By Dr. Thomas T. Yamashita

In years when the winter has been consistently cold, and not interspersed with either warm afternoons or prolonged periods of unseasonably warm weather, such a scenario points to a spring in which crops will break dormancy in an efficient manner. This means that when warm spring weather commences, many deciduous crops will initiate a coordinated growth push in unison, or with minimal intervals between different varieties. In this article, we will review two serious considerations and the appropriate actions to take for deciduous fruit trees in Southern, Central and Northern California: the spring root flush, and the narrow spring pollination window.

Spring Root Flush

For most deciduous trees in southerly areas as Delano and Bakersfield, this physiological event will begin sooner, initiating later in Northern and California. The spring root flush represents one of the most important growth pushes, both for the season as well as the long-term health of the trees. These newly formed roots are the first absorptive tissues to begin mining the soil of both moisture and minerals. Over the many years of studying physiological and pathological soil-borne maladies, I have observed that the occurrence of natural attrition in newly formed roots is typically the first stumbling block for developing plants.

When roots push forward in the spring, the soil temperatures may still be hovering around 45 to 50 degrees Fahrenheit. Such cool soil temperatures can exacerbate the tie-up of key minerals such as phosphorus, potassium, calcium, magnesium and various minor elements. Roots will be able to mine nitrogen efficiently, and thus continue to grow. However, the lagging behind of such nutrients as calcium, phosphorus, and minors contributes to root tissue formation of low integrity.

Thus, several weeks following a typical spring root flush, these roots begin to develop tan or brown zones of attrition, or necrotic lesions. These areas of attrition and necrosis become ideal targets for such soil-borne pathogens as Pythium spp., Phytophthora spp., Fusarium spp., Rhizoctonia spp., and other opportunistic organisms. The significance of this root loss is magnified several-fold, as this represents a loss of absorptive surface area for moisture and minerals, as well as the nullification of an important center for the production and translocation of cytokinin hormones in the root tips.

Consequently, the retained viability of spring roots can set the stage for a successful season, while their loss and attrition will stifle the true potential of the trees. Our research over the years indicates that selective balancing of soil chemistry, as well as the microbial population and its activity levels can positively impact these factors which are critical to root health.

A complete analysis, which we offer through our partner Sunburst Plant Disease Clinic, characterizes soil chemistry, soil biology and soil pathogen pressures to produce a field-specific program of remediation. An integral aspect of these programs is the inclusion of microbial and chemical activation systems developed and sold by Fusion 360.

The Pollination Window

From the inception of flower opening, most plant species have 72 to 96 hours of viable receptivity to effective pollination. An added consideration is the anticipated uniform blossom push.

During this time, Mother Nature seems to make it a point to introduce cool, wet weather. Our research on the intricacies of the pollination process indicates that a limiting factor for achieving effective fertilization is the rate and quality of pollen tube growth. The cool, wet weather typical of this time period provides suboptimal conditions which detract from pollen tube growth within that narrow viability window.

Thus, among other factors, increasing the rate and quality of pollen tube growth in the wake of suboptimal weather patterns can mean the difference between setting a superior crop, or not. Such an effect may be secured with our Fusion 360 Foliar PG-31 nutrient treatment. In both third party and university research, we have observed an up to 85 percent increase in bud set.