WSU-TFREC

NUTRIENT SPRAYS

contributed by Dr. Frank Peryea & Dr. Kathleen Willemsen
WSU-Tree Fruit Research & Extension Center

Fertilizers can be applied to fruit trees as nutrient sprays. Although only limited amounts of nutrients can be absorbed by the tree through foliar application methods, such spray applications can be timed for maximum effect in overcoming or preventing certain mineral deficiencies or to enhance tree performance and fruit quality.

Caution: Nutrient sprays can cause severe injury to fruit, leaves, shoots and buds. Therefore their use should be considered as hazardous. Do NOT apply unless a deficiency or low level of that specific nutrient is known to exist and has been confirmed by visual symptoms or tissue tests. Use dilute sprays and as low a rate as possible. Concentrates can cause serious injury.

Note: Nutrients are not classified as pesticides and therefore do not require pesticide label registration. Only a limited number of materials are specifically formulated and labeled for use as nutrient sprays. Do not combine these with pesticides unless permitted on the product label. Use of products not labeled for nutrient sprays may result in crop injury.

Information on specific nutrients: Detailed text and explanation of recommendations

Boron Calcium Copper Iron Magnesium Urea (N) Zinc

Boron: Boron deficiencies are common in fruit trees throughout  the Pacific Northwest. Dry soils, particularly in the fall, aggrevate the problem. Symptoms include poorly developed stamens in the blossom, blast of pear blossoms, inadequate fruit set, low seed numbers, bark necrosis in apple, fruit cork, and sometimes fruit cracking.

Deficiencies in most orchards can be prevented or corrected by soil applications of boron, broadcast over the entire soil surface. One application should last up to three years. Because of the potential for serious injury and even loss of the crop or trees if too much boron is used, precautions should be taken. Do not apply more than 3 pounds of actual boron per acre unless higher rates are required as determined by soil tests, sampling to 3 feet. If an aircraft is used for soil application, apply only during the dormant season.

Spray applications can be used to prevent the development of deficiency symptoms or to correct deficiencies. An annual application at a low maintenance rate should supply sufficient boron to prevent deficiencies. This may be applied at any time but is more effective in improving blossom quality and fruit set if applied shortly before full bloom . Sprays can also be applied early during the growing season or postharvest while the leaves are still green and active. Higher maintenance rates may be required for orchards planted on very sandy or calcareous soils or in the White Salmon area. Use the annual per acre deficiency rate at these locations, applying half the boron in a single pre-bloom spray and the remainder in one or more postbloom sprays. Boric acid and polyborate-based spray products are equally effective when applied as single-product sprays.  With the exception of Mor-Bor 17, all boron spray products tested to date at WSU produce alkaline spray tank solutions and may require acidifying adjuvants if used in pH-sensitive tank mixes.  Tank mixes with Mor-Bor 17 may require acidification when prepared using alkaline well water.  Because boron product and water chemistries vary, the best practice is to measure and adjust the pH of the boron product-water-acidifier mix before adding pH-sensitive pesticides or growth regulators.
Table for prepink/pink applications

If deficiencies appear during the growing season, apply boron as soon as possible but do not use higher rates after May because of the potential for fruit breakdown in storage. If deficiency symptoms occur frequently, make soil tests and consider ground applications.
Table for foliar applications after bloom

Where pear "blossom blast" occurs, make spray applications in the fall after harvest while the leaves are still green and active or in the spring during the first to full white blossom stages. Note: blossom blast is readily confused with false fireblight (Pseudomonas blight) and fireblight. See section on Diseases of Apples and Pears.
Table for postharvest applications

Caution: Both high rates and high concentrations of boron can cause shoot dieback and even tree death. High rates or late applications during the growing season can cause severe fruit loss in storage.

Calcium: Calcium sprays applied to fruit during the growing season may reduce the incidence of certain fruit disorders and may improve fruit quality. Responses to calcium sprays are not predictable from calcium levels in soil or leaves. Physiological disorders such as bitter pit of apples, cork spot and alfalfa greening of Anjou pears, and cracking and firmness of cherries are often related to calcium content of the fruit. However, the relationships are not precise.

