Applications

Major Nutrient Managements

Boron deficiency

Boron (B) is required in young growing tissue. In Washington and most tree fruit species, B deficiencies are common. Deficiency levels can be determined in the soil and leaves with standard testing. Foliar sprays are effective to manage B deficiency, however keeping soil levels within adequate range is important for root growth. Fertigation can lead to uneven distribution and toxicity (around leaks/junctions) and is not recommended. Boron mobility varies across tissue and development stages; thus, sprays need to be managed during active growth. Relevant application timings are pink to cell division and leaf drop. Excess of boron can lead to severe toxicity and application rate should be calculated carefully. Rates of actual B should not surpass 1.0 lb per acre.

Boron maintenance

Boron (B) is required in young growing tissue. In Washington and most tree fruit species, B deficiencies are common. Deficiency levels can be determined in the soil and leaves with standard testing. Foliar sprays are effective to manage B deficiency, however keeping soil levels within adequate range is important for root growth. Fertigation can lead to uneven distribution and toxicity (around leaks/junctions) and is not recommended. Boron mobility varies across tissue and development stages; thus, sprays need to be managed during active growth. Relevant application timings are pink to cell division and leaf drop. Excess of boron can lead to severe toxicity and application rate should be calculated carefully. Rates of actual B should not surpass 0.5 lbs acre.

Calcium (cracking)

Ca sprays in cherries can reduce the incidence of rain cracking. Effectiveness has been variable, as it depends on multiple environmental factors. Calcium Cloride CaCl has proven the most effective. Concentration and coverage are key factors for improved efficacy. Application timing is pre harvest during and post rain events. Note that post-harvest dipping has proven most effective for cracking (Winkler and Knoche, 2019)

Calcium deficiency

Calcium (Ca) is needed for cell wall development and strengthening, thus essential during fruit cell division stage. In Washington, soil deficiencies are rare, however given the limited mobility of Ca within the plant, fruit deficiencies might still be present. Deficiency levels in the soil and leaf can be determined with standard testing, while fruit deficiency is not well predicted with tissue testing. For Apples and Pears deficiency: Rate of 2-4 lbs of actual Ca per acre per application, from petal fall to late June. Up to 15 lbs of actual Ca per season.

Copper Deficiency

Copper (Cu) deficiencies are rare, given that several pesticides contain Cu. Deficiency levels can be determined in the soil and leaf with standard testing. Symptoms of Cu deficiency include chlorosis, leaf margin necrosis and curling. Given the low mobility of Cu in the plant, frequent applications during the growing season might be needed to overcome deficiencies

Iron deficiency

Iron (Fe) deficiencies are common in calcareous or high pH soils, also in saturated soils with lack of oxygen. Soil or leaf tissue testing are not good indicators of deficiencies, while symptoms of iron chlorosis are very distinct. Given the low mobility of Fe in the plant, frequent applications during the growing season might be needed to overcome deficiencies

Magnesium deficiency

Magnesium deficiencies are rare in Easter Washington soils, however in Western Washington or sandy soils, Mg can be leached and become deficient. Total Mg demand is low compared to other macronutrients; thus soil natural levels might be sufficient. Deficiency levels of Mg can be determined in the soil and leaves with standard testing. Most effective management of Mg is done via ground application, as it has medium mobility in soils and is mobile in plants. Foliar Mg sprays can be effective when deficiencies appear, usually in spur leaves with high crop loads. Best timing is during active fruit growth or when leaf deficiencies appear.

Nitrogen deficiency

Apply only as needed to apples or cherries. Not effective on pear or other stone fruits and can cause injury.

Zinc deficiency

Annual foliar applications are recommended in calcareous or high pH soils. Preferred timing is late dormant (stone fruit), silver-tip (apples and pears), and post-harvest (all tree fruits except for apricot). Zinc sprays should be avoided during the growing season unless deficiency symptoms occur. Zinc sulfates are common but can cause tissue damage when temperatures are greater than 85 ºF after the application. Zinc sulfate is also not compatible with dormant oil or lime sulfur. Zinc chelates are also available and are less likely to cause russet. If little leaf and/or rosette are present, use deficiency rates. The deficiency rates for Zn sulfate or Zn oxysulfate are 14 pounds actual Zn per acre (dormant timing sprays) and 9 pounds actual Zn per acre (postharvest). If sprays are applied during the growing season, use only 2 to 4 lb actual Zn as Zn sulfate or Zn oxysulfate per acre (non-bearing trees only). Because Zn deficiency is so widespread in Washington orchards, WSU recommends that Zn be applied every year in the form of Zn maintenance sprays even if little leaf or rosette are absent.