UC Cooperative Extension Ventura County
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Ventura CA 93003
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Adjusting to a Smaller Fruit Load - 2000
This past spring with its cool temperatures has generally meant a poor fruit set for the avocado industry. Walking orchards in the Santa Barbara/Ventura area turns up trees with little or no fruit set. There tends to be more fruit in areas further from the coast and in perimeter trees of an orchard where more light, warmer day time temperatures and probably more access was available to bees. The question now is what sort of fertility plan one follows in this situation. If one is diligent in taking early fall leaf samples, how will the fruit load affect an interpretation of those analyses?
A leaf (tissue) analysis integrates the tree's environment - sun, temperature, water regime, soil conditions, fertility management and fruit load. The higher the fruit load, the more nutrients are diverted into the fruit. The less fruit, the more of the nutrients go into vegetative growth, and consequently a larger tree. Big, ranging trees are already a problem in the industry and not paying attention to fertility management this year can exacerbate the problem.
A point to remember is that a leaf analysis is integrating the management practices and fruit load of the previous year. It was the fertility program of the previous year that is determining the leaf analysis along with all the other cultural and environmental factors. So if a grower continues fertilizing in a similar fashion as was done in the previous year and there is a low fruit load, this will encourage more leaf growth. More leaf growth to cut out at a later date. If tissue analysis this fall shows adequate or high levels of especially nitrogen, then applications should be curtailed by 10% or more.
Controlling applications is especially true for those who have taken advantage of the low fruit set to stump or scaffold trees. In this case the trees have a huge root system to mop up nitrogen and continuing on the old fertility plan will just encourage rank new growth, which will just mean more management. Continuing to feed on the old plan just means more hay to cut. In the case of stumping, a tree may not need nitrogen until flowering commences again. In the case of scaffolding, a reduction of 50% of the previous application is warranted.
With less fruit on the trees it is easier to make a decision to follow a pruning pattern this winter of selective branch pruning to reduce the size of trees and open the canopy to light. In the process some of next year's bloom will be removed. With a low yield from this year's set, there promises to be a heavy bloom next spring. If there is good weather for fruit set there promises to be a heavy fruit set. Bloom and fruit set drain heavily on the energy of the tree. Removing some of the bloom through branch pruning will alleviate some of the stress.
In South Africa, Stefan Kohne has demonstrated that in years of heavy bloom, the competition for energy from the bloom can be so great, that fruit set is reduced. He advocates removing a substantial amount of the bloom in order to allow energy to go into fruit set of the remaining flowers. In the process of bloom pruning, the tree is also reduced somewhat in size. This would not be the primary pruning method, but an additional practice along with regular tree canopy management.