A Guide to Successful Bloom Sprays

Bloom sprays are the first opportunity to set the stage for a successful growing season by directly affecting the yield and quality of the crop. By applying the right nutrients, growers can ensure a proper nut and fruit set, increased pollen viability, and improved pollination, and support early-season energy processes.

The Importance of Bloom Spray Nutrition

Yield and quality responses to specific foliar applied nutrients have been well documented by universities for both orchards and vineyards. Bloom and early fruit set are the most critical periods for setting and retaining fruit. Nutrients like zinc, calcium, and boron are critical for pollen tube elongation and ultimately help assure the success of pollination and fertilization. Nutrients like iron, manganese, and zinc are critical for chlorophyll formation and leaf and fruit expansion. They help assure the early season photosynthetic potential of the crop. Flowering parts and emerging leaves are very tender and have less waxy cuticle than fully matured leaves, therefore they absorb foliar applied nutrients more efficiently. All of the previously mentioned nutrients are not highly phloem-mobile. Applying these nutrients directly on the flowers & early leaves requires that the nutrients move only short distances from where they enter the plant.

Boron

Boron is essential for pollen tube elongation and hydration. Boron plays a critical part in the polymerization of cellulose and lignin fibers. Where calcium is the ”cement” between cells, boron is the ”rebar” that strengths it. It is critical for cell elongation and for the strength of cell walls. Studies show that foliar applications of boron before bloom (pink bud in orchards) lead to improved fruit set and yield.

Phosphorus

Phosphorus is vital for photosynthesis, respiration, energy storage and transfer, and cell division. It also supports ATP formation to replenish plants’ energy supply, which is at its lowest point, pre-bloom. Phosron® Foliar has been proven to optimize cell division, cell orientation, and cell differentiation, thus producing a strong pollination, fruit and nut set, and eventual yield.

Calcium

Calcium is essential for pollen tube development and strength and has a direct role in the fertilization process. For many tree crops, especially pome fruits and stone fruits, foliar applied calcium sprays have been shown to improve fruit quality. Calcium is a critical part of calcium pectate, the ‘‘cement” that strengthens and cements cell walls, however, it is not very mobile in the plant. Studies show that calcium applications are most effective during the entire period of cell division and cell elongation. For example, multiple applications of calcium have been required on apples to reduce bitter pit and improve storage life. Studies by researchers in Michigan show that FBSciences’ nutrient products, formulated with FBSciences’ proprietary biostimulant technology FBS Transit®, are more effective than other foliar nutrient products at increasing fruit set, average weight per fruit, and quality of fruit (see chart below).

The physiology of pollination and bloom set is driven by 5 key nutrients; P, Zn, Ca, B and Mo. Application of these nutrients helps to optimize a uniform pollination and early fruit and nut set. This early uniformity leads to a more uniform bulking and maturity. The above apple trial in Michigan improved fruit set by 7.1% and statistically improved yield per tree by 25.2%.

Zinc

Every protein needed for bloom is a zinc-dependent protein, thus zinc is essential for bloom. Not only is zinc essential for proper cell elongation, it is also deficient in many western soils. Post-bloom applications help to enhance chlorophyll density and full leaf expansion. In vineyards, zinc is also important for the full expansion of fruit bunches. University of California research has shown favorable yield responses to post-bloom applications of zinc. Research has shown Zicron® Foliar to have superior nutrient uptake and internal movement within the plant than less advanced zinc formulations. Studies by UC Davis showed that Zicron® Foliar was the top-rated commercial zinc product in terms of foliar uptake efficiency (see chart below).

Research conducted at UC Davis. Zicron Foliar was previously named Zicron-F.

Iron & Manganese

Many western orchards exhibit symptoms of iron and manganese chlorosis during spring and summer months. Normally the iron and manganese deficiencies are due to soil pH, free lime, or high bicarbonate irrigation water. Carbonates and bicarbonates tie-up these nutrients in the soil and make them less functional in the plants. Frequent foliar applications of iron and manganese may be required in order to assure normal chlorophyll formation and reduce symptoms of chlorosis.

Molybdenum

Molybdenum has a complementary role with boron in the pollination of a wide variety of crops. Studies suggest that when moly is applied with boron, pollen germination is increased at a higher rate than when boron is applied alone. Moly also plays a vital role in nitrogen metabolism, which has bloom retention benefits when the first leaf flush can utilize nitrogen easily and become photosynthetically active sooner.

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