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Hot Water Seed Treatment

Hot Water Seed Treatment

Some plant pathogens, including specific fungal, oomycete, and viral pathogens, can be carried on seed; some can only infest the seed surface, but others are able to penetrate the seed coat and survive within the seed. In both cases, the pathogen can then grow with the seed when it is planted, resulting in an infected plant. Therefore, starting with disease-free seed is an important step towards growing disease-free crops. Seeds can be treated with chlorine or pesticides to eliminate pathogens that are associated with the surface of seeds. However, these treatments cannot penetrate the seed coat, and therefore leave internal pathogens untouched. Hot water can penetrate the seed coat and can also kill pathogens, making it a useful tool for managing seed-borne pathogens.

Treating your seeds with hot water can help prevent the establishment of seed-borne diseases on your farm, or prevent their reintroduction year after year. However, it’s important to note that while hot water seed treatment will kill pathogens on and within your seeds, it does not protect crops from disease and does not guarantee disease-free crops. Crop rotation and field sanitation are key for preventing diseases that overwinter on crop debris, and crops need to be scouted regularly for wind-, water-, and insect-borne diseases.

Hot water seed treatment has the beneficial effect of priming seeds, resulting in faster germination than untreated seed. However, the treatment can decrease germination rates, especially of older seed (more than 1 year old) or seeds that were grown under stressful environmental conditions. Treated seed does not remain viable for as long as untreated seed and should be planted during the growing season immediately following treatment.

Deciding which seeds to treat

To decide whether to use hot water treatment, first determine the likelihood that seed-borne pathogens could be present based on the crop (see Table 1 for reference). Tomato, pepper, and brassicas are good candidates for hot water seed treatment because there are common bacterial and fungal diseases of these small-seeded crops that can be easily killed through treatment. Next, ask your seed supplier if the seed was produced in a way to minimize exposure to seed-borne pathogens and if the seed was tested for their presence. Find out if the seed has already been treated with hot water or if it has been primed (pre-soaked to promote earlier and more uniform germination), as treating again could adversely affect the seed. You should also not treat seed that has a fungicide or insecticide treatment coating, as it will wash off during treatment. Only a few companies routinely hot-water treat seeds—many are reluctant because there is a risk that germination rate will drop if the water is too hot or if the seeds were already exposed to stressful environmental conditions.

Large-seeded crops (beans, cucurbits, peas, corn etc.) are usually not effectively disinfested with hot water treatment because the temperature required to heat the whole seed would kill the outer seed tissue and the seed will not germinate. In some cases, hot water has been used to disinfect just the surface of larger seeds, for example, treating anthracnose on beans.
 

Table 1. Vegetable crops and seed borne pathogens control by hot water treatment.

Crop

Diseases Controlled

Brassicas

Alternaria leaf spot, Bacterial leaf spot, Black leg, Black rot

Beet / Swiss Chard

Phoma/Canker, Downy Mildew, Cercospora leaf spot

Carrot

Alternaria leaf blight, Bacterial leaf blight, Cercospora leaf spot, Crater rot/foliar blight

Celery / Celeriac

Bacterial leaf spot, Cercospora leaf spot, Septoria leaf spot, Phoma crown and root rot

Eggplant

Anthracnose, Early blight, Phomopsis, Verticillium wilt

Lettuce

Anthracnose, Bacterial leaf spot, Lettuce mosaic virus, Septoria leaf spot, Verticillium wilt

Onion

Purple blotch, Stemphylium leaf blight, Basal Rot, Botrytis blight, Smudge, Black mold

Pepper

Anthracnose, Bacterial leaf spot, Cucumber mosaic virus, Pepper mild mosaic virus, Tobacco mosaic virus, Tomato mosaic virus

Parsley / Cilantro

Bacterial leaf blight, Alternaria leaf blight, Black rot, Cercosporoid leaf blight, Septoria blight

Spinach

Anthracnose, Cladosporium leaf spot, Cucumber mosaic virus, Downy mildew, Fusarium wilt, Stemphylium leaf spot,Verticillium wilt

Tomato

Alfalfa mosaic virus, Anthracnose, Bacterial canker, Bacterial speck, Bacterial spot, Cucumber mosaic virus, Early blight, Fusarium wilt, Leaf mold, Septoria leaf spot, Tomato mosaic virus, Verticillium wilt, Double virus streak

Hot Water Seed Treatment Service

The UMass Extension Vegetable Program offers a hot water seed treatment service. Seed submissions are treating using established and tested protocols for each crop species and cultivar to ensure the highest quality. Submissions are generally treated and returned to the submitter within 10 days of receipt. For urgent submissions or for a more specific timeline, please contact us before sending your seed.

Seed treated by the UMass Extension Vegetable Program is for grower use only and not for resale or distribution.

To submit seeds for hot water seed treatment, please complete the form below. Send the seeds, along with the completed form and a check made out to 'UMass' to:

UMass Vegetable Program
230 Stockbridge Rd.
French Hall Room 306
Amherst, MA 01003

Hot Water Seed Treatment Liability Waiver

Questions?

Please contact the UMass Extension Vegetable Program at umassveg@umass.edu or (413) 577-3976.