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Tuesday, October 10, 2017

Fixing Brown Spots in Pear Flesh

Q. I have a Bartlett pear tree producing fruit with brown spots in the flesh. I understand this is because of a calcium deficiency and is remedied with calcium sprays to the tree. If I put calcium in the soil and let it soak in over the winter months, will this remedy this problem instead of spraying?
The dimples in the outer skin of this pear indicates that the flesh under the skin will have a brown spot in it. This calcium deficiency is called 'corky spot' in pears, "bitter pit" in apples. It can happen in soils full of calcium like many desert soils.
Here the outer skin of the pear is folded back revealing the brown spot in the flesh. It wou't hurt you but it makes the fruit hard to market.
A. No. There is plenty of calcium in our desert soils. That won’t solve the problem. This abundance of calcium is locked up by the soil and not reaching the fruit. There is plenty of calcium in the soil but it’s not released fast enough to satisfy a huge demand for calcium by the fruit.
            The only way to correct this problem is with calcium sprays. The calcium from the spray is absorbed directly by the fruit.
            In pears, this problem is called “Corky Spot”. In apples, it is called “Bitter Pit”. Corky Spot and Bitter Pit develops on fruit from older trees that have been harvested for many years. Brown spots develop in the flesh of pear and apple fruit because of a calcium deficiency inside the fruit.
Bitter pit on 'Mutsu' apple
            Fruits, full of calcium, are removed from the trees. A rapid uptake of calcium from soil by tree roots causes a “void” of calcium in the soil. Calcium is needed by the next crop of fruit the following year but it’s not available. 

Information on corky spot from Washington State University
            To solve this problem, we “feed” the tree calcium “backwards”; force the calcium inside the fruit by spraying the fruit rather than relying on tree roots. It may not make much sense when the soil is so chock full of calcium but spraying the tree with calcium is the only way to get rid of these brown spots.
            Calcium sprays are applied to the tree with most of the spray landing on the fruit. The most effective sprays are from calcium chloride dissolved in water. A wetting agent is added to the mixture to improve calcium absorption inside the fruit. These sprays are applied 5 times each year as the fruit is enlarging. 

Use 1 pound of food grade calcium chloride dissolved in 100 - 200 gallons of water (you do the math for a backpack sprayer). Add a wetting agent to the spray to help the calcium enter the fruit. Spray only until it begins to run off the fruit. Do it during a cool time of day. No, it will not burn the leaves at this concentration if  you do it in the early morning in the summer.

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