a.i.; 5 times), we were able to compress the flowering window and decrease the number of flowering. NAA had no effect on flowering window or number. No changes were made to the web interface of the PFD model, citrus advisory system (CAS) during this period. The manuscript continues to be prepared about the CAS decision support system and will be submitted to the Computers & Electronics Journal when completed. This publication will describe the database infrastructure, system functionalities and applications. The presentation at the annual meetings of the Society of Agriculture Engineers – Florida section in June was done.


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