Hot water treatment
Hot water treatment controls many seed-borne diseases by using temperatures hot enough to kill the organism but not quite hot enough to kill the seed. It must be done carefully and accurately. A few degrees cooler or hotter than recommended may not control the disease or may kill the seed.
Hot water treatment can be damaging or not practical for seeds of peas, beans, cucumbers, lettuce, sweet corn, beets and some other crops. Some hybrid varieties of cauliflower may be damaged by the recommended treatment. Seeds that can be treated by hot water are listed in Table 1.
| Vegetable | Temperature | Time (minutes) | Diseases controlled |
|---|---|---|---|
| Cabbage | 52oC | 30 | Black rot, bacterial leaf spot, black leg, damping-off, ring spot |
| Broccoli | 50oC | 20 | Black rot, bacterial leaf spot, black leg, damping-off, ring spot |
| Brussels sprouts | 50oC | 20 | Black rot, bacterial leaf spot, black leg, damping-off, ring spot |
| Cauliflower | 52oC | 25 | Ring spot |
| Tomato | 56oC | 30 | Damping-off, bacterial canker, speck and spot |
| Celery | 50oC | 30 | Blights, damping-off |
| Carrot | 50oC | 20 | Alternaria, bacterial blight |
| Pumpkin | 55oC | 15 | Fusarium |
Hot water treatment of fresh seed at the temperatures recommended should not reduce germination. However, check seed packets carefully to ensure that the seed has not already been treated by the seed company. Seed should not be treated twice. Treating old seed will reduce germination.
Follow these steps for accurate treatment. Figure 1 shows the equipment needed.
- Put a few grams of seed in a small porous bag, such as cheesecloth. The amount of seed should be just sufficient to allow thorough and immediate wetting. The bag may need to be weighted down.
- Fill an insulated container with water slightly hotter than the temperature required (see Table 1). Use an accurate thermometer to check the temperature and immerse the thermometer to half way down the container.
- When the water reaches the correct temperature, wet the bag and seed with warm water and suspend them in the container of water.
- Stir the water and the bag of seed regularly during treatment to ensure that all the seed is heated evenly. Check the temperature regularly and add just enough hot water to maintain the temperature needed.
- Spread the seed out to dry in a thin layer on paper in a shady area.
- Plant the seed as soon as it is thoroughly dry. Do not store treated seed.
