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What Causes Pepper Stems to Turn Black?
Sep 12,2026
Several diseases and nutritional problems can cause pepper stems to turn black.
Common causes include Phytophthora blight, bacterial soft rot, sclerotinia disease, gray mold, streak virus disease, nutrient imbalance involving nitrogen, phosphorus, and potassium, and micronutrient deficiencies.
Except when stem discoloration is caused by nutrient deficiencies, the other five stem diseases can generally be distinguished by examining the characteristics of the lesions.
1. Identify the Disease by Lesion Color
The lesions caused by Phytophthora blight are usually dark brown or blackish-brown.
Lesions caused by bacterial soft rot, sclerotinia disease and gray mold are lighter in color, usually light gray-white or gray-brown.
Lesions associated with streak virus disease are generally light gray-yellow.
2. Identify the Disease by Whether the Lesions Are Sunken
Lesions caused by bacterial soft rot, sclerotinia disease and gray mold are generally not sunken.
Lesions caused by Phytophthora blight may be slightly sunken, while those associated with streak virus disease are noticeably sunken.
3. Identify the Disease by the Presence of Mold Growth
Dense gray mold on the lesions is characteristic of gray mold.
Dense white mold followed by the formation of black sclerotia is characteristic of sclerotinia disease.
Under humid conditions, sparse white mold may develop on lesions caused by Phytophthora blight.
No visible mold growth is generally observed with bacterial soft rot or streak virus disease.
4. Identify the Disease by the Moisture of the Lesions
Lesions that are wet and appear water-soaked or ooze a soft, fluid-like substance are characteristic of bacterial soft rot.
Dry, sunken lesions are associated with streak virus disease.
Lesions caused by gray mold, sclerotinia disease and Phytophthora blight may initially appear wet and later become dry.
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