Gordon Johnson, Extension Vegetable & Fruit Specialist; email@example.com
As fall approaches and late pepper crops mature, pepper stip disorder can be a problem in bell, pimento, and elongated peppers (chilies, bananas, sweet frying types) causing them to be unmarketable. It is particularly a problem on peppers taken to ripe stage such as red bells, but can also be an issue on green immature fruit. Pepper stip, also called color spotting or black spotting, is a physiological disorder of pepper fruit. It causes gray, brown, black, or green spots that are slightly sunken and are ¼ inch or smaller in diameter. Spots may be single or in groups and can resemble damage from stink bugs. Microscopic examination of affected areas shows dead collapsed cells with no evidence of cell puncture or insect damage. It is primarily a fall disorder and occurs most often when temperatures drop into the 40s and 30s. It can also occur after peppers are moved into cold storage. This is similar to what is seen with blossom end rot, only the affected areas are isolated and can occur throughout the fruit, not just on the ends.
The exact cause of stip is not known; however, it is thought to be a nutrient imbalance involving lower calcium (Ca) in fruit and high levels of nitrogen (N) and potassium (K). Research has shown that stip was most common in fields with low soil calcium or low pH and in fields with very high N and K fertilization.
Pepper varieties vary considerably in their susceptibility to stip. Research has shown that resistant cultivars consistently had lower N and K, and higher Ca concentrations than susceptible cultivars in leaf or fruit tissue samples. In 2011 red bell pepper variety trials conducted in New Jersey by Rutgers University, it was found that Camelot, Paladin, Classic, Patriot and Vanguard all were susceptible to stip. Additional trials are underway this fall.
In late summer and fall, there is reduced transpiration, and Ca movement in the fruit can be reduced. Excess N can cause rapid growth and extra foliage further limiting fruit transpiration and excess K can compete with Ca for plant uptake and cation exchange in the fruit.
Managing stip starts with using resistant varieties for fall production. Maintain high soil calcium levels and reduce nitrogen and potassium in fall production. Additional calcium through the drip system may help reduce stip. Foliar calcium applications have shown little or no effect on reducing stip.