eOrganic author:
Emily Gatch, Washington State University
This is an Organic Seed Resource Guide article.
Introduction
The purpose of any seed treatment is to improve seed performance in one or more of the following ways: 1) eradicate seedborne pathogens or protect from soilborne pathogens, 2) optimize ease of handling and accuracy of planting (reduce gaps in stand or the need for thinning of seedlings, particularly when mechanical planters are used), and 3) improve germination rates. In conventional production, seed is often treated with chemical fungicides which reduce seed and seedling losses due to seedborne and soilborne disease. Most seed protectants are not an option for organic growers; however, there are some seed treatments, such as priming, pelletizing, and the use of hot water or NOP-compliant protectants, that can be used by organic farmers to improve seed performance.
Certain crops are better candidates for seed treatment due to the nature of the seed (small or irregularly shaped) or the intended production regime. For example, pelleted seed is useful in head lettuce production because of the need for precision seeding, but is less advantageous for thick sowings of looseleaf lettuce in bed production.
Organic Seed Treatments
Priming
Primed seed has absorbed just enough water to dissolve germination inhibitors and activate the early stages of germination. Primed seed is therefore in a suspended state of growth, so it germinates faster and more uniformly over a broader temperature range, reducing the likelihood of very thick or thin plant stands. Priming results in earlier seedling establishment, which can aid in fending of the attack of damping-off pathogens to which germinating seedlings are particularly vulnerable. Priming is usually performed in conjunction with a pelleting process to protect the primed seed, which has a shortened life expectancy.
Pelleting
A seed pellet is a coating, usually of clay mixed with other inerts, that streamlines the size, shape, and uniformity of a small, non-round seed such as those of lettuce, carrots, onions, and many herbs and flowers. Pelleting results in easier, safer, and more accurate mechanical seeding, thus reducing gaps in the field and the need for labor-intensive thinning. Ideally, the pelleting materials are somewhat permeable to oxygen and absorb water quickly so that the pellet splits immediately upon hydration. Conventional pelleting techniques using synthetic inert materials are not approved for organic use, but there are now several pelleting materials on the market that are approved for use on organic farms.
Seed Health Treatments
This is a broad category of treatments that includes hot water, biological and plant extracts, bleach disinfection, and biologicals (microbes). These treatments can improve seed and seedling health by eradicating seedborne pathogens from the seed or protecting germinating seeds from attack by soilborne pathogens.
Hot water treatment
The use of hot water treatment to eradicate seedborne diseases, particularly those caused by plant pathogenic bacteria, is well-established. While the technique does not work for large-seeded vegetable crops, it has proven effective for brassicas, carrots, tomatoes, and peppers, and, to a lesser degree, celery, lettuce, and spinach. The typical procedure consists of: 1) warming the seed in 100°F water, 2) heating the seed for 20-25 minutes, depending on the crop species, in a 122°F water bath, 3) cooling the seed for 5 minutes in cold water, and 4) rapid drying. Precision in temperature and timing are important, as the seed embryo may be killed in hotter water or the disease incompletely eradicated in cooler water.
| Crop | Temperature | Duration | Notes |
| broccoli | 122 F | 20 min |
|
| kale | 122 F | 20 min |
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| mustards | 122 F | 20 min |
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| collards | 122 F | 20 min |
|
| turnip | 122 F | 20 min |
|
| cabbage | 122 F | 25 min |
|
| cauliflower | 122 F | 20 min |
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| Brussels sprouts | 122 F | 25 min |
|
| pepper | 122 F | 25 min | pepper may be more sensitive than tomato to hot water trt |
| tomato | 122 F | 25 min | can also try 125 F for 20 min |
| eggplant | 122 F | 25 min |
|
| carrot | 122 F | 20 min |
|
| celery | 122 F | 30 min |
|
| lettuce | 118 F | 30 min | lettuce is more sensitive; try small sample first and test viability |
Hot water treatment can cause a reduction in vigor over time, so hot water treated seed should not be kept for longer than a season. The procedure is described in detail in resources cited below. Some companies do their own hot water treatment or will custom hot water treatment upon grower request. If a lot is not treated by the company and no testing has been done for pathogen detection, growers may conduct their own hot water treatment with a home set-up. It should be noted that the company's liabilities are null and void if the grower treats the seed him/herself. Only fresh seed of high vigor should be subjected to hot water treatment, as old seed or seed of low vigor may respond poorly to the stress of the treatment and have reduced viability. Hot water treated seed should be used within one season; the storage life of the seed may be reduced by the treatment. For more information see the Ohio State University Extension Fact Sheet Hot Water and Chlorine Treatment of Vegetable Seeds to Eradicate Bacterial Plant Pathogens in Organic Production Systems (Miller and Ivey, 2005). See also the slide show Small-Scale Cost-Effective Hot Water Seed Treatment (Morton, Stearns and Andrews, 2016).
Plant extracts and oils
Evaluating plant extracts and oils as seed treatments is a new research area so there is currently little data on their efficacy. However, plant oils such as thyme, cinnamon, clove, lemongrass, oregano, savory, and garlic show some potential to suppress damping-off, and thyme oil is in use in Europe as a seed treatment. Pure soybean or mineral oils have been shown to reduce storage molds of maize and soybean. Further research on the disease suppressive potential of these oils is necessary to determine the viability of essential oil-based seed treatment protocols.
