Sally A. Miller
Melanie L. Lewis Ivey
One of the ways plant pathogens are introduced into a crop is on seeds. Bacterial pathogens are particularly notorious for this means of dissemination. In general, the earlier a pathogen comes in contact with the crop, the greater the potential for a serious disease problem to develop. This is why it is very important to start with “clean” seed. Clean seed can be obtained by applying one of the treatments described below to kill bacterial pathogens on and/or within the seed.
When treating vegetable seeds it is critical to follow the instructions exactly, as seeds may be damaged by the treatment and/or the pathogen may not be completely eliminated. In addition, old or poor quality seed can be injured by seed treatments. Therefore, it is recommended that a small sample be treated and tested for germination (see method below) prior to treating the entire seed lot. Treatments should be done on raw seed only, since the treatment will destroy any seed pelleting and will wash off any fungicide that may have been applied to the seed. If fungicide treated seeds are used, the fungicide washed off must be disposed of properly. After the treatment, seed may be treated with Thiram to prevent damping-off caused by various soilborne fungi.
Properly used, hot water treatment kills most bacterial disease-causing organisms on or within seed. This treatment is suggested for seeds of eggplant, pepper, 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.
Step 1: Wrap seeds loosely in a woven cotton bag (such as cheesecloth) or nylon bag.
Step 2: Pre-warm seed for 10 minutes in 100°F (37°C) water.
Step 3: Place pre-warmed seed in a water bath that will constantly hold the water at the recommended temperature (see table that follows). Length of treatment and temperature of water must be exactly as prescribed.
Step 4: After treatment, place bags in cold tap water for 5 minutes to stop heating action.
Step 5: Spread seed in a single, uniform layer on screen to dry. Do not dry seed in area where fungicides, pesticides, or other chemicals are located.
Step 6: Dust seed with Thiram 75WP (1 tsp/1 lb seed) once the seed is completely dry.
|Brussels sprouts, eggplant, spinach, cabbage, tomato||122||50||25|
|Broccoli, cauliflower, carrot, collard, kale, kohlrabi, rutabaga, turnip||122||50||20|
|Mustard, cress, radish||122||50||15|
|Lettuce, celery, celeriac||118||47||30|
Chlorine treatment effectively removes bacterial pathogens on the seed surface. Unlike hot water treatment it does not eliminate pathogens within the seed. Chlorine treatment is recommended for both large- and small-seeded vegetables if the seeds have not been treated by any other method and the possibility of pathogens being carried inside the seeds is not a concern.
Step 1: Agitate seed in a solution of 25 oz Clorox plus 100 oz water with one teaspoon surfactant for 1 minute. Use 1 gallon of disinfectant solution per pound of seed (conversions provided below) and prepare a fresh solution for each batch.
Step 2: Rinse seed thoroughly in cold running tap water for 5 minutes.
Step 3: Spread seed in a single, uniform layer on screen to dry. Do not dry seed in area where fungicides, pesticides, or other chemicals are located.
Step 4: Dust seed with Thiram 75WP (1 tsp/1 lb seed) once the seed is completely dry.
|8 oz = 1 cup|
16 oz = 1 pint
32 oz = 1 quart
128 oz = 1 gallon
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Keith L. Smith, Associate Vice President for Agricultural Administration and Director, OSU Extension TDD No. 800-589-8292 (Ohio only) or 614-292-6181