Boron Nutrition of Almonds

This project studies the benefits of foliar B sprays applied at different rates and time on yield and quality of almond and walnut nut crops. The project was initiated in 1994 and completed at the end of the 1998 growing season.

Almond research evaluated the effect of B nutrition on flowering, fruit set, and yield following a similar (and very successful) study with pistachio. Spraying B at a rate of 1 to 2 lb Solubor/100 gal on B deficient almond trees significantly increased fruit set and yields in 1995 and 1996. Of special note is the fact that often almond trees responded positively to supplemental B sprays without showing visible B deficiency symptoms. Results in 1997 suggest an optimal application is to mix 3 lb Solubor with compatible insecticides and fungicides to reduce application costs and to spray postharvest.

Walnut research was initiated in 1997. Foliar B treatments dramatically increased walnut set and retention, reduced or totally eliminated pistillate flower abortion (PFA) and increased ultimate nut yield. Results in 1998 were variable across three sites and strongly affected by prevailing weather conditions. At sites where PFA was not as severe, the application of B had no effect on reducing PFA. At a site with the most prevalent PFA of around 58 percent, B sprayed two weeks after nut set reduced PFA by around 16 percent and increased yield by 20 percent.

Boron is fundamentally essential for the flowering process and since 80 percent of all agricultural products develop from the flowering part of plants, the implications of this research are very wide ranging. CA-13F