Bleach disinfection
Bleach (sodium hypochlorite) can be used to surface-disinfest seeds as an alternative to hot water. Bleach will eliminate pathogens on the seed surface but will not eliminate pathogens beneath the seed coat. Sodium hypochlorite is allowed for use on organic farms to disinfect wash water, provided that the levels not exceed the maximum residual contamination levels of the Safe Drinking Water Act, which currently is 4 ppm expressed as chlorine [40 CFR 141.65].
Biological seed treatments
Biological seed treatments, alone or in conjunction with priming and pelleting processes, may have potential in some situations for improving seedling health. In studies evaluating the efficacy of these microorganisms as seed treatments or drenches, results have been inconsistent.
Products that are currently commercially available include Kodiak (Bacillus subtilis, Bayer CropSciences), Mycostop (Streptomyces grieseoviridis, Verdera), SoilGard (Gliocladium virens, Certis), T-22 Planter Box (Trichoderma harzianum, BioWorks), Actinovate (Streptomyces lydicus, Natural Industries).
Additional Resources
- Morton, F., T. Stearns and N. Andrews. 2016. Small-scale cost-effective hot water seed treatment. Available at: https://mtvernon.wsu.edu/path_team/Small-scale%20Hot%20Water%20Treatment... (verified 5 Oct 2023).
- Raudales, R. and B. McSpadden, 2008. Microbial biopesticides for the control of plant diseases in organic farming [Online]. Ohio State University Extension Factsheet. Available at: https://ohioline.osu.edu/factsheet/SAG-18 (verified 23 Mar 2023).
- Hot water and chlorine treatment of vegetable seeds to eradicate bacterial plant pathogens [Online]. S. Miller and M. L. Ivey, 2005. Ohio State University Extension Bulletin HYG-3085-05. Available at: http://u.osu.edu/vegprolab/publications/grafting-publications/hot-water-... (verified 23 Mar 2023).
- Hot water and chlorine treatment of vegetable seeds to eradicate bacterial plant pathogens in organic production systems [Online]. S. Miller and M. L. Ivey, 2005. Ohio State Extension Bulletin HYG-3086-05. Available at:https://nwhortsoc.com/wp-content/uploads/2016/01/organicseedtrt.pdf (verified 23 Mar 2023).
- Preventing bacterial diseases of vegetables with hot water treatment [Online]. J. Boucher, G. Nixon, R. Hazzard and R. Wick, University of Connecticut. Available at:https://hortscans.ces.ncsu.edu/uploads/p/r/preventi_53bad03d6d56b.pdf (verified 23 Mar 2023).
- Seed treatments for organic vegetable production. Reports from the STOVE Project [Online]. Federal Biological Research Center for Agriculture and Forestry. Darmstadt, Germany. Available at: http://edepot.wur.nl/116019 (verified 23 Mar 2023).
Journal Articles
Some journal articles can be downloaded at no charge from the web. Others are only available through a university library. Try accessing articles by searching Google Scholar. If you cannot access any of these articles, request a copy from the corresonding author (obtain that information from the abstract, which can typically be found on the web).
- Effect of seed maturity on sensitivity of seeds towards physical sanitation treatments [Online]. S.P.C. Groot, Y. Birnbaum, N. Rop, H. Jalink, G. Forsberg, C. Kromphardt, S. Werner, E. Koch. 2006. Seed Science and Technology 34:403-413. Available at: http://www.ingentaconnect.com/content/ista/sst/2006/00000034/00000002/ar... (verified 23 Mar 2023).
- Efficacy of hot water and chlorine for eradication of Cladosporium variabile, Stemphylium botryosum, and Verticillium dahliae from spinach seed [Online]. L.J. du Toit and P. Hernandez-Perez. 2005. Plant Disease 89: 1309-1312. Available at: http://apsjournals.apsnet.org/doi/abs/10.1094/PD-89-1305 (verified 23 Mar 2023).
- Efficacy of bacterial seed treatments for controlling Pythium root rot of winter wheat. E. A. Milus and C.S. Rothrock. 1997. Plant Disease 81:180-184.
- Hot water treatment of carrot seeds: effects on seed-borne fungi, germination, emergence, and yield. A. Hermansen, G. Brodal, and G. Balvoll. 2000. Seed Science and Technology 27: 599 – 613
- Hot water treatment of vegetable seed: an alternative seed treatment method to control seed-borne pathogens in organic farming. E. Nega, R. Ulrich, S. Werner, M. Jahn. 2003. Journal of Plant Disease Protection 10:220-234.
- Suppression of Fusarium colonization of cotton roots and Fusarium wilt by seed treatments with Gliocladium virens and Bacillus subtilis. J. Zhang, C.R. Howell, J.L. Starr. 1996. Biocontrol Science Technology 6: 175-187.
Organic Seed Enhancement Companies
Germain's Technology Group North America
http://www.germains.com (verified 23 Mar 2023)
INCOTEC - Integrated Coating and Seed Technology, Inc.
http://www.incotec.com (verified 23 Mar 2023)
Kamterter II
https://www.kamterter.com/ (verified 23 Mar 2023)
