Template:Chapters 7.6

7.6 - Vinegar, bleach and saltwater treatment of seeds

Vinegar, Nick Moroz, University of Guelph, Canada

Suggested citation for this chapter.

Author name (2022) title of chapter. In Farmpedia, The Encyclopedia for Small Scale Farmers. Editor, M.N. Raizada, University of Guelph, Canada. http://www.farmpedia.org

Introduction to seed treatment as a preventative measure

Options for reducing seed-borne pathogens in organic agriculture are limited to physical heat treatments and certain organic treatments, as synthetic pesticide protections cannot be used (Van der Wolf, Birnbaum, & Van der Zouwen, 2008). Saltwater and vinegar seed treatments represent organic options, while bleach is an synthetic compound that sterilizes seeds and can subsequently be washed off. Disinfecting seeds prior to sprouting helps prevents the possibility of plant disease epidemics by killing disease-causing organisms living within or on the surface of the seed (Munkvold, 2009). Preventative measures can decrease the probability of contamination in a field and reduce the use of pesticides to control plant epidemics that could have, with hindsight, been controlled through seed treatment.

Seed disinfection can kill seed-borne pathogens, or external pathogens living on the seed surface, while also protecting the seed, depending on the type of seed treatment (Munkvold, 2009; RPD, 1992). In addition to killing plant-pathogens, seed treatments can protect seedlings from common soil-inhabiting fungi that cause seed-rots (Munkvold, 2009; RPD, 1992). Finally, an effective seed treatment can reduce the need for multiple field applications of fungicides or bactericides later in the growing season (Mancini & Romanazzi, 2014). Aggravated use of pesticides is damaging to the local environment, economically costly, and posits a health hazard to farmers using these applications without respirators or advanced safety equipment. Subsistence farmers interested in minimizing pesticide use and improving crop health can use the preventative disinfection measures as outlined in this chapter. Within this encyclopedia, chapters on “Pesticide Seed Applications” provide more information on effective seed treatment technologies.

Solutions for Seed Disinfection: Bleach, Vinegar, & Saltwater

Bleach

Sodium Hypochlorite, or commercial liquid laundry bleach, is a common choice for surface sterilization and it is readily available in many places. It can be diluted to proper concentrations needed for seed disinfestation from its original concentration of 5.25%-5.45% sodium hypochlorite (RPD, 1992). Seeds can be sterilized by immersion in a solution of 1 part bleach (~5.25% sodium hypochlorite) and 3 parts of water, for about two minutes (RPD, 1992), or 0.5% - 1.0% sodium hypochlorite for 10 minutes. This procedure works best when seeds are shaken periodically in the solution and then rinsed with water at least twice (Sauer & Burroughs, 1986). The time period and concentration may have to be adjusted for certain varieties, as optimal sterilization conditions that still allow for good seed germination can be different between seeds (Sweet & Bolton, 1979).

Bleach can be used for protection against fungus, and other clearing solutions have been used against viruses. Bleach soaks can also free seeds from root rot fungus and Fusarium wilt (RPD, 1992). Using a fine mesh or stringing bag, continuously agitate seeds for 40 minutes using 1 pint of liquid household bleach to 8 pints of water, and for each pound of seed treated, use 1 gallon (~3.78 Liters) of solution (RPD, 1992). Finally, use of the alkaline cleaning solid trisodium phosphate in solution can eliminate or reduce transmission of tobacco mosaic virus in pepper and tomato seeds (RPD, 1992).

After treating multiple different species’ seeds with multiple different chemical seed treatments, Sweet and Bolton (1979) came to the conclusion that a 0.5% solution of calcium hypochlorite may be the most effective seed-sterilization agent when applied for 10 minutes. Calcium hypochlorite is known as chlorine powder or bleaching powder and is used in many water-treating activities and as a bleaching agent. Sweet and Bolton (1979) found that this solution was the least detrimental to the emerging seedlings while being easily prepared, safely handled, and convenient to store. Following application of bleach, seeds should be thoroughly rinsed with water, with three subsequent washes with water shown to be most effective (Sweet & Bolton, 1979).>/p>

Sweet and Bolton (1979) also studied seed germination levels following each treatment and found that greater concentrations than 0.5% solution calcium hypochlorite and longer contact times reduced seed germination and did not improve the decontamination levels (Sweet & Bolton, 1979). They concluded that if seeds cannot be decontaminated with hypochlorite, than efforts could be shifted to find more effective seeds rather than a better sterilizer (Sweet & Bolton, 1979).

