Pepper blight is a common and destructive plant disease that significantly impacts pepper plants. It can cause widespread damage and substantial losses for both home gardeners and commercial growers. Understanding pepper blight is important for maintaining healthy and productive pepper crops.
Identifying Pepper Blight
Pepper blight can manifest in various ways across different parts of the plant, often progressing rapidly.
On the leaves, initial symptoms may appear as small, water-soaked lesions that expand and turn a light tan color. These lesions can be irregular in shape and may lead to rapid blighting and collapse of the leaves, particularly during wet conditions. White, moldy growth might also be visible on the leaves during periods of high moisture.
The stems of infected pepper plants often develop dark, water-soaked areas near the soil line, turning brown to black. These lesions can girdle the stem, causing the plant to wilt and eventually die. White mold may also be observed on infected stems.
Pepper fruit is also susceptible to blight, with infection often occurring through the fruit stalk. Early fruit rot symptoms include dark green, water-soaked areas that later become covered with a white to gray mold. These lesions can expand, causing the fruit to shrivel and rot.
Causes and Spread of Pepper Blight
Pepper blight is primarily caused by the oomycete Phytophthora capsici, a fungus-like organism. This pathogen can lead to rapid crop destruction within a few days under favorable conditions. Another related pathogen, Phytophthora infestans, causes late blight in potatoes and tomatoes and shares similarities with P. capsici.
The pathogen thrives in warm temperatures (20 to 30°C / 68 to 86°F) and wet, humid conditions. It can persist in the soil for over 10 years, forming survival structures called oospores. Spread occurs through splashing water, such as rain or overhead irrigation, which carries contaminated soil particles to healthy plants. Infected seeds and tools can also spread the disease.
Preventing Pepper Blight
Preventive measures can reduce the risk of pepper blight.
- Crop rotation involves planting non-host crops like cereals (corn, wheat) in affected areas for at least four years to reduce pathogen levels in the soil. Avoid planting peppers in fields with a history of Phytophthora blight.
- Select pepper varieties with resistance or tolerance to Phytophthora capsici. Some bell pepper varieties with resistance include Paladin, Aristotle, Revolution, Conquest, Declaration, Emerald, and Isle.
- Ensure proper plant spacing for good air circulation, which reduces humidity around plants and discourages pathogen growth.
- Focus watering techniques on delivering water directly to the plant’s base, such as with drip irrigation, to minimize splashing and keep foliage dry.
- Improve soil drainage by using raised beds, ideally 6-7 inches high, to prevent waterlogging. Covering beds and furrows with small-grain mulches can also limit splash dispersal of spores.
- Regularly clean and sanitize garden tools after working with plants, especially those that may be infected, to prevent accidental pathogen transfer.
Managing Pepper Blight
Once pepper blight is identified, immediate action is needed to limit its spread. Remove and destroy infected plant parts or entire plants to reduce the source of inoculum. This prevents the pathogen from spreading to healthy plants.
For severe cases, fungicides can be used. Copper-based fungicides, such as copper hydroxide, are options for blight control. Other effective fungicides for P. capsici include ametoctradin + dimethomorph, cyazofamid, fluazinam, and mefenoxam. Apply fungicides before or after heavy rainfall and rotate products from different FRAC groups to minimize fungicide resistance. Always follow product instructions regarding dosage rates and pre-harvest intervals.