The appearance of brown spots on pepper plants or fruit is a common alarm signal for home gardeners, indicating that the plant is under some form of stress. These spots are not a single disease but rather a symptom pointing toward a range of underlying issues that can be environmental, infectious, or related to pests. Correctly identifying the specific visual characteristics of the spot is the first step in diagnosing the problem. Understanding the cause is necessary to determine if the spot is purely cosmetic, a sign of nutritional imbalance, or evidence of a spreading disease that threatens the entire crop.
Spotting the Signs of Environmental Stress
Brown spots can frequently be traced back to non-living factors, often related to weather or nutrient management. A common issue on the fruit itself is sunscald, which appears as a large, bleached, or sunken area on the side directly exposed to intense sunlight. The damaged tissue eventually turns whitish-tan and develops a papery texture, making it susceptible to secondary decay.
Another highly recognizable environmental issue is blossom end rot (BER), which presents as a large, dark, sunken patch on the very bottom, or blossom end, of the pepper fruit. This condition is not a true rot but an inability of the plant to translocate calcium to the developing fruit cells. BER is primarily triggered by inconsistent soil moisture, such as alternating cycles of wet and dry soil, which disrupts the plant’s uptake of calcium.
Brown spots can also appear on the foliage due to a condition called edema, which is a physiological disorder. Edema occurs when the roots rapidly absorb water faster than the leaves can transpire it, causing internal cell walls to burst. The symptom manifests as small, blister-like or raised spots, often on the undersides of leaves or on stems, that eventually turn a corky, light brown color.
Identifying Pathogen-Based Diseases
Infectious agents, particularly bacteria and fungi, cause distinct brown spots that spread under warm and humid conditions. One of the most damaging bacterial diseases is bacterial leaf spot, caused by Xanthomonas species. On pepper leaves, this appears as small, dark, circular spots that sometimes have a subtle yellow halo, but often the spots look dark and water-soaked.
The lesions caused by bacterial leaf spot can also be found on the fruit, where they are small, raised, and scab-like in texture. These bacterial spots do not result in immediate fruit rot but can make the fruit unmarketable. The bacteria spreads easily via splashing water, which is why overhead irrigation and wet foliage are conducive to the disease.
Fungal pathogens create different visual signatures, such as Anthracnose, caused by Colletotrichum species, which targets the fruit. This disease creates circular, dark brown, sunken lesions on the pepper’s skin. In moist weather, a characteristic pink or orange mass of fungal spores often develops in the center of the sunken spot, clearly distinguishing it from sunscald or bacterial spots. Another common fungal issue is Cercospora leaf spot, sometimes called Frogeye spot, which primarily affects older leaves. The spots are circular or angular brown lesions featuring a distinct tan, gray, or white center surrounded by a dark brown or purplish border.
Insect Damage and Secondary Issues
Insects rarely cause a simple brown spot directly, but their feeding activity often leads to brown markings through physical damage or secondary infection. Chewing insects, such as armyworms or corn borers, may tunnel into the pepper fruit, creating a wound that scabs over brown or provides an entry point for rot organisms. The resulting brown decay is a secondary symptom.
Sucking insects use piercing mouthparts to feed on plant cell contents, which can result in a bronze or stippled appearance on leaves that looks brown from a distance. Thrips, for instance, leave behind tiny black specks of fecal matter, known as frass, which contributes to the spotted or discolored look of the foliage. Similarly, aphids excrete a sticky substance called honeydew, which serves as a food source for sooty mold, a fungus that grows on the leaf surface and creates a layer of black or dark brown discoloration.
Stink bugs are another common pest that damages the fruit by injecting digestive enzymes during feeding. This results in initially light-colored, slightly sunken spots on the fruit surface, referred to as cloud spots. Underneath the skin, the damaged tissue turns into a corky, whitish-brown area that can later decay, resulting in a firm brown necrotic area.
Comprehensive Management and Recovery
Addressing environmental factors often requires adjusting cultivation practices to stabilize the growing environment. To combat blossom end rot, consistent, deep watering is preferred over frequent, shallow watering to ensure steady calcium uptake. Providing afternoon shade or using a shade cloth can prevent sunscald on fruits, especially when the leaf canopy is sparse.
Managing pathogen issues relies heavily on sanitation and moisture control to limit the spread of infectious spores and bacteria. Immediately removing and destroying infected leaves and fruit helps reduce the amount of disease inoculum. Avoiding overhead watering, which splashes spores and keeps foliage wet, and improving air circulation through proper plant spacing are effective cultural controls.
For severe bacterial issues, applying a fixed copper spray can help slow the spread of the disease on new growth. Fungal diseases may require a targeted fungicide application, but crop rotation is necessary for both types of pathogens to prevent them from overwintering in the soil. Long-term prevention involves selecting resistant pepper varieties when starting seeds.
Pest control can begin with non-chemical methods. Horticultural oils or insecticidal soaps can be applied to manage persistent populations of sucking pests.
Pest Control Methods
- Physically removing larger pests.
- Using a strong jet of water to knock off smaller insects like aphids.
- Applying horticultural oils or insecticidal soaps to manage persistent populations of sucking pests such as thrips or mites.
- Using reflective mulch to deter certain flying insects by confusing them.