Ohio State University Extension Fact sheet

Ohio State University Extension Fact Sheet

Plant Pathology

2021 Coffey Road, Columbus, Ohio 43210

Hot Water and Chlorine Treatment of Vegetable Seeds to Eradicate Bacterial Plant Pathogens

HYG-3085-05

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.

Hot Water Treatment

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.

Instructions

  1. The following equipment and supplies are needed to hot water treat vegetable seed.

  2. How to Hot Water Treat Seed.
    Step 1: Wrap seeds loosely in a woven cotton bag (such as cheesecloth) or nylon bag.

    Seeds lying on a loose-weave cloth.           Corners of the cloth have been gathered together to form a pouch for the seeds.

    Step 2: Pre-warm seed for 10 minutes in 100°F (37°C) water.

    Picture of a machine used to heat water.          Picture of a machine showing 37.8 degrees celsius          A picture of the seed bundle in the beaker of heated 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.

    A picture of the same machine again.          A picture of the machine heated to 50.3 degrees celsius.          A picture of the seed bundle in the beaker of heated water, with a thermometer.

    Step 4: After treatment, place bags in cold tap water for 5 minutes to stop heating action.

    A picture of the seed bundle submerged in the beaker of heated water.

    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.

    A picture of the wet seeds resting on the opened cloth.          A picture of the seeds spread out on a drying screen.

    Step 6: Dust seed with Thiram 75WP (1 tsp/1 lb seed) once the seed is completely dry.

    A picture of the now dry seeds on the screen with a measured quantity of the Thiram lying next to them.
Seed Water temperature Minutes
°F °C
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
Pepper 125 51 30
Lettuce, celery, celeriac 118 47 30

Chlorine Treatment

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.

Instructions

  1. The following equipment and supplies are needed to chlorine treat vegetable seed.

  2. How to Chlorine Treat Seed.
    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.

    A picture of a bottle of Clorox next to a graduated cylinder with a measured amount of Clorox.          An electronic scale measuring a quantity of seeds.          A picture of the seeds mixed into the Clorox and water solution in a glass beaker.

    Step 2: Rinse seed thoroughly in cold running tap water for 5 minutes.

    A picture of the seeds in a strainer being rinsed under running water.

    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.

    A picture of the resting on a cloth.          A picture of the seeds spread out on a drying screen.

    Step 4: Dust seed with Thiram 75WP (1 tsp/1 lb seed) once the seed is completely dry.

    A picture of the now dry seeds on the screen with a measured quantity of the Thiram lying next to them.

How to Test for Seed Germination After Hot Water or Chlorine Treatment

  1. Mix seeds in each seed lot and count out 100 seeds per seed lot.
  2. Treat 50 of the seeds exactly as described in the fact sheet.
  3. After treated seeds have dried, plant the two groups of seeds separately in flats containing planting mix according to standard practice. Label each group as “treated” or “untreated.”
  4. Allow the seeds to germinate and grow until the first true leaf appears (to allow for differences in germination rates to be observed).
  5. Count seedlings in each group separately.
  6. Determine the % germination in each group: # seedlings emerged ÷ # seeds planted x 100.
  7. Compare % germination in each group: they should be within 5% of each other.

Conversions:

8 oz = 1 cup
16 oz = 1 pint
32 oz = 1 quart
128 oz = 1 gallon

Click here for PDF version of this Fact Sheet.

OSU Extension embraces human diversity and is committed to ensuring that all educational programs conducted by Ohio State University Extension are available to clientele on a nondiscriminatory basis without regard to race, color, age, gender identity or expression, disability, religion, sexual orientation, national origin, or veteran status.

Keith L. Smith, Associate Vice President for Agricultural Administration and Director, OSU Extension TDD No. 800-589-8292 (Ohio only) or 614-292-1868


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