Bioregulators have been used for many years to alter the behavior of fruit or fruit trees for the economic benefit of the fruit grower. Control of vegetative vigor, stimulation of flowering, regulation of crop load, reduction of fruit drop, and delay or stimulation of fruit maturity and ripening are important examples of processes in fruit and fruit trees that can be regulated with exogenous applications of bioregulators. New candidate bioregulators with possible benefits for fruit growers are continually being made available by private industry. In addition, we are continuing to find new uses for bioregulator products that have been made available for other uses. In our research program we seek to develop information that can help Washington tree fruit growers to benefit economically from the use of bioregulators in the orchard and nursery. Examples of program directions and effects are described below.
Mechanical Harvesting of Sweet Cherry
The sweet cherry industry in Washington has doubled in acreage in the past 10 years. The potential for labor shortages at harvest in the next few years is highly likely. Mechanical harvesting is routine in many processed crops but has not been widely adopted for fresh-market production of tree fruit. One key to successful mechanical harvesting of sweet cherries is the capacity to loosen the fruit sufficiently to permit their easy removal from the tree by shaking limbs. Loosening of sweet cherries has been accomplished by applying ethephon a week or two before harvest. Unfortunately, ethephon also stimulates the softening of the fruit flesh, making the cherry more susceptible to damage during the handing and marketing process. Recently we have discovered that preharvest application of the bioregulator 1-methylcyclopropene (MCP), used commercially to control the ripening of apples and pears, may control fruit quality loss of ethephon-treated fruit without affecting fruit loosening.
If bioregulators can be effectively developed to loosen sweet cherries without reducing quality or shelf life it opens the window of oportunity to save the industry millions of dollars in harvest costs while facilitating the profitable expansion of sweet cherry production in Washington.
Control of Alternate Cropping in Apple
Alternation in cropping from year to year has always been a problem in apple production. Chemical thinning techniques have been used for half a century to address this problem but with limited success. Removal of young fruitlets alone is not always sufficient. We are evaluating the use of gibberellic acid (GA) as a technique for reducing flower formation in the low crop year to see if the alternating cycle can be effectively interrupted with a combination of flowering control in the low crop year and good thinning practices in the high crop year. We have found consistent reductions in flower formation in the ‘Fuji' cultivar when GA is applied shortly after flowering. Testing is underway in other cultivars.
Evening out cropping from year to year would greatly benefit the profitability of the tree fruit industry by diminishing the impact of reduced prices in heavy crop years and improving returns to more growers in what would have been light crop years. The use of bioregulators to reduce biennial bearing appears promising at this time, but much more work is necessary before it can be recommended for commercial practice.
Stimulation of Lateral Branching in Young Trees
Proper branch development is a critical feature in the care of young fruit trees. Good branch development begins in the nursery and continues in the orchard. Techniques for effective stimulation of branch development that avoid pruning could shorten the time needed to develop a fruitful canopy. Dr. Elfving's research discovered the lateral branching potential of a new candidate bioregulator, cyclanilide®. This product effectively produces excellent lateral branch development in apple, pear and sweet cherry trees. It can be used in the nursery as well as the orchard.
Branched trees from the nursery crop more quickly when planted in the orchard. Improved branching and more rapid canopy development could significantly reduce the time required for new orchards to amortize their establishment costs. This single fact would return more dollars earlier as profit to the grower, and that benefit would continue over the life of the orchard.
Don Elfving, Horticulturalist
Tree Fruit Research & Extension Center, Wenatchee
Office Ph: 509-663-8181 x252
Office Hours: by appointment