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Calcium sprays
Sprays of calcium chloride have been successful in reducing or commercially controlling corking and bitter pit, but seldom have these sprays completely eliminated the problem. Extensive research has been conducted around the world to define the products, rates, and timings that will minimize the incidence of low-calcium physiological disorders in apples. The major portion of the research has been conducted on Golden Delicious and York Imperials. However, recommendations developed from research in Pennsylvania have effectively controlled corking and bitter pitting in nearly all varieties.
The effective use of calcium chloride tree sprays may be the most cost-effective, quickest cultural practice for reducing low-calcium physiological disorders in apples. We recommend applying 15 to 50 pounds of calcium chloride per acre per season in six to eight cover sprays. Calcium in the form of calcium chloride is recommended because of its proven effectiveness and lower cost.
Other products that supply calcium are available. Many are recommended at rates that supply lower amounts. These products may be beneficial when only small amounts of calcium are needed to correct the deficiency. To evaluate other materials effectively, growers should compare the cost per pound of actual calcium and the amount of formulation needed to achieve an equivalent rate to the 15 to 50 pounds of calcium chloride per acre per season needed to control problems. See "Determining the amount of elemental calcium in a commercially formulated product." Growers experiencing severe bitter pit on summer cultivars, especially Summer Rambo, may need to apply special calcium sprays in addition to cover sprays.
15-20 pounds per acre per year: This is the lowest rate that should be used. It will give some control of bitter pitting and corking, will cause no leaf burning, and will probably not enhance storage life of the fruit.
20-30 pounds per acre per year: This rate should give good control of preharvest physiological disorders and probably should be the standard rate where these disorders are chronic problems. It will not cause any significant leaf injury and will probably not enhance the storage life of the fruit.
30-40 pounds per acre per year: This rate should give excellent control of corking and bitter pitting and should be the intermediate rate for Pennsylvania. It may somewhat enhance the storage potential of apples and should result in almost no leaf injury.
40-50 pounds per acre per year: This is probably the highest rate that should be used in Pennsylvania and should give outstanding control of corking and bitter pit. This rate may result in some slight burning on the edges of the leaves, but it usually does not appear until mid-September or October. This rate may enhance the storage life of the fruit.
Applying calcium chloride sprays
Time of application: Include in all cover sprays. Do not premix calcium chloride with Solubor in a small volume of water before adding to the tank, when both materials are to be applied together.
Gallons per acre: No restrictions; sprays with as little as 20 gallons per acre have been effective.
Compatibility: At the rates recommended, calcium chloride and/or Solubor may be mixed with spray oil (Superior 70 Sec.), with WP formulations, or with EC formulations of the more common fruit pesticides. Compatibility of materials other than calcium chloride is uncertain, and growers should either check the label for information or conduct a compatibility test in a small jar.
Leaf injury: Some leaf injury may occur from calcium chloride sprays following wet, cool springs or hot, dry summers. When injury is noticed, reduce calcium chloride to one-half the rate in the next spray or delete calcium chloride from the cover sprays until one-half inch of rain has fallen.
Equipment: Calcium chloride can corrode some types of spray equipment. Few problems have occurred if sprayers and tractors are rinsed after use. The newer sprayers made of stainless steel, fiberglass, or various plastics that are rust resistant are desirable.
Special considerations: If early maturing cultivars continue to exhibit bitter pitting and storage breakdown after the standard rate of calcium chloride has been used, a higher rate should be used. Only calcium that hits the skin of the fruit can increase fruit quality. Therefore, in the standard program, 8 pounds of calcium per acre per year may be applied to Delicious, Rome Beauty, and Golden Delicious, but early maturing cultivars such as Summer Rambo may be receiving only 4 pounds of calcium per acre per year prior to harvest.
In summary, many factors influence fruit calcium concentration, and since it is difficult to raise fruit calcium level, growers should use all methods possible to gain the upper hand against corking, bitter pitting, and other low-calcium-related disorders. Cultural practices involve soil and nutritional factors as well as tree vigor and fruit density.
Determining the amount of elemental calcium in a commercially formulated product
1. Look for, or determine, the percentage of elemental calcium in the product. This should be listed somewhere on the label.
2. For a liquid formulation multiply the percentage by the weight of the material per gallon. For a solid multiply the percentage by the weight of material you will add to the tank. Result equals the pounds of calcium per gallon or pound of formulated product.
