Hot Water Treatment of Seeds to Manage Certain Diseases in Vegetables

Emmalea Ernest, Scientist – Vegetable Crops;

Hot water treatment of seeds is a method to manage certain seed borne diseases of vegetable crops. This treatment has the benefit of killing pathogens on both the outside and the inside of the seed coat.

Some common examples of diseases managed this way include:

Cole Crops – black rot

Tomatoes – bacterial canker, bacterial speck, bacterial spot

Peppers – bacterial leaf spot

A more complete list of seeds that can be treated, treatment times and temperatures, and diseases controlled can be found at

The 2022/2023 Mid Atlantic Commercial Vegetable Production Recommendations include instructions for hot water seed treatment on page 129.

“Seed heat-treatment follows a strict time and temperature protocol, and is best done with thermostatically controlled water baths. Two baths are required: one for pre-heating and a second for the effective pathogen killing temperature. The initial pre-heat treatment is 10 minutes at 100ºF (38ºC). The effective temperature treatment and time in the second bath differ between crops; protocols for several important crops are listed in Table E-9.

Immediately after removal from the second bath, seeds should be rinsed with cool water to stop the heating process and dried on screen or paper. Seeds may be re-dusted with fungicide if desired. Pelleted seed is not recommended for heat treatment. Heat treat only seed that will be used during the current season. See crop sections for specific seed treatment recommendations.”

Hot Water Treatment Equipment Available for Use
The University of Delaware Extension Vegetable program has the equipment to hot water treat seeds. Please contact Emmalea Ernest to arrange to use the equipment.