Vegetable Seed Treatment

Diseases of vegetable crops often are caused by fungi, oomycetes, or bacteria carried on, in, or with the seed. Some types of seed, such as sweet corn and field corn, may carry extremely high levels of potential pathogens. Nearly all seed of certain corn lots have been found to be carrying strains of Fusarium species known for their ability to incite diseases on corn. Not all infected seed will necessarily transmit disease to germlings or seedlings, however, because the outcome for a seedborne pathogens is usually strongly influenced by environmental conditions, including temperature effects on the pathogen and the plant, soil moisture levels, microbial competition after planting, soil chemistry, and potential pesticide applications. Disinfecting seed using hot water or chemical disinfectants to kill these potential pathogens is important in preventing introduction of pathogens into a production area as well as protecting crops in the current cycle from disease losses. Addition of chemicals or biological control agents onto the seed surface or seed bed help to protect seeds as well as developing seedlings from decay or damping-off caused by soilborne organisms.

Seed treatments alone cannot always be relied on to control all diseases against which they are directed. They are not panaceas of all ills. Sometimes a seed treatment will of itself be entirely effective in preventing disease, but more often it is only one step in a series of disease control practices. Disease-causing organisms harbor in places besides seed, such as old crop refuse in the seedbed, greenhouse, or field, or sashes and frames, in soil, and on weeds closely related to the crop. Therefore, cultural control practices such as seedbed and field sanitation to encourage the breakdown of infected crop residues, rotation, destroying weed carriers, and possibly the incorporation of a fungicide program for disease management can all be part of secure, successful disease control. But without treating seeds to prevent entry of pathogens that seed may introduce, commercial producers and home-gardeners alike are at risk for repeated introductions of diseases, including types where pathogens subsequently persist in the soil, such as Fusarium diseases.

How to Treat Seed with Hot Water

Hot water treatments will aid in general control of seedborne pathogens on crucifers, carrot, celery, eggplant, lettuce, onion, parsnip, pepper, spinach, and tomato. It will aid in controlling fungi such as Alternaria, Fusarium, and Verticillium as well as bacteria including Xanthomonas and Pseudomonas. Hot water treatment is recognized to be as effective as fungicides for controlling black leg of crucifers.

  1. Pre-warm seed in water at 100°F for 10 minutes.
  2. Soak seed in hot water maintained at 122°F for the prescribed treatment time (example: 20 minutes for many Brassica crops).
  3. Cool seed in running water for 5 minutes.
  4. Dry seed.

Caution Do not exceed the recommended high temperature while treating seed in order to preserve seed viability, don’t go at a cooler temperature because pathogens won’t be killed. Hot water treatment done at the proper temperature kills much of the pathogen population on seeds and seed lots with good germination rates prior to treatment should retain good germination rates after treatment. Studies done during 2015 at Oregon State University showed that hot water-treated seed maintained germination as good as or better than the nontreated seed for at least one year after treatment.

See Ohio State University extension fact sheet (HYG-3086-05) at https://www.oardc.ohio-state.edu/sallymiller/extension/factsheets/organi... for more information, including prescribed hot water treatment times for a range of vegetable crops.

How to Treat Seed with Fungicides

  1. To treat small quantities of seed, use appropriately-labeled fungicides. Shake seed and fungicide together 3 to 5 minutes in jars or cans (not over half full) with tight-fitting lids. For small packets, add a small amount of fungicide to seed in the packet and shake well. For larger quantities of seed, use a rotary or mechanical mixer. Slurries often are more convenient for treating large amounts of seed.
  2. If the seeds you buy were treated by the seed dealer or someone else, do not treat seeds again.

Caution Most fungicides are either poisonous or noxious and must be handled with care. Follow manufacturer’s label directions for handling fungicide and treated seeds. Avoid breathing excessive amounts of fumes. Use a mask if treating large quantities of seed. Do not permit children, pets, or livestock to have access to the fungicide or to treated seed. Do not feed treated seed to livestock.

How to Treat Seed with Biological Control Agents

  1. Small quantities of seed can be treated with appropriately-labeled biological dusts in a manner similar to step 1 of “How to Treat Seed with Fungicides” above. Many of the biologicals are applied to soil or growing media rather than to seed.
  2. If the seeds you buy were treated by the seed dealer or someone else, do not treat seeds again.

Caution Most biological control agents are sensitive to environmental conditions during storage and must be handled with care. Avoid storage at hot temperatures. Follow manufacturer’s label directions for handling biological agent and treated seeds. Do not permit children, pets, or livestock to have access to the treated seed. Do not feed treated seed to livestock.