1996-1997 New England Apple Pest Management Guide


CALCIUM FOLIAR SPRAYS AND POSTHARVEST DIPS

 

Calcium (calcium chloride or calcium nitrate) tree sprays have been shown to increase the calcium content of the fruit, and to reduce fruit problems that are associated with inadequate calcium: bitter pit, scald, breakdown, and rot. Foliar sprays should begin about 3 weeks after petal fall and be repeated at about 2-week intervals until harvest, totaling about 6 or more applications per season.

Technical grade CaCl2 (77 to 80% CaCl2) should be applied at the rate of 2 to 2.7 lbs./100 gals. dilute until mid-July and at the rate of 2.7 to 3.3 lbs./100 gals. dilute after mid-July.

Ca(NO3)2 may be substituted for CaCl2 but must be applied at the rate of 3.2 to 4.3 lbs./100 gals. dilute until mid-July and at the rate of 4.3 to 5.3 lbs./100 gals. dilute after mid-July. We have tested Ca(NO3)2 only on McIntosh, and have experienced no fruit injury; however, there are reports that Ca(NO3)2 causes fruit spotting on Delicious and Golden Delicious. We have measured no increase in leaf nitrogen levels from the recommended dosage of Ca(NO3)2.

If CaCl2 is applied apart from pesticides a non-ionic wetting agent should be added. The wetting agent may reduce the potential for leaf injury and increase uptake. Since most pesticide formulations include wetting agents, none should be needed when CaCl2 and pesticides are combined. Leaf injury may be enhanced by the addition of captan or Guthion to the CaCl2 spray, but most pesticides are compatible with CaCl2.

Injury appears as a burn at the margins of the leaves. We feel that in most cases this injury is associated with inaccurate sprayer calibration, since the injury is not as prominent when dilute applications are used. Concentrations up to 10X have been very effective, but any inaccuracy in calibration can affect the actual application rate dramatically and result in leaf burn. To reduce the risk of injury to the fruit and foliage, Washington State Cooperative Extension recommends applying CaCl2 with at least 100 gallons of spray water per acre. CaCl2 should be mixed in a pail of water and be added last, when the sprayer tank is nearly full, to ensure thorough mixing.

There must be sufficient agitation to maintain thorough mixing during application. Risk of damage is greatest on weak trees and injured foliage. We are aware of no incompatibility of CaCl2 with commonly used pesticides, but formulations and combinations frequently change, so users should be alert to any unusual behavior of materials in spray mixtures. Under cool, moist conditions, use caution when applying foliar calcium as part of a complex tank mix. Slow drying may increase absorption and increase risk of injury.

Do not tank mix CaCl2 with Solubor or Epsom salts. Do not apply CaCl2 at temperatures above 80oF.

 

Table 23 - Calcium Foliar Spray Rates

 

Applications should begin 3 weeks after petal fall and continue at 2-week intervals until harvest.

 

Calcium Source

Rates per 100 gallons dilute

Until mid-July

After mid-July

Calcium Chloride*

2 to 2.7 lbs.

2.7 to 3.3 lbs.

Calcium Nitrate

3.2 to 4.3 lbs.

4.3 to 5.3 lbs.

 

* Add 2/3 oz. vinegar per pound of CaCl2. Use of surfactant in CaCl2 spray may reduce the potential for foliar injury.

 

The initial pH of technical CaCl2 in water is about 10.3, because small amounts of free calcium oxide are present and form calcium hydroxide in the water. This high pH may reduce effectiveness of some pesticides. We therefore recommend adding 2/3 oz. of vinegar (5% acid content) per lb. of CaCl2 to neutralize the alkalinity and bring the spray solution to about pH 6.0. Addition of vinegar does not affect uptake of Ca by the apples. Materials that will buffer the solution to about pH 6.0 may also be used as an alternative to vinegar. Since Ca(NO3)2 does not raise the pH of the spray solution, vinegar is not required.

Soil management, pruning practices, crop load, and other nutrients have an impact on fruit disorders and fruit storability. Consult the New England Apple Production Guide (W.R. Autio, ed., Cooperative Extension of New England states) for more information on these subjects.


 

Table 24 - Calcium materials for use on apples

 

Product name

% elemental Ca

# Ca per gallon or pound

manufacturer

Product amount per acre per spray (min-max)

# Ca per acre per spray (min-max)

CaB

6

0.6

Stoller, Inc.

3-6 pts.

0.22-0.45

CaB'y

10

1.19

Stoller, Inc.

2-4 qrts

0.58-1.19

Calcium chloride (77-80% CaCl2)

27.8

0.28

many

1.8-6.2 lbs.

0.50-1.74

Calcium chloride (35% CaCl2)

12.6

1.42

many

0.35-1.24 gals.

0.50-1.76

Cor-Clear Dry

34.5

0.34

SEGO Intl.

4-8 lbs.

