Insight on Blight Can Help Protect Your Pepper Crop

Insight on Blight Can Help Protect Your Pepper Crop

Closeup of blight of pepper

Blight of pepper can impact all parts of the plant. Photo by Yonghao Li

Losses from Phytophthora capsici have consistently affected pepper producers in Florida for many years. Phytophthora blight of pepper is extremely damaging and can result in a total loss of the crop prior to the first harvest. The host range of P. capsici is wide and includes a number of vegetables, including cucumber, cantaloupe, eggplant, green bean, squash, tomato, and watermelon. Diseases caused by P. capsici are referred to as Phytophthora blight.

Identification
Plants can be infected at any time during the season, and all parts of the plant can be infected. Phases of the disease include rotting of roots, crowns, and fruit, and blighting of leaves and stems. Seedling infections can result in damping off, with young plants dying quickly.

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On older plants, infections often occur first on crowns at or just above the soil line. Stem lesions are dark brown to black and result in girdling and plant death. Infected roots appear dark brown and mushy.

Under rainy conditions, splashing water can spread the pathogen into the upper canopy leading to stem lesions and fruit infections. Leaf infections are not as common but can occur showing up as circular lesions with tan margins and brown centers.

Fruit rot appears as dark-green, water-soaked areas. Under humid conditions, infected fruit may be covered with white mycelia, which resembles a dusting of powdered sugar. Sometimes fruit can become infected in the field, but symptoms do not show until after harvest when the fruit is headed to market.

Survival and Spread
P. capsici spreads by movement of soil or water. The pathogen also is spread by wind or splashing water as sporangia. Sporangia can either germinate directly and infect pepper tissue, or they can produce motile zoospores that can swim in films of water and initiate multiple infections.

Disease typically occurs during wet weather and in low, waterlogged areas of fields. Excessive rainfall, coupled with standing water, creates ideal conditions for epidemics. Phytophthora can rapidly affect entire fields. Under ideal conditions, the disease can progress rapidly, and symptoms can occur three to four days after infection.

Management Methods
Control of Phytophthora blight is difficult if the pathogen is present and conditions are favorable.

The best way to manage the disease once the pathogen is present is to use an integrated program of crop rotation, water management, soil management, the use of resistant cultivars, and fungicide applications.

Preplant fumigation may help reduce the incidence of disease but is not particularly effective.
Resistant cultivars are available and help protect against the crown rot phase of the disease but will not provide protection against the foliar phases.

Effective, labeled fungicides should be used preventively according to label instructions. It is essential that fungicides with different modes of action be rotated to prevent the buildup of fungicide resistance in P. capsici.