Vinegar

Since the development of synthetic pesticides, pesticide seed treatments have been used almost exclusively to control seed-borne pathogens (Borgen & Nielsen, 2001). Now, many alternative seed-disinfectants are being sought for heightened cost-effectiveness, accessibility, and to reduce the use of pesticides. One scientific study showed that some key organic acids, such as acetic acid (vinegar), at concentrations of 2.5% or higher reduce seed-associated bacteria (Van der Wolf et al., 2008). The researchers also showed that only organic acid to reduce seed germination at this concentration was propionic acid (Van der Wolf et al., 2008). In another study, researchers conducted trails in fields, disinfecting seeds with acetic acid, and found the treatments reduced common bunt (Tilletia tritici) in winter wheat by 91.5-96.2% without negatively effecting the seed germination (Borgen & Nielsen, 2001).

Vinegar is commonly considered to be useful as a sanitizing agent for household cleaning and home gardening due to its acidic nature, with potential for use by farmers who can access vinegar from fermented products. White distilled vinegar is considered as an eco-friendly organic fungicide and herbicide (Mancini, 2012). Thus, vinegar can be carefully applied to seeds in order to sterilize them. One method known for sterilization of seeds or beans is the immersion of dried seeds for 10 to 15 minutes into a bowl consisting of 1 tablespoon of apple cider vinegar to 1 quart of drinkable water (Mancini, 2012). Following immersion, a thorough rinsing of seeds for 5 minutes and subsequent drying prevents permanent seed damage from prolonged vinegar acidity (Mancini, 2012). Placing dry seeds in a netting bag with a tie and label simplifies this process (Mancini, 2012). Use of 1 tablespoon of white distilled vinegar in this process will have the same affect as the apple cider vinegar (Stouffer, 1999).

Sanitizing combinations of white distilled (or apple cider) vinegar with hydrogen peroxide, followed by subsequent washing with water, has also been shown to be an affective method for cleaning fruits and vegetables (Stouffer, 1999). It is considered to be ten times as effective as either solution alone (Stouffer, 1999). Use of clean sprayers filled separately with vinegar and hydrogen peroxide (never mixed) simplifies the cleaning process (Stouffer, 1999). Fruits and vegetables were sprayed first with vinegar, then immediately sprayed with hydrogen peroxide, shortly followed by a water rinse (Stouffer, 1999). The order of the vinegar or hydrogen peroxide application did not matter and neither is toxic in the small amounts remaining on washed products (Stouffer, 1999). Such methods could be applied to seed sterilization as affective bacterial killing agents on the seed surface. Finally, a recipe for preventing cross contamination of gardening tools is soaking tools in a half and half solution of white vinegar (50% vinegar and 50% water), which acts as a fungicide to kill any plant contaminants on these tools over a short time period (Martina, 2015).

Saltwater

Soaking in salt water is an effective disinfectant for seeds and is beneficial in the control of seed-borne fungi. One of the first seed-borne fungus discovered was Tilletia caries, which causes a covered smut of wheat, as described by Jethro Tull in 1733 (Kolotelo et al., 2001). Tull found that farmers whose wheat seed had been salvaged from the ocean was free of this smut, and this lead to the conclusion that salt water disinfected the wheat seed through its brining action (Kolotelo et al., 2001).

In high concentrations, salt water can act as an effective antimicrobial (Matsko, 2016). This is due to the cytolysis (cell reputing) of many bacterial cells that occurs due to the highly concentrated salt water. This is characteristic of hypertonic (high solute) solutions, and bacteria that are unable to live in such conditions. A sufficient method to create a salt-water disinfectant consists of the following steps. Add a teaspoon of salt into a clean cup of warm water and mix until all the salt is dissolved in the water (Matsko, 2016). Regular cooking salt will be effective (Matsko, 2016).

