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Hot Water Seed Treatment

Hot Water Seed Treatment

About Hot Water Seed Treatment

Benefits of hot water seed treatment: Some plant pathogens are able to penetrate and survive within the seed, out of reach of surface seed treatments. They include many bacterial pathogens of vegetables as well as fungi, oomycetes, and viruses. 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 prevented. Even though pathogens do not survive well in soil once infected crop residues have decayed, they can be difficult to manage once established on a farm. Hot water seed treatment also has the beneficial effect of priming seeds resulting in faster germination than untreated seed.  Hot water seed treatment is a valuable tool for preventing establishment of seed-borne diseases on the farm, or their reintroduction year after year.

Deciding which seeds to treat: To decide whether to use heat treatment, first determine the likelihood that seed-borne pathogens could be present based on the crop (see Table 1). 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.

Treatment procedure and seed requirements: The temperature of water for treating seed varies from 115 to 125°F, depending on the crop, and the treatment period varies from 10 to 60 minutes. Large-seeded crops (beans, cucurbits, peas, corn etc.) cannot be effectively disinfested with hot water treatment because the temperature required to heat the whole seed inside and out would kill the outer seed tissue and the seed will not germinate. Chemically-treated or pelleted and primed seed also cannot be hot water treated. Treating seed saved for more than one year or seed saved from a heavily infested field may inhibit germination. Treat no more seed than you think you will use in the course of a season, as hot water treated seed may not remain viable for as long as untreated seed. It is important to use the appropriate protocol for each crop to control pathogens without damaging the seed. While hot water seed treatment can be done effectively on a stovetop in a large pot with an accurate thermometer and careful temperature control, it is much better to use a precision water baths that provide an even, stable and accurate temperature.

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


Diseases Controlled


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

Beet / Swiss Chard

Phoma/Canker, Downy Mildew, Cercospora leaf spot


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


Anthracnose, Early blight, Phomopsis, Verticillium wilt


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


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


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


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


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 Submission Form


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