Search Beesource.com



Winter Weather Affects Almond Yields

by Joe Traynor

California almond growers are basking in the glow of two consecutive years of record-setting yields: 2650 lbs/acre in 2011 and (although the final tally isn’t in) close to that in 2012. Quite an accomplishment considering the average crop for the 10 previous years was 1936 lbs (the previous record was 2400 lbs. in 2008).

The record crop this year can be explained by the almost perfect weather during bloom, the best most growers can remember. But how to explain the record 2011 crop – when bloom weather was the worst that most growers can remember?? Recorded bee hours (temperatures above 55 degrees F, no rain, and winds below 15 mph) was the best ever in 2012 and maybe the worst ever in 2011 (for the 10+ years that bee hours have been recorded; old-timers will tell you that the worst-ever bloom weather occurred in 1958 — rain throughout bloom resulted in a record-low crop of around 200 lbs/acre) The record 2011 crop is difficult to explain because it flies in the face of the long-held belief: that bloom weather determines the almond crop. Growers that regularly beef up bee colony numbers in case of poor bloom weather probably patted themselves on the back after the 2011 season – but growers that stuck with 2 colonies per acre (or even 1 colony/acre) also got excellent yields in 2011.

As many have pointed out, a strung-out bloom in both 2011 and 2012 gave more overlap of bloom between varieties and gave bees more time to completely pollinate a given almond orchard, resulting in higher yields both years. An associated phenomenon, probably just as important, is that a strung-out bloom results in a wide range of maturity of post-bloom nutlets on any given variety – from pea-sized all the way down to tiny nutlets barely visible after petal fall.

In a year of compressed bloom (sometimes referred to as a flash bloom) there is little variation in post-bloom nutlet size. Developing almond nutlets put on a tremendous growth surge during the few weeks following bloom. This rapid surge in nutlet size, in turn, puts a tremendous draw on a tree’s carbohydrate and nutrient reserves – trees compensate by shedding nutlets. (A crueler version of post-bloom nutlet drop occurs in the animal kingdom when a litter – of pigs, ducks, cats, etc. — is too big and one or more individuals are abandoned by the mother because they outstrip her resources). A strung-out bloom, gives a wide range of nutlet sizes, spreading out the demand on a tree’s resources and allowing more nuts to reach maturity. This is what happened both in 2011 and 2012.

To confirm the above thesis, one has only to look at the Fritz variety, a prolific setter of nuts, year-in and year-out. Unlike other varieties, Fritz nutlets grow very, very slowly from petal fall through April – Fritz’s draw on a tree’s reserves is both gradual and minimal during the critical post-bloom nutlet drop period. The bumper crops that Fritz sets every year – “them trees are loaded!” – is tempered by Fritz’s smaller nut size at harvest. If other almond varieties held a set like Fritz does, we’d see more 5000 lb/acre yields than we do now.

Two important ingredients determine whether we will have a compressed bloom, or a strung-out bloom: winter chilling hours and winter fog. Compared to other deciduous tree crops, almonds have a modest chilling requirement – 200-350 hours below 45 degrees F – an amount easily satisfied in most years, if not every year. The wild card is the amount of valley fog during the winter. Foggy days were minimal during the winters preceding both the 2011 and 2012 seasons. Although the days were cool, sunny afternoon temperatures heated up bark and buds, more so on branches exposed to sunlight than on shaded branches. A UC study in the 1970s (on peaches) found that on a sunny winter day, exposed bark temperatures were 36 degrees higher than air temperatures and that the shaded parts of trees had significantly lower temperatures than branches exposed to sunlight. Sunny winter days, regardless of air temperature, undoubtedly offset a portion of accumulated chilling hours, and result in flower buds of differing stages of development – setting up a strung-out bloom. (Chilling hours for cherries and pistachios in the Southern San Joaquin Valley can be marginal and growers of these two crops should consider white-washing their trees during the winter to offset high bark temperatures during sunny days).

Winter fog in our Central Valley has been called “the billion dollar fog” for its role in satisfying the chilling requirements of fruit and nut crops. Almonds may be the exception to this rule. A cold, foggy winter will result in a flash bloom, and even if the bees did their job during such a bloom, the draw on a tree from all those nutlets sizing at once could well result in an excessive drop of pollinated nuts.

With the idea of man-made global warming becoming increasingly accepted (even by former skeptics – you’ll know its game over when Rush Limbaugh, if he lives that long, announces “I’ve been wrong about global warming, folks …”) almond growers may not have to worry about excessively cold winters. Their concern could well switch to winters that fail to satisfy the minimal chilling requirements of almonds. In such a case, it might be prudent for California almond growers to stake out almond ground in Canada for their grandchildren, or to bone up on the cultivation of macadamia nuts and mangos if they decide to remain in California.

_____
This article appeared in the November 2012 issue of Pacific Nut Producer