Calcium enhances condition of stored d'Anjou pears

By Dr. Tom Raese, Research Plant Physiologist (collaborator), USDA-ARS, Tree Fruit Research Laboratory, Wenatchee, Washington

While there are many research reports about the effects of preharvest calcium sprays on control of alfalfa greening, black end, and cork spot, there is a dearth of information about the effects of calcium sprays on postharvest maladies and fruit disorders of d'Anjou pears coming out of cold storage.

Since the late 1970s, many preharvest calcium spray materials and combinations have been tested on several d'Anjou pear orchards in north central Washington State, primarily to determine the effect on controlling fruit disorders in the orchard. In most trials, the incidence of these fruit disorders was reduced by several-fold with calcium sprays compared to unsprayed control trees.

This research report is from an experimental plot near Cashmere, Washington, where various calcium spray materials were randomly assigned to mature d'Anjou pear trees of uniform size and replicated 5 to 15 times on single-tree units. Calcium chloride (CaCl₂) spray materials were applied five times per season, beginning in late May or early June, and applied at about three-week intervals. Sprays were applied with a handgun until run-off. Due to possible injury to fruit and leaves of d'Anjou pear trees from CaCl₂ spray materials, sprays were not applied when temperatures were above 80°F.

For pears, the rate of CaCl₂ (34% Ca) was 1.5 pounds CaCl₂ per 100 gallons of water versus 3.0 pounds CaCl₂ for apple trees. All data in this report are derived from visual observations and appropriate rating systems.

Fruit skin color on d'Anjou pears out of regular cold storage from trees sprayed with calcium chloride was significantly more green than on unsprayed controls (see Figure 1). This may indicate that CaC1₂-treated fruit stored well and also should have improved shelf life. Fruit from calcium chloride treatment had only minimal CaCl₂ markings on the skin. A rating of three is considered borderline acceptable, and a rating of five is severe CaCl₂ markings (see Figure 1).

Nevertheless, overall appearance and fruit finish was significantly higher on calcium chloride-sprayed fruit (see Figure 2). Juiciness, white flesh color, and texture were also improved on d'Anjou pears from trees that were sprayed with calcium chloride versus the unsprayed controls.

The incidence of various external rots in storage was significantly less on fruit from trees sprayed with calcium chloride than on fruit from unsprayed control trees (see Figure 3). The percentage of cork spot observed in storage was less on d'Anjou receiving the calcium chloride treatment than on fruit from the unsprayed control treatment (see Figure 3).

Although not statistically significant, the incidence of superficial scald and scuffing marks from handling was less on d'Anjou fruit treated with preharvest sprays of calcium chloride than on fruit from the controls (see Figure 4).

Only minimal evidence of fruit shriveling was observed over the years. In 1988, calcium chloride-treated fruit had less shriveling than in the controls (see Figure 5). In 1990, the incidence of internal browning was less on calcium chloride-treated fruit than in control fruit (see Figure 5). It is noteworthy that external browning on fruit in 1990 was significantly correlated with internal browning (r=0.96). Therefore, external browning on d'Anjou fruits could be used to predict internal browning (see Figure 6).

In conclusion, preharvest calcium sprays may improve the condition of d'Anjou pears coming out of cold storage, and shelf life may also be enhanced. Calcium chloride-treated fruit had improved appearance with fewer physiological disorders and various rots, but caution is needed to avoid unacceptable marking of the fruit due to careless preharvest CaCl₂ spray applications. Use recommended procedures outlined in the Washington State University Crop Protection Guide for Tree Fruits in Washington (Spray Guide).

Results of fruit firmness, soluble solids, titratable acids, and calcium concentrations in fruit were described in the December 1997 issue of the Good Fruit Grower issue.

ACKNOWLEDGMENTS

The author gratefully acknowledges the assistance of Dr. S.R. Drake, Fred Valentine, Winter Pear Control Committee of the Northwest Pear Bureau, Washington Tree Fruit Research Commission, and Bitterman and Flick Orchard.

Calcium enhances condition of stored d'Anjou pears

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