1.36-2.72

Foliar Ca. Folical

10

0.96

Agrimar Corp.

1 gal.

0.96

Fung-Aid

10

1.19

Stoller, Inc.

2-4 qrts.

0.58-1.19

Link Calcium 6%

6

0.62

Wilbur-Ellis Co.

2-4 qrts.

0.31-0.62

Mora-Leaf Ca. (94% CaCl2)

34

0.34

Wilbur-Ellis Co.

4-8 lbs.

1.36-2.72

Nutri-Cal 8% Calcium Solution

8

0.89

CSI Chem. Corp.

1-2 qrts.

0.22-0.44

Nutra-Phos 10

10

0.1

Leffingwell Div.

3-10 lbs.

0.30-1.0

Nutra-Phos 12

11

0.11

Leffingwell Div.

3-10 lbs.

0.33-1.1

Nutra-Phos 24

20

0.2

Leffingwell Div.

3-10 lbs.

0.60-2.0

Nutra-Phos Mg

10

0.1

Leffingwell Div.

3-10 lbs.

0.30-1.0

Nutra-Plus Cal-Gard

6

0.6

Custom Chemicides

1-3 qrts.

0.15-0.45

Pit-Stop Dry Con. Foliar Cal. 32.5%

32.5

0.32

Ag-Chem, Inc.

4-8 lbs.

1.28-2.56

Pit-Stop Foliar Calcium 12%

12

1.35

Ag-Chem, Inc.

1.5 gals.

2.02

Sett

8

0.91

Stoller, Inc.

1 gal.

0.91

Sorba-Spray Cal.

8

0.86

Leffingwell Div.

1-4 qrts.

0.21-0.86

Sorba-Spray CaB

5

0.5

Leffingwell Div.

1-4 qrts.

0.12-0.50

Stopit Ca. Conc.

12

1.28

Shield-Brite Div.

2-4 qts.

0.64-1.28

Tracite Ca. 6%

6

0.6

Helena Chem Co

3-6 pts.

0.22-0.45

Traco Pit-Cal Liquid Calcium

12

1.4

Traylor Chem Co

0.5-2 gals

0.7-2.8.

Wuxal Calcium

10.7

1.42

Aglukon Div.

3-4 pts.

0.53-0.71

 

Table 24 and text below adapted from: 1996-1997 Pennsylvania Tree Fruit Production Guide. R.M. Crassweller, Horticulture Section Coordinator; E.G. Rajotte, Production Guide Coordinator. Names in italics are dry formulations, all others are liquids.

 

 

There are many commercial products containing calcium (Table 24). These include liquid formulations that are convenient to use, eliminating the need to pre-mix flake calcium chloride before it is added to the spray tank. In addition, vinegar nay not be needed to maintain an acidic spray solution with many of these products. Per pound of actual calcium, however, these prepared formulations are no more effective than flake calcium chloride.

 

Determining the Amount of Elemental Calcium in a Commercially Formulated Product

From the label, determine the percentage of elemental calcium in the product.

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 the material you will add to the tank. This gives you the amount of elemental calcium per gallon or pound

Determine the amount of formulated material you will apply per acre per application. Multiply this by the number of applications to get the total amount that you will use per acre for the season.

Multiply the elemental calcium per gallon or pound times the amount used per season to get the total amount of elemental calcium for the season.

Compare this amount with the recommended 4 to 14 lbs. of elemental calcium per acre per season.

The amount of elemental calcium per gallon or pound is also useful for comparing products by the cost per pound of elemental calcium.

 

 POSTHARVEST CALCIUM DIPS

Postharvest dips or drenches of calcium chloride can be used to increase the calcium content of apples and reduce the incidence of storage disorders related to calcium deficiencies.

Materials containing calcium chloride are the only calcium sources that may be used. Calcium chloride at 94% purity or higher may be used, and we recommend its use at no more than 12 lbs./100 gallons of water, since damage to the fruit may occur at higher concentrations. We recommend inclusion of 8 to 10 ozs. of 5% vinegar per 100 gallons to counteract the alkalinity of the calcium chloride solution.

Two commercial sources of calcium chloride in liquid formulation are also labeled for use. "STOPIT" liquid calcium concentrate (Shield-Brite Corp.) (12% calcium) is labeled for use at 1 gallon per 74 gallons of drench water. "Decco Calcium Chloride-EC 405" (12% calcium) is labeled for use at 1 gallon per 79 gallons of drench water. Both of these labelled rates of use provide markedly lower calcium concentrations in the solution than does 12 lbs. of calcium chloride (94%) per 100 gallons. However, their formulations make them easier to use than 94% calcium chloride pellets.

All of these calcium materials may be combined with scald-inhibiting chemicals. No postharvest dip or drench should be used without inclusion of fungicide to control postharvest rotting.

 

On to Chemical Control of Watersprouts and Suckers

 

 


1996-1997 New England Apple Pest Management Guide