Hot Water Seed Treatment for Control of Bacterial Spot of Scotch Bonnet Pepper

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Hot Water Seed Treatment for Control of Bacterial Spot of Scotch Bonnet Pepper


Figure 1a: Healthy fruit and seeds; Figures 1c: Fruit affected with bacterial spot. Figure 1d: Basic equipment for hot water seed treatment (hot plate, pot, thermometer and container for cooling of seeds)

Bacterial spot is the most common, and one of the most destructive diseases of peppers. Bacterial Spot Disease is caused by  Xanthomonas  campestris pv. vesicatoria . The most-important sources for bacterial spot are infested seed and diseased transplants.

The first strategy for controlling any disease is to eliminate or reduce the amount of the pathogen available to start the disease. Under favourable conditions one infested seed in a package of 10,000 could easily result in 100% diseased plants in the field. Use ONLY certified disease-free seeds or seeds that have been hot water treated. Hot water seed treatment is a very simple and effective method to control seed transmitted bacterial and some fungal pathogens. Hot-water treatment can kill bacteria inside and on the outside of seed. Freshly harvested seed withstand the heat treatment better than 1- or 2-year old seed.

It is essential to conduct a preliminary germination test with a small quantity of treated and untreated seed from each batch. Some seeds produced from stressed plants may not stand up to hot water treatment and germination may suffer (though this is rare with pepper seeds).

Seeds are soaked in hot water at 125°F (51°C) for 30 minutes. The temperature and length of treatment are important and should be carefully monitored. Use of a good laboratory thermometer is highly advisable. When using a hot plate, expect to spend some time adjusting temperature setting. Wait to begin treatment until the water temperature in the pot is maintained at a constant 122 o F/51°C. The seed may be held in loosely woven cheesecloth bags. After treatment, dip the bag in cold water to stop the heat treatment. Have containers of hot and cold water nearby in case the water temperature changes from 122 o F. Add a metal weight to keep the seed container submerged, but make sure it is not on the pot bottom.

How to Treat Seed With Hot Water

This method requires: -

  • Water bath or hot plate
  • Thermometer
  • Cotton cloth, cotton bags, or nylon bags
  • Screen for seed drying or paper towels

Check the temperature constantly and stir the water continuously. A wooden spoon works well when using a hot plate. Tape the thermometer to the wooden spoon so it does not touch the bottom of the pot. If temperature falls below 51°C, add hotter water while stirring; if temperature goes above 51°C, add cooler water while stirring.


Following the treatment avoid storing the seeds for extended period of time. After seeds are dried properly, treat (dust) with the recommended fungicide and then plant.

Hot water treatment is also suggested for seeds of eggplant, tomato, carrot, spinach, lettuce, celery, cabbage, turnip, radish, and other crucifers.

Seeds of cucurbits (squash, gourds, pumpkins, watermelons, etc.) can be damaged by hot water and thus should not be treated.



Water Temperature

Duration of treatment (minutes)

Brussels sprouts, eggplant, spinach, cabbage, tomato

122oF                      50oC


Broccoli, cauliflower, carrot, collard, kale, kohlrabi, rutabaga, turnip

122oF                          50oC


Mustard, cress, radish

122oF                           50oC



125oF                          51oC


Lettuce, celery, celeriac

118 oF                        47oC