IN YOUR ORCHARD
cation exchange sites into the soil solution where it can be leached from the root zone. With all the challenges of the 2021 season, maintaining irrigation systems may not have gotten much attention. Fall is a good time for irrigation system maintenance. See “Maintaining Microirrigation Systems” UC ANR publication no. 21637, for information on drip and micro-sprinkler system maintenance. It is available online ($20) from anrcatalog. ucanr.edu or your local UCCE office.
buds in time to make a different in set next February.
The general recommendation is for 0.4 lb actual boron/ acre (for example 2 lb/acre of a 20% B material such as Solubor ® ) if hull levels are under 120 ppm boron. Dr. Patrick Brown (UC Davis) believes there may be a benefit to using lower rates of foliar boron (for example, 0.2 lb actual B/acre = 1 lb Solubor ® /acre) if hull levels are between 120-200 ppm B. Hull B levels of 300 ppm B or greater indicate toxic levels of B in the orchard and no additional B is advised. Fall or early bloom (‘pink’ timing) B sprays are equally effective in increasing nut set. However, under drought conditions, I prefer the fall timing. Bloom sprays are applied to protect flowers from disease infection. Research shows that ‘pink’ timing of foliar B improves set, while spraying later in bloom when more flowers are open can reduce set. But, in a dry bloom, the ‘pink’ spray can be skipped to save an application (and fungicide costs) and so the best boron application timing may be missed and possibly applied at a time that could harm set. Fall is also a good time for foliar zinc (Zn) spray, particularly if no Zn was applied the previous season. Higher rates of zinc (for example, 20 lbs/acre zinc sulfate) in late October or early November gets zinc into the trees and can defoliate trees and so helps with foliar disease management. In my experience, a high rate of zinc sulfate doesn’t accelerate defoliation in dry fall weather, but a little rain ahead of the spray helps increase relative humidity and improves defoliation. If the goal is to get zinc into trees while maintaining a healthy leaf canopy to support carbohydrate storage for next bloom, a lower rate of zinc (for example, 5 lb/acre zinc sulfate) in October is an option. Sodium borate (Solubor ® -type materials) and zinc sulfate can be tank-mixed, but keep the solution pH below 6 with an organic acid material (Trifol ® , MixWell™, etc.) to avoid a low grade incompatibility (light brown haze to the spray mix) and reduced boron response. What about nitrogen (N) fertilizer in the fall ? Unless the orchard showed low to deficient N levels in the July leaf sample, fall N application may not be needed. In 3 years
Spraying Boron and Zinc, November scene. Photo: Franz Niederholzer.
Nutrition is an important consideration in the fall, although the focus shifts from macro-nutrients (nitrogen, potassium and phosphorus) to micro-nutrients such as boron (B) and/or zinc (Zn) as adequate levels of these essential elements are critical to bud break timing and function. In the fall, the effective method of B and Zn delivery is a foliar spray. Fall timing of soil B application did not increase flower B levels the next year in several years of research in almonds. Where needed, fall foliar B can significantly increase nut set next year and so deliver the best return on investment of any fertilizer. The goal of fall B spraying is to increase flower B levels and nut set. Soil applied B in the fall will not get to the
4 6
A L M O N D F A C T S
Made with FlippingBook - Online Brochure Maker