The most commonly used calcium spray material is calcium chloride, available as either food-grade product or specifically formulated for use as a foliar spray. Construction-grade calcium chloride contains impurities that can severely damage fruit. Calcium chloride can cause leaf burn and fruit injury, and has limited compatibility with pesticides (see sections on Plant Injury-Chemical Combinations and Limited Compatibility Materials). Calcium nitrate has also been successfully used to reduce bitter pit of apple; however, it is more likely to cause fruit injury than calcium chloride. Calcium nitrate sprays applied at the rates and frequencies for bitter pit control will not improve green color of green apple varieties and may produce a duller red color in red apple varieties. The practice of using calcium nitrate during the first half of the season then switching to calcium chloride for the latter half has not been tested in Washington but has theoretical merit. Foliar sprays of calcium sulfate may actually increase bitter pit and should not be used. Calcium-containing chelates and organic complexes have not been found to be more effective than calcium chloride. Use only chelates and organic complexes that are specifically labeled for foliar application to tree fruits.

Table for foliar applications of calcium during the growing season.

Caution: The risk of calcium chloride or calcium nitrate causing fruit russett increases with increasing number of applications, high rates, and when applied at less than 100 gallons per acre. The possibility of injury is highest at gallonages where droplets coalesce and pool on the lower part of the fruit. The hazard is reduced by using low rates and dilute sprays. Avoid spraying calcium chloride or calcium nitrate under slow drying conditions or at temperatures above 80 to 85F. Fruit size of cherries may be reduced by calcium chloride sprays.

Bitter pit of apple is a physiological disorder often related to low fruit calcium levels. Five to eight applications of calcium chloride or calcium nitrate applied at periodic intervals from early June through late August will significantly reduce the risk of bitter pit development. Effectiveness varies with variety, orchard location and growing season. If severe bitter pit is common, more frequent applications may be required. Calcium sprays are not required in orchards that historically have not produced fruit with bitter pit.

Cork spot and alfalfa greening of Anjou pears are physiological disorders which are often reduced by foliar calcium chloride sprays. Pears are more susceptible to calcium injury than are apples. Foliar sprays of calcium nitrate should not be used on pears. Apply no more than 4 pounds calcium chloride dissolved in 400 to 800 gallons per acre (the 800 gallon rate is for larger trees). Make four to five applications at 3-week intervals from June to August.

Fruit firmness and rain cracking of cherries are influenced by calcium chloride sprays. Research suggests that three or more sprays applied at weekly intervals before anticipated harvest are likely to reduce fruit softening, postharvest injury and minor rain cracking. Severe cracking will not be prevented. Fruit size may be reduced.

Copper: Copper deficiency or "wither tip" has become more common in Washington apple and pear orchards. About mid-June, terminal leaves on part or most of the tree turn yellow, wither and fall. Bark may be cracked and rough.

Postharvest foliar applications of 1 pound of copper per acre as copper sulfate or basic copper sulfate will usually correct the symptoms. If symptoms are severe, mid-season sprays of copper chelate or basic copper sulfate products (bearing trees) or copper chelate, copper sulfate, or basic copper sulfate products (non-bearing trees) can be applied but may cause foliage and fruit injury.
Table for postharvest applications of copper
Table for foliar applications of copper during the growing season

Adding copper to zinc dormant sprays will not increase tree copper levels.

Caution: All copper products are potentially phytotoxic. Applying copper sprays when fruit is present can cause severe fruit russetting, particularly on Anjou. If possible, delay applications until after fruit harvest. Fruit injury can sometimes occuir when foliar copper products are mixed with calcium chloride or applied within a week of calcium chloride sprays. Excessive copper application can increase soil copper to levels that are toxic to fruit trees.

Iron: Trees affected by iron chlorosis may be made green by foliar applications of iron chelates or similar compounds. This is a temporary measure and does not correct the basic cause. Usually two sprays are required. Apply the first about 4 weeks after bloom and the second about 3 weeks later. Apply as a separate spray.
Table for foliar applications of iron during the growing season

Caution: Some iron chelate sprays may cause severe injury to fruit, especially pears.

Magnesium: Chronic magnesium deficiency is best treated with soil applications of magnesium fertilizers or dolomite. Apply magnesium sprays only when moderate or severe deficiency symptoms appear suddenly or are not controlled by soil applications of magnesium. To avoid creating other nutrient imbalances, magnesium deficiency should be confirmed before applying sprays. Two sprays are required. Apply the first spray during June and the second about 4 or 5 weeks later. Apply as a separate spray. Trees with little or no fruit need not be sprayed as the deficiency is severe only on trees with heavy crops of fruit.
Table for foliar applications of magnesium during the growing season

Urea: Urea sprays may be used on apple trees to supplement soil applications of nitrogen. They are not effective on stone fruits or pear and can cause injury.

