Plant
Bioregulators
Don Elfving, Horticulturalist
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.