California Pistachios: Kern County Signaling Great Winter Rest Period

I visited a trial located in the citrus belt in what I consider a “low-chill” area of Kern County (near the intersection of Highways 65 and 155) on March 13. The flower buds of Golden Hills, Lost Hills, Kerman and Peters still looked dormant on this date. However, the early-blooming males and female trees in this trial were 12 days ahead in bloom compared to last year.

Earlier bloom, usually, signifies that winter chilling was better. Bloom, on the south side of these early-blooming cultivars, was ahead of the north side, which I have not seen anywhere in a number of years. This observation suggests that the trees’ winter rest period was met completely.

When this happens, the tree knows winter is truly over and triggers flowering, and since the south side is warmer than the north side, the south side leafs out and blooms earlier. In low-chill years, typical for that last seven years of so in Kern County, bloom on the north side of the tree is ahead of the south side.

I have been sent pictures (on March 16) from the Buttonwillow area, where problems with inadequate winter chill, usually, are fewer. In these pictures Kerman and Peters trees, already, are beginning to leaf out and flower buds are beginning to swell. This is extremely early, even by our old standards when better chill was the norm.

From these pictures sent to me, Peters’ bloom looked to be ahead of Kerman, which used to be common in the 1980’s, 1990 and early 2000’s before our fog went away. Years like these reinforce the notion that we want to have more than one pollinizing cultivar in our pistachio orchard.

For most orchards, the 2020-21 crop season is going to be an “on” year in the alternate bearing cycle, although, perhaps not as “on’ as it would have been had we not had a great-yielding “off” year last year. The news that the winter rest period was good, strongly suggests that we are in line for a very high-yielding year.

Good chill, also, tends to syncronize the bloom and the harvest across the different growing areas of California. Perhaps the biggest production cloud on the horizon then, aside from not knowing how the navel orangeworm will affect the crop this fall, is the upcoming challenge of harvesting a huge crop with existing equipment and processing facilities within a potentially tighter harvest window.




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