The appearance of black spots on jalapeño peppers can be alarming for any gardener, suggesting a serious problem with a developing harvest. These discolorations, however, do not always signal a disease that requires immediate intervention or the loss of the fruit. Understanding the precise cause is the first step, as the issue can range from a natural, harmless physiological reaction to a highly contagious pathogen. This article categorizes these causes and provides guidance on how to identify and manage each one.
Physiological Causes (The Safe Spots)
The most frequent reason for black markings on jalapeños is corking, which is a desirable sign of a robust pepper. Corking appears as small, horizontal, tan or black lines that resemble stretch marks or cracks on the pepper’s skin. These marks result from the fruit growing faster than its outer skin can stretch, causing the skin to crack and then heal with a darker, scarred tissue.
This rapid expansion is often triggered by inconsistent watering, specifically an influx of water after a dry period, which forces a sudden growth spurt. Corking is a welcome sight for many pepper enthusiasts because the stress that causes the cracking is also linked to increased capsaicin production, suggesting a hotter, more flavorful pepper. The marks are purely cosmetic and the pepper remains safe to eat.
Another non-contagious cause is edema, a disorder resulting from an imbalance in water absorption and transpiration. This occurs when the plant takes in water faster than it can release it through its leaves, often due to high humidity, cool temperatures, or poor air circulation. The excess pressure causes plant cells to swell, rupture, and collapse, leaving small, slightly raised, dark or brown spots on the fruit or the undersides of leaves. Edema does not spread and is simply a sign of environmental stress, not a disease.
Pathogen-Related Causes (The Problem Spots)
Black spots that are sunken, watery, or spreading rapidly are caused by infectious diseases and require prompt attention. The most common bacterial culprit is Bacterial Spot, caused by species of Xanthomonas, which is highly contagious and spreads easily through splashing water. On the pepper fruit, this infection manifests as dark, raised, rough, and wart-like scabs that may appear cracked on the surface. Affected leaves first show small, water-soaked spots that eventually turn dark brown or black, sometimes with a surrounding yellow halo, often leading to premature leaf drop.
Fungal infections like Anthracnose are a common cause of black spots, particularly in warm, wet, and humid conditions. This disease, caused by Colletotrichum species, presents on the fruit as circular, soft, and sunken lesions that start as water-soaked areas before turning tan, brown, or black. A key identifying feature of Anthracnose is the appearance of salmon-pink, orange, or black spore masses in the center of the sunken lesions, often arranged in concentric rings.
Alternaria leaf spot, primarily caused by Alternaria alternata, frequently appears secondary to other damage like sunscald or blossom end rot. These dark spots often colonize the injured tissue, creating a chocolate brown to black patch that may have a dark, felty growth under high humidity. Unlike the raised scabs of bacterial spot or the pink spore masses of Anthracnose, Alternaria spots are flat and irregularly shaped, indicating a generalized rot of the damaged tissue.
Safety and Management
The edibility of a pepper depends entirely on the cause of the black spots, making accurate identification essential. Peppers showing only corking or mild edema are safe to consume, as these are natural cosmetic blemishes with no impact on food safety. If the spots are caused by a severe bacterial or fungal infection, avoid eating the fruit, as the lesions compromise the skin and allow secondary pathogens to enter the flesh. If the infection is minor and localized, the pepper can be salvaged by cutting out the infected areas and cooking the remaining healthy tissue.
Prevention is the most effective management strategy against infectious black spots. Since most pathogens are spread by water splash, shifting from overhead sprinklers to drip irrigation or watering at the base of the plant is advised. Increasing air circulation by pruning lower leaves and spacing plants adequately helps reduce the prolonged leaf wetness that fungi and bacteria require to thrive. For confirmed bacterial spot outbreaks, a preventative spray schedule using a fixed copper fungicide may slow the spread. After the season, rotate the planting location away from any Solanaceous crops (like tomatoes or potatoes) for at least two to three years to prevent the overwintering of pathogens in crop debris.