This year’s record-breaking almond harvest is the result of carefully planned and executed orchard management programs by California’s almond growers. While the harvest season is one to celebrate, postharvest season is the time to get back to work and prepare for next year’s crop.
Here are some postharvest considerations that will keep almond orchards on track for another record crop in 2009.
Combining zinc and boron
Adequate boron (B) nutrition is required for good almond nut set and crop yield. Boron applied between harvest and leaf fall to trees with plenty of healthy leaves, or with pink-bud fungicide sprays, has been shown to increase flower boron levels. However, adding B at pink bud for one variety may result in reduced nut set in other varieties within the same orchard that may be in full bloom at the time.
A possible alternative is to combine a boron material with zinc sulfate applications that are made in the late fall as a foliar fertilizer and to accelerate leaf drop.
To test the feasibility of this spray combination, a study supported by the Almond Board of California (ABC) and conducted by Franz Niederholzer, farm advisor for Sutter and Yuba counties, evaluated the effect on flower boron concentrations of different combinations of zinc sulfate (36 percent) and polyborate, a source of B sold as Solubor, with and without a buffer, applied in late October of the previous year.
He found these sprays beneficial and tank-mixing with a buffer gave the best results. Specifically, Butte trees on Marianna 2624 (83 ppm B hull levels) were sprayed on Oct. 27, 2006, at the rate of 2 pounds Solubor + 20 pounds zinc sulfate per acre with or without 1 quart Trifol buffer per acre in a spray volume equivalent to 100 gallons per acre.
Without the buffer, the solution did not pass the jar test; however, the addition of the buffer cleared virtually all of the tan haze that formed in the spray solution when the zinc sulfate and Solubor were mixed. Including a buffer significantly increased flower B at the 2007 bloom. Average flower boron concentrations were: untreated 31 ppm; treated no buffer 34 ppm; and treated with buffer 36 ppm. Furthermore, as the data indicate, even with the rapid leaf loss, there was sufficient uptake of boron: the flower B levels were increased over untreated, and the increase was identical to trees that were sprayed with the same rate of Solubor without zinc.
These results indicate that B can be successfully piggybacked with zinc sulfate sprays applied late in the fall. However, to maximize bloom B levels from the combination of zinc sulfate and Solubor in a late fall spray, tank-mixing a buffer should be considered.
Numerous studies supported by the ABC over several years have resulted in a deeper knowledge of the effects of water stress on almond trees, and how this can be managed during periods of drought to make the highest and best use of limited water supplies. This research is summarized at a Web portal for drought water management (http://UCManageDrought.ucdavis.edu) created by UC researchers, farm advisors, and Extension specialists.
Among the research results is the finding by several UC irrigation specialists that moderate stress during the postharvest period will have little effect on subsequent years’ nut numbers, but severe water stress during bud differentiation dramatically reduces fruit set the following spring. The level of stress that trees experience post-harvest is substantially dependent on preharvest irrigation status. Trees going into post-harvest well-watered (or minimally stressed) should be able to tolerate moderate postharvest stress with no ill effects. Short water deliveries were a critical issue for many this year, and growers should take care not to overstress trees that were already stressed by deficits during pre-harvest stages.
If replanting is in your orchard management plan for next year, consider moving your schedule up to this year, in light of the uncertain regulatory climate for soil fumigations. Because of the cost and limitations of fumigation, growers may want to make a careful assessment of which soilborne pests require management and which fumigants will be the most effective, keeping in mind the changing regulations for soil fumigants.
“Coping with More Stringent Soil Fumigant Regulations” is a “Hot Topic” at this year’s Almond Industry Conference, Dec. 10-11 in Modesto. An array of speakers will report on ABC-supported research on fumigation best management practices in light of more restrictions.
On the regulatory horizon are label changes which take into account the bystander protection measures that EPA plans to put into place in 2010. EPA is accepting written public comment related to the implementation of the new regulations until Oct. 30.