2008 Annual Report
Treatment of longan with potassium chlorate often results in 100% flowering terminals which results in smaller fruits. We have conducted experiments to determine the optimal amount of the panicle that must be hand thinned to maximize fruit size and total harvestable fruits per tree. ‘Biew Kiew’ trees were treated with 250 g of potassium chlorate. When fruit reached “pea-size”, longan panicles were thinned to remove 0%, 25%, 50% or 75% (10 panicles per treatment) of the developing fruit. The number of fruits per panicle was recorded during treatment implementation. The remaining panicles were thinned to remove 2/3 of the fruits. No significant difference was detected in the fruit size and weight for the fruit thinning panicles suggesting the overall fruit load per tree may be more important than thinning individual panicles. Experiments are currently being implemented to determine if foliar fertilizers can replace the labor intensive hand-thinning procedure. Harvested fruits from foliar and hand thinned trees will be provided to another project which will be evaluating postharvest quality during storage.
In Hawaii, consistent lychee production is achieved through management practices that limit high nitrogen content and new vegetative flushes during the time of year when cooler temperatures induce flowering. We have adapted the pruning and foliar management protocol developed at the TPGRM unit and expanded it to commercial 'Kaimana' fields located in the rocky soils of Kona and deep silty clay loam soils in Hamakua. The pruning and foliar fertilizer application successfully resulted in flowering and fruiting of lychee in Kona similar to the trees in the TGRMU lychee orchard. However, the pruned and foliar fertilized trees resulted in vigorous vegetative growth and reduced flowering and fruit production in the Hamakua orchard. The best treatments for this location were non-pruned control trees and non-pruned trees treated with foliar fertilizer only. These experiments will be repeated at the various locations for the next lychee season. In addition, plants have been propagated to determine the temperature requirements for floral induction of ‘Kaimana’ lychee through growth chamber experiments.
Application of foliar fertilizer instead of ground applied granular fertilizer to producing ‘Kaimana’ trees after pruning provided consistent levels of nutrients to the trees, reduced reliance on fertilizer availability dependent upon rainfall and limited the amount of residual fertilizer held in the soil. An average production of about 100 lb per tree per year occurred over two seasons in 8-9 year old trees when pruning and foliar fertilizer was used to synchronize and condition 'Kaimana' lychee trees at the Waiakea Station. This pruning and foliar management protocol at Kona and Hamakua orchards resulted in successful flowering and fruiting in Kona similar to trees at Waiakea. However, treatments in Hamakua resulted in vigorous vegetative growth and reduced flowering and fruit production. The pruning/foliar treatment was most promising in orchards with rocky soils and little water holding and nutrient retention capacity.