Weak Flowering/Leaf Out in 2021

There have been several reports of poor bloom, slow leaf-out, and general lack of spring vigor from several orchards within California. Traditionally, when this occurs, many assume it is due to higher than anticipated yield, leaf drop due to disease, or poor post-harvest irrigation practices. Although these causes will affect individual orchards on any given year, it doesn’t seem to match the general occurrence of these symptoms observed across the State.

In trying to diagnose the issue, we have to look back to the postharvest period of 2020. This period is when the tree stores energy for the next year’s fruiting cycle. As most of us remember, it was a summer filled with gray to black skies, humid weather, and general poor air quality due to smoke from the various fires. Could the smoke have caused the declines in productivity that many are seeing this year?

History has shown that this is a possibility. Major volcanic eruptions in the past have led to cooling events due to smoke and ash in the atmosphere. This ash reduces the amount of light that is intercepted by plants, leading to lower production. Examples include the eruptions of Mount Tambora and Laki volcano which have been associated with the European famines of 1816-1819 and 1783-1784, respectively.

This may seem like a far reach, but is it? Smoke is known to reduce red and blue wavelengths within light. These are the two primary wavelengths that plants use for photosynthesis. If the smoke impacted the amount of energy produced by the almond tree during the postharvest period, it would reduce the amount of stored energy for the following year’s bloom. Results from carbohydrate extractions from almond wood provided by the Carbohydrate Observatory  show exactly this. Data collected from orchards across California show that the average stored carbohydrates in the postharvest period of 2020 was the lowest observed in the past five years (figure above). Furthermore, these measured amounts were significantly lower than fall carbohydrate levels from previous large cropping years (2017, 2018). This data indicates that the trees entered 2021 with less stored energy, which could have been the cause of the weak protracted flowering, early but slow leaf-out, and poor crop set.

In some ways, this may seem crazy. I don’t think it is. History has shown that environmental catastrophes may impact future crop production and localized data supports this hypothesis.

Thoughts?

Due to the value of the work conducted by the Carbohydrate Observatory, pledged Patreon funds exceeding the operational costs of "The Almond Doctor" will be donated in 2021.