To reduce the hazard of injury on apples do not use rates over 3 to 5 pounds of urea per 100 gallons of water, or more than 10 to 20 pounds per acre.
Table for foliar applications of urea during the growing season

Caution: On apple use only formulations that contain less than 2% biuret because of potential injury. Applications of urea with some pesticides can reduce their effectiveness. On the other hand, applications with growth regulators can increase their absorption, resulting in an overeffect.

Zinc: Low levels of zinc and deficiency symptoms are common in eastern Washington. The visual symptom is small, thin leaves. With acute deficiencies, leaves also appear chlorotic (pale yellow) and new growth is limited to a short rosette. The first symptoms of a deficiency with spur-type Red Delicious apples may be a limited number of small leaves on spurs, poor fruit set and small fruit size.

Soil applications of zinc have not been effective except with young trees where applications have been worked into the soil prior to tree planting. Effects can last for 3 to 5 years. Spray applications of zinc are required with established trees. Annual applications are more effective in preventing deficiencies than making applications at high rates every 2 or 3 years. Ground sprayer applications are more effective than those by aircraft because they give a better distribution of zinc to the lower and inside portions of trees where weak spurs, lower levels of zinc and small fruit size are greater problems.

Where zinc levels are known to be low, make annual spray applications at low rates, either after harvest in the fall while leaves are still green and active, or as a dormant spray in the spring. Higher rates of zinc can be applied in the early spring than in the fall. With an acute deficiency, both a fall and spring application may be necessary.

Where zinc deficiency symptoms are observed during the growing season, avoid the use of zinc sulfate because of potential injury to fruit and foliage. Various zinc chelates and organic complexes are available which reduce the potential for injury. They differ in their compatibility with oil, and in their effectiveness, particularly in correcting deficiencies. Follow manufacturer's directions carefully.

Caution : Excess zinc and high rates of application can cause severe injury to shoots, buds, leaves and fruits. When using zinc sulfate crystals be certain all crystals are dissolved before spraying or injury can occur. Zinc sulfate is highly corrosive. After use, thoroughly rinse spray tank, pump, lines and nozzles.

Zinc Dormant Spray Application. The most effective time to apply zinc is in the spring before the buds open. Higher rates can be used at this stage than later in the season. To improve effectiveness and reduce potential injury, delay spray applications as late as possible, but spray at or before stage 2.
Table for dormant applications of zinc

Caution: Injury from spring applications has been associated with oil sprays and cool weather at the time of application. Some zinc formulations can be applied with oil as shown on the label. It is suggested that zinc sulfate and other formulations not be applied within three days before or after applying oil. Longer periods may be desired during cool weather. Where multiple applications of oil are required on pear, or where management problems occur, late fall applications of zinc are suggested.

Zinc Foliage Applications. Where deficiency symptoms occur during the growing season, spray applications should be made. If symptoms occur late in the season and fruit is present, delay applications until after harvest. To aid absorption, thoroughly wet foliage.
Table for foliar applications of zinc during the growing season

Caution: Where fruit is present, applications to apple and pear can cause fruit russeting. This is most likely to occur under cool, slow drying conditions in the spring. On bearing stone fruits, use lower rates or organic complexes.

Zinc Postharvest Applications. Zinc may be applied in the fall, but fall applications are usually less effective than those made in spring as a dormant application. Fall application may be needed where deficiencies are difficult to correct or where multiple applications of oil in the spring may cause injury. With some deficiencies, particularly on sweet cherry, both a fall and spring application may be necessary.

Make applications after harvest while leaves remain green and active, but before the trees have begun to go dormant.
Table for postharvest applications of zinc

Caution: High rates of zinc sulfate create potential for injury, particularly to buds. Late-maturing varieties are more susceptible to such injury. Postharvest applications of zinc sulfate, especially concentrate sprays, frequently cause direct injury to leaves and possible buds. Zinc chelates are less likely to cause direct injury. Do not make fall zinc applications to apricots.


Spray Guide recommendations:

Dormant and Delayed Dormant Prepink or Pink (Apple)
First white/full white (Pear)
Foliar--After bloom and before harvest Postharvest--Apply after harvest and while leaves are still green and active.

