Bitter Pit

Tiny brown spots on your apples? It might be bitter pit.

Bitter pit is a disorder of apples. It is related to low calcium levels. Also known as blotchy cork and Baldwin spot, this disease can also affect quince and pears.

Early signs of bitter pit on lower left apple (Paebi) CC BY-SA 3.0

Causes of bitter pit

Much like blossom end rot, bitter pit occurs when there is not enough calcium in a fruit. Calcium deficiencies are almost unheard of west of the Rocky Mountains. Insufficient or irregular watering can make it hard for plants to move calcium to where they need it. Calcium is a low-mobility nutrient. It takes a lot of water to move calcium around once absorbed. Inadequate irrigation means newer leaves may look burnt or die due to a lack of calcium, regardless of how much is in the soil. The optimal range is 1000 to 1500 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. Plants use calcium to metabolize other nutrients, strengthen cell walls, promote proper cell shape, protect against heat stress and disease, and regulate hormones, enzymes, and the stoma. Calcium levels also affect fruit quality.

​Symptoms of bitter pit

Tiny brown spots can appear on either the skin or the flesh of an apple affected by bitter pit. These spots are dead tissue. And they look very appetizing, either. Symptoms start close to the flower end (calyx) and then spread.

Apple affected with bitter pit (Rasbak) CC BY-SA 3.0

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. Regular irrigation is the best way to avoid bitter pit in your apple crop. Applying too much fertilizer, thinning fruit too early, and thinning too much can increase the odds of bitter pit. Removing excessive vegetation without over-pruning can help reduce the likelihood of bitter pit. Maybe removing some foliage means more calcium for the rest of the tree. That's my guess, anyway.

Bottom line: those spongy little dead spots won’t hurt you. But they create points of entry for pests and diseases that create more work for you later. You know, one of those ounce-of-prevention situations. Keep your trees healthy and treat them right to make your job easier.