Varietal Bloom Issues

Weak bloom experienced in an orchard:
Nonpareil and Monterrey shown.

I have received more calls about weak bloom on almond pollinators. These trees have low counts of fruit bud, and the vegetative buds have pushed giving the tree a green instead of white appearance. The reports have been coming in from orchards of “juvenile orchards” (7-10 years of age), which typically have yielded quite heavy for their age. Nonpareil is affected, but the later harvested varieties, which include Monterrey and Fritz, are affected more severely.  

In being in these orchards, it is clear that the period of fruit bud development was affected sometime last year. Fruit bud development/floral initiation varies among varieties. Studies have shown that ‘Nonpareil’s’ fruit bud differentiates about 7-14 days after harvest, while other varieties, such as ‘Carmel’, the majority of fruit buds differentiate prior to ‘Carmel’ harvest. This timing will be delayed in cool, mild years. Tree stressed imposed during this period will reduce fruit bud set, and the buds will remain vegetative (leaf buds).

Very fruit bud are found on the trees,
the majority of the buds are vegetative (leaf).

In regards to the weak bloom, working with the farmers, we were able to identify some of the possible stressors that may have occurred during the period of fruit bud differentiation. Although we are unsure of the exact problem(s), the ones we are considering include:
1. Holding back of irrigation in order to “force” hull-split or harvest,
2. Excessive foliar disease, including rust or scab, that caused defoliation,
3. Improper nutrient management – usually very low potassium and boron, and
 4. heavy yields that reduced the vigor of the tree, impacting growth and the number of fruiting spurs available for future crops.

In many cases, more than one of these issues could have affected the orchard. In orchards that experienced defoliation to foliar disease, many times these trees refoliated in the fall. This growth, although healthier for the tree, reduced the number of fruit bud for the coming spring since these buds reverted to vegetative buds, pushing leaves.

Any thoughts?  

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