Program for Nutrients Table

Nutrient Alternate materials or combinations Amount per acre Amount per 100 gallons (dilute sprays) Remarks and restrictions
DORMANT AND DELAYED DORMANT
Zinc maintenance 1. zinc sulfate, dry, 36% Zn 6-12 pounds 1.5-3 pounds Dormant spray only. Dissolve in hot water before adding to spray tank. See precautions in text.
2. basic zinc sulfate, dry, 50-52% Zn 6-12 pounds 2 pounds (with oil) Oil-free sprays are more effective. Follow manufacturer's recommendations for oil sprays.
3 pounds (w/o oil)
3. basic zinc sulfate, liquid, 20-25%Zn   Follow manufacturer's label for rates.
4. zinc sulfate, liquid, 10-12% Zn 2-4 gallons 0.5-1.0 pounds Dormant spray only.  See precautions in text.
5. zinc chelate or organic complex   Follow manufacturer's label for rates.
Zinc deficiency 1. zinc sulfate, dry, 36% Zn 40 pounds 10 pounds Dormant spray only. Dissolve in hot water before adding to spray tank. See precautions in text.
2. basic zinc sulfate, dry, 50-52% Zn 16 pounds 4 pounds Apply without oil.
3. basic zinc sulfate, liquid, 20-25%Zn   Follow manufacturer's label for rates.
4.  zinc sulfate, liquid, 10-12% Zn 12 gallons 3 gallons Dormant spray only.  See precautions in text.
5. zinc chelate or organic complex   Follow manufacturer's label for rates.
PREPINK OR PINK
Boron maintenance 1. sodium borate, dry, 16.5-20.5%B 2.5-3 pounds 0.75 pound All products - Apply amount equivalent to 0.5 lb actual B per acre. See text.
2. boric acid liquid, 10%B 2 quarts 1 pint
3. boric acid liquid, 2.5% B 2.25 gallons 2 quarts
4. boric acid, dry, 17% B 3 pounds 0.75 pounds
Boron deficiency 1. sodium borate, dry, 16.5-20.5%B 5-6 pounds 1.25-1.5 pounds All products - Apply amount equivalent to 1.0 lb actual B per acre. See text.
2. boric acid liquid, 10%B 1 gallon 1 quart
3. boric acid liquid, 2.5% B 4.5 gallons 1.25 gallons
4. boric acid, dry, 17% B 6 pounds 1.5 pounds
FOLIAGE - After bloom and before harvest
Boron maintenance 1. sodium borate, dry, 16.5-20.5%B 2.5-3 pounds 0.75 pound All products - Prepink to pink or postharvest timing is preferred. Apply amount equivalent to 0.5 lb actual B per acre. See text.
2. boric acid liquid, 10%B 2 quarts 1 pint
3. boric acid liquid, 2.5%B 2.25 gallons 2 quarts
4. boric acid, dry, 17% B 3 pounds 0.75 pounds
Boron deficiency 1. sodium borate, dry, 16.5-20.5%B 5-6 pounds 1.25-1.5 pounds All products - Apply only if boron deficiency appears during growing season. Apply amount equivalent to 1.0 lb actual B per acre. See text.
2. boric acid liquid, 10%B 1 gallon 1 quart
3. boric acid liquid, 2.5%B 4.5 gallons 1.25 gallons
4. boric acid, dry, 17% B 6 pounds 1.5 pounds
 
Calcium (cherry fruit firmness and reduced cracking) 1. calcium chloride, dry, 34-36%Ca 8-12 pounds 2-3 pounds Limited effect and can reduce fruit size. Three or more applications are needed at weekly intervals before anticipated harvest. See text.
2. calcium chloride liquid, 12%Ca 4 quarts 1 quart
Calcium (bitterpit of apple) 1. calcium chloride, dry, 34-36%Ca 6-8 pounds 1.5-2 pounds All products - Apply five to eight applications from early June to late August. Dilute sprays are most effective. Can cause fruit injury. See text.
2. calcium chloride liquid, 12%Ca 4 quarts 1 quart
3. calcium nitrate liquid, 6-11%Ca 4 quarts 1 quart
Calcium (alfalfa greening of pear; cork spot of Anjou pear) 1. calcium chloride, dry, 34-36%Ca 6-8 pounds 1.5-2 pounds Both products - Apply four applications from early June to August. Dilute sprays are most effective. Can cause fruit injury. See text.
2. calcium chloride liquid, 12%Ca 4 quarts 1 quart
 
Copper deficiency 1. copper chelate or organic complex Both products - Follow manufacturer's label.
2. basic copper sulfate, liquid May be incompatible with calcium chloride. Can cause fruit injury. See text.
 
