WSU Tree Fruit Research & Extension Center

Tree Fruit Market Diseases

Saturday, February 16, 2019

WSU-TFREC/Postharvest Information Network/Tree Fruit Market Diseases/pearboron

Boron-deficiency pitting, earlier known as "drought spot", was a problem on certain varieties of pears grown in Washington and Oregon before the cause of the disease was discovered. The disease was first observed on Bartlett and Bosc and later found on Anjou. It is not known to occur on other varieties. Boron deficiency pitting is rarely seen on the market, now that boron is periodically added to the soil.

Early serious boron deficiency in the fruits may cause rough, corky areas with occasional cracking and russeting. Such seriously affected fruits, however, would never reach the market.

Typical pits that occur later in the development of the pears are shallow, flat-bottomed pits with straight sides. The pits appear as though they were formed by pressing the flat head of a nail into the fruit surface. Pits may be few or numerous, they are most abundant toward the calyx end. The pits are easily cut through with a knife. There is a relatively small amount of discolored, spongy tissue directly beneath them. These straight-sided, flat-bottomed pits (top photo) with a small mass of spongy tissue below (bottom photo) set boron-deficiency pitting distinctly apart from cork spot, with its large mass of corky tissue. They also set it apart from most examples of stony pit, with its mass of stone cells at the base of the pit. Small, poorly developed spots of stony pit on Anjou, however, might be temporarily confused with boron-deficiency pits, but the mass of stony cells at the base of even a small pit would resist cutting.

As pointed out, the cause of the pitting is a deficiency of available boron in the soil. Pears are much more tolerant of boron deficiency than apples. Pears never develop the extensive corky tissues in the core area and extending out into the flesh that are found in susceptible varieties of apples.

Boron-deficiency pitting is easily controlled by periodically adding boron to the soil. Follow the recommendations of the State agricultural extension service or experiment station.

Pear boron deficiency cork, external view
Pear boron deficiency cork, external view

Pear boron deficiency cork, internal view
Pear boron deficiency cork, internal view

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