3. Determine the rate of formulated material you intend to apply per acre per application. For a specific calcium product this is usually listed on the label.
4. Multiply the amount of material per acre by the number of applications to be made during the season. Result equals the amount of total product per acre per season.
5. Multiply the amount of total product per acre per season (from Step 4) by the pounds of calcium per gallon or pound of formulated product (from Step 2). Result equals the total amount of elemental calcium per acre per season.
6. Compare the result from Step 5 with our recommendation of 4 to 14 pounds of elemental calcium per acre per season.
7. Compare the season-long cost of materials. Multiply the amount of material used per season times the cost of the material.
Example 1. Product A sells for $6.50 per gallon and is a liquid listed as containing 15% elemental calcium. The weight per gallon is 12 pounds. The label recommends 2 to 4 quarts per acre per application with eight applications suggested per season. You decide to apply 2 quarts per acre per application.
Step 1: Product contains 15 percent elemental calcium.
Step 2: 12 lb x 0.15 = 1.8 lb of elemental calcium per gal.
Step 3: You choose to apply 2 quarts (or 0.5 gal) per acre per application.
Step 4: 0.5 gal per acre per application x 8 applications per season = 4 gal of material per acre per season.
Step 5: 4 gal x 1.8 = 7.2 lb of elemental calcium per acre per season.
Step 6: Our recommendation is 4.0 to 14.0 lb of elemental calcium per acre per season.
Step 7: 4.0 gal x $6.50 per gal = $26.00.
Example 2. Product B sells for $1.50 per pound and is a solid powder containing 30 percent elemental calcium. The label recommends 3 to 4 pounds per acre per application with eight applications suggested per season.
Step 1: Product contains 30% elemental calcium.
Step 2: 1 lb x 0.30 = 0.30 lb of elemental calcium per lb of material.
Step 3: You choose to apply 3.0 lb of material per acre per application.
Step 4: 3 lb per acre per application x 8 applications per season = 24 lb of material per acre per season.
Step 5: 24 lb x 0.30 = 7.2 lb of elemental calcium per acre per season.
Step 6: Our recommendation is 4.0 to 14.0 lb of elemental calcium per acre per season.
Step 7: 24 lb x $1.50 per lb = $36.00.
Comparing costs
You wish to compare the cost per pound of elemental calcium in two products. From Products A and B above, we can determine which is cheaper.
1. Determine the pounds of elemental calcium per gallon or pound of formulated product for each product you are considering. (Same as in Step 2 above).
2. Determine the cost per pound of elemental calcium in each product.
3. Compare the two materials' cost.
Example: From Products A and B above, determine which is cheaper per pound of elemental calcium.
Step 1:
Product A = 12 lb x 0.15 = 1.8 lb of elemental calcium
Product B = 1 lb x 0.30 = 0.30 lb of elemental calcium
Step 2:
Product A = $6.50 per gallon ÷ 1.8 lb calcium per gal of
material = $3.61 per lb
Product B = $1.50 per lb ÷ 0.30 lb calcium per lb of material = $5.00 per lb
Step 3:
Product A costs $3.61 per lb of elemental calcium
Product B costs $5.00 per lb of elemental calcium
Determining the amount of product needed to apply 14 pounds of elemental calcium
You are comparing two products to determine what rate you need to apply to achieve 14 pounds of elemental calcium per acre per season. Again use the same two materials outlined above and assume that you will be making eight applications during the season.
1. Divide the number of pounds of elemental calcium desired per season by the number of applications. Result is the pounds of elemental calcium needed per acre per application.
2. Divide the amount of elemental calcium per gallon or pound of material by the pounds of elemental calcium needed per acre per application. Result is the gallons or pounds of formulated material needed per acre per spray.
Example
Step 1: 14.0 lb of elemental calcium per acre per season ÷ 8 applications per season = 1.75 lb
Step 2: Product A = 1.75 ÷ 1.8 lb elemental calcium per gal = 0.97 gal per application
Product B = 1.75 ÷ 0.3 lb elemental calcium per lb = 5.83 lb per application
Warning: The maximum labeled rate per application for Product B is 4 pounds per acre per application. Therefore, you are exceeding recommended labeled rates by using Product B to achieve a 14-pound recommended rate.
In summary, to effectively evaluate materials other than calcium chloride, you need to compare the cost per pound of actual calcium with the amount of the formulation needed to achieve the 4 to 14 pounds of actual calcium per acre per season needed to control problems.