Tiny brown spots on your apples? It might be bitter pit.
Bitter pit is a disorder of apples, related to low calcium levels. Also known as blotchy cork and Baldwin spot, this disease can also affect quince and pears.
Causes of bitter pit
Much like blossom end rot, bitter pit occurs when there is not enough calcium in a fruit. Calcium deficiencies in Bay Area soil are almost unheard of, but insufficient or irregular watering can make it hard for plants to get enough calcium where they need it. Once a plant puts absorbed calcium someplace, it is very difficult to move. This is called low mobility. Inadequate irrigation means newer leaves may look burnt or even die back, due to lack of calcium, regardless of how much is in the soil. The optimal range is 1000 to 1500 ppm; my soil test results showed that my soil contains over 2700 ppm.
Calcium in plants
Milk may help build strong bones and teeth in us, but the calcium it contains performs a surprising number of functions within a plant. Calcium is used by plants to metabolize other nutrients, strengthen cell walls, promote proper cell shape, protect against heat stress and many bacterial and viral diseases, regulates hormones, enzymes, and the stoma. Calcium levels also affect fruit quality.
How to control bitter pit
Many commercial growers spray trees with calcium, while others dip fruit in a calcium solution, but these methods are unrealistic for the home grower. The best way to avoid bitter pit in your apple crop is to irrigate regularly. Some research has shown that applying too much fertilizer, thinning fruit too early, and thinning too much can increase the odds of bitter pit occurring. Removing excessive vegetation without over pruning can help reduce the likelihood of bitter pit. My guess is that removing the extra leaves means there is more calcium for the rest of the tree.
Bottom line: those spongy little dead spots won’t hurt you. What they can do is create a point of entry for more serious pests and diseases that will require more effort on your part to resolve. You know, it’s one of those, “ounce of prevention” situations. Keep your trees healthy and treat them right to make your job easier.
You can grow a surprising amount of food in your own yard. Ask me how!
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