Spurs have been around for a bit with early examples used by the Roman Legions of Julius Caesar and more contemporary versions used by cowboys throughout the West.
There’s another type of spur found in the West, this one located in almond orchards where more than 80% of the almond crop is carried on those short, compact vegetative shoots called spurs. Each season a portion of that spur population, borne on the prior season’s wood, is responsible for fruit production.
In a research study on spur behavior published in Tree Physiology magazine, one of the authors, Bruce Lampinen, Cooperative Extension Specialist at University of California, Davis, wrote: “In mature orchards, the majority of the crop is borne on those short, proleptic shoots that can live for several years and produce from one to five fruits.
“Previous year spur leaf area is strongly related to spur viability and flowering — the greater the leaf area in the previous year, the higher probability of spur survival into the next year as well as a higher probability for the spur to bear one or more flowers.”
In a UCCE San Joaquin Valley Tree and Vine treatise on the subject, Lampinen and UCCE Farm Advisor Elizabeth Fichtner noted: “Spurs supporting high leaf area in a given year have enhanced potential to support flowering and nut set in the subsequent year. In the interior of the canopy, non-bearing spurs in lower light positions may require more years in a vegetative state prior to supporting flower and fruit production.”
Spurs remain viable for 3-5 years with their survival potential dependent on light exposure, bearing status, and prior season leaf area. According to the authors: “Promoting modest annual growth allows for production of new spurs which may take a couple of years to support flowers. In managing tree canopies, dead wood and overlapping branches should be removed to prevent shading and promote spur survival and productivity.”
According to an Almond Board of California posting on almond trees, orchard yields “are dependent on maintaining a healthy population of spurs. Although spur death is a given and annual replacement is essential for future production, spur mortality and productivity are functions of previous year leaf areas.
“Spur extension growth and spur leaf growth occurs right after bloom while shoot extension growth that provides new sites for renewing spur populations occurs during the period of growth in the two months after bloom.”
Organ of interest
In a presentation on Tree Physiology, UC Davis plant pathologist Maciej Zwieniecki referred to spurs as the organ of interest in almond population dynamics. “While most people think about the managing of the orchard when it comes to growing almonds, it’s really about managing productive spur populations,” he explained. “At orchard maturity, most almonds are produced on spurs so maintaining healthy spur populations is the key to high yields.”
The University of California Agricultural and Natural Resource folks who run the Statewide Integrated Pest Management Program recommend that dormant spur samples be taken once a year to determine treatment need for the control of red and brown mites and San Jose scale.
“Take your sample early in the year,” they advise. “Randomly select between 30-50 trees from each plot or orchard. Choose 2-3 random spurs from the inside of each tree’s canopy near the main scaffold.”
With a goal of 100 spur samples total, “(c)lip the spur off at the base, making sure to include some old spur wood along with the past season’s growth to detect parasite activities on scales.
“Examine 20 or more of the spurs under a microscope or with a hand lens to note the presence or absence of mite eggs and live parasitized scales. If a large number of scales have been parasitized, minimize the insecticides during the growing season and use those not harmful to naturally-occurring parasite populations.”
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