Iron (lime-induced chlorosis) 1. iron chelate or organic complex   Follow manufacturer's label.
 
Magnesium deficiency 1. magnesium nitrate, dry, 13.5%Mg 20-40 pounds 5-10 pounds Apply in June. Repeat in July if necessary. Do not apply after August 1. Follow manufacturer's label for labeled product rates. See text.
2. magnesium nitrate 0.4LC 6-12 gallons 1.5-3 gallons
3. calcium nitrate (fertilizer grade)
+ Epsom salts (magnesium sulfate)
24-48 pounds 6-12 pounds
40-80 pounds 10-20 pounds
4. magnesium chelate or organic complex  
 
Nitrogen deficiency 1. urea 2-10 pounds 0.5-2.5 pounds Apply only as needed to apples. Not effective on pear or stone fruits and can cause injury. See text.
 
Zinc deficiency, nonbearing trees 1. zinc sulfate, dry, 36% Zn 6-12 pounds 1.5-3 pounds All products - see precautions in text. Can cause injury, particularly on stone fruits. Follow manufacturer's label for labeled products.
2. basic zinc sulfate, dry, 50-52% Zn 6-12 pounds 1.5-3 pounds
3. basic zinc sulfate, liquid, 20-25%Zn  
4.  zinc sulfate, liquid, 10-12% Zn 2-4 gallons 0.5-1.0 gallons
5. zinc chelate or organic complex  
Zinc deficiency, bearing trees 1. zinc chelate or organic complex   Follow manufacturer's label.
POSTHARVEST - Apply after harvest and while leaves are still green and active
Boron maintenance 1. sodium borate, dry, 16.5-20.5%B 2.5-3 pounds 0.75 pound All products - Apply amount equivalent to 0.5 lb actual B per acre. See text.
2. boric acid liquid, 10%B 2 quarts 1 pint
3. boric acid liquid, 2.5%B 2.25 gallons 2 quarts
4. boric acid, dry, 17% B 3 pounds 0.75 pounds
Boron deficiency 1. sodium borate, dry, 16.5-20.5%B 5-6 pounds 1.25-1.5 pounds All products - Apply amount equivalent to 1.0 lb actual B per acre. See text.
2. boric acid liquid, 10%B 1 gallon 1 quart
3. boric acid liquid, 2.5%B 4.5 gallons 1.0 gallons
4. boric acid, dry, 17% B 6 pounds 1.5 pounds
 
Zinc maintenance 1. zinc sulfate, dry, 36%Zn 6-12 pounds 1.5-3 pounds All products - Do not apply before October 1. Do not apply on apricot. Follow manufacturer's label for labeled product rates.
2. basic zinc sulfate, dry, 50-52% Zn 6-12 pounds 1.5-3 pounds
3. basic zinc sulfate, liquid, 20-25%Zn  
4. zinc sulfate, liquid, 10-12% Zn 2-4 gallons 0.5-1.0 gallons
5. zinc chelate or organic complex  
Zinc deficiency 1. zinc sulfate, dry, 36% Zn 24 pounds 6 pounds All products - Do not apply before October 1. Do not apply on apricot. Follow manufacturer's label for labeled product rates.
2. basic zinc sulfate, dry, 50-52% Zn 16 pounds 4 pounds
3. basic zinc sulfate, liquid, 20-25%Zn  
4. zinc sulfate, liquid, 10-12%Zn 7 gallons 1.75 gallons
5. zinc chelate or organic complex  
 
Copper deficiency 1. copper sulfate, dry, 25%Cu 4 pounds 1 pound Both products - OK to tank-mix with postharvest zinc sulfate or basic zinc sulfate sprays. Follow manufacturer's label for labeled product rates.
2. copper sulfate or basic copper sulfate,liquid, 4-14%Cu  
Nutrient Alternate materials or combinations Amount per acre Amount per 100 gallons (dilute sprays) Remarks and restrictions

Washington State University
Tree Fruit Research and Extension Center
1100 N. Western Ave.
Wenatchee WA 98801

phone: 509-663-8181
fax: 509-662-8714


Copyright © Washington State University Disclaimer
WSU Electronic Publishing and Appropriate Use Policy

Comments concerning this page to webservant@tfrec.wsu.edu (Jerry Tangren)

May 2, 2000