No one method may be perfectly effective as a disinfectant for any given seed variety

The most effective preventative measures to control seed-borne diseases are to only plant health seeds in the first place, preventing contamination, and to choose disease-resistant varieties (Borgen, 2004). However, in many situations it is often critical to reduce the degree of pathogen inoculum on seeds in order to prevent the infection of other plants and the spread of disease in fields (Kolotelo et al., 2001). There is a large micro-flora associated with seeds, but their effects on seeds are largely unknown (Kolotelo et al., 2001). Thus, it is safest to disinfect seeds as a reasonable preventative measure.

Attempts to attain seeds that are completely free from active bacteria and fungi usually results in failure because seed disinfectants are either too strong and damage the seed or are too weak to fully treat the seed (Wilson, 1915). Additionally, microbes located within the seeds are not released until germination (Sweet & Bolton, 1979). A more severe treatment will kill bacteria within the seed, but also cause more damage to the embryo (Sweet & Bolton, 1979). Some disinfectants are more effective than others, such as the three simple solutions outlined above. However, it should be recognized that no single surface disinfectant is perfect under every condition and each should be critically considered (Wilson, 1915; Sweet & Bolton, 1979).

Resources Moving Forward

Seed handling guidebook. Although this resource was meant for tree seeds, its outlines and applications are useful for all species’ seed treatments. Retrieved from: https://www.for.gov.bc.ca/hti/publications/misc/seed_handling_guidebook_hi.pdf

Natural crop protection applications for fighting pest and pathogens in the tropics: http://www.naturalcropprotection.margraf-verlag.de/overin.htm

Website full of organic treatments for seeds for the control of pests and pathogens in the tropics: http://www.oisat.org/control_methods/other_methods/seed_treatment.html

Research book on pesticide seed treatments: Gullino, M. L., & Munkvold, G. (Eds.). (2014). Global Perspectives on the Health of Seeds and Plant Propagation Material (Vol. 6). Springer.

References

1. Borgen, A., & Nielsen, B. (2001). Effect of seed treatment with acetic acid in control of seed borne diseases. In Proceedings of the BCPC Symposium No. 76:“Seed Treatment: Challenges & Opportunities” (Vol. 76). Farnham.

2. Borgen, A. (2004). Strategies for regulation of seed borne diseases in organic farming. Seed Testing International-ISTA News Bulletin, 127, 19-21.

3. Kolotelo, D., Steenis, E. V., Peterson, M., Bennett, R., Trotter, D., & Dennis, J. (2001). Seed handling guidebook. British Columbia Ministry of Forests, Tree Seed Centre.

4. Mancini, N. (2012). Controlling and Sterilizing Seeds. Organic gardening simplified. Retrieved from: http://www.organicgardeningsimplified.com/images/seeds/seeds.pdf

5. Mancini, V., & Romanazzi, G. (2014). Seed treatments to control seedborne fungal pathogens of vegetable crops. Pest management science, 70(6), 860-868.

6. Martina. (2015). Vinegar to keep your Garden Growing. Natural Clean. Retrieved from: http://naturally-clean.ca/vinegar-to-keep-your-garden-growing/

7. Matsko, C. M., Expert Reviewed. (2016). How to make a quick disinfectant for minor cuts and abrasions. Wikihow. Retrieved from: http://www.wikihow.com/Make-a-Quick-Disinfectant-for-Minor-Cuts-and-Abrasions

8. Munkvold, G. P. (2009). Seed pathology progress in academia and industry. Annual review of phytopathology, 47, 285-311.

9. Sauer, D. B., & Burroughs, R. (1986). Disinfection of seed surfaces with sodium hypochlorite. Phytopathology, 76(7), 745-749.

10. Stouffer, J. (1999). Vinegar and Hydrogen Peroxide as Disinfectants. Tau Topics. Retrieved from: http://www.michaelandjudystouffer.com/judy/articles/vinegar.htm

11. Sweet, H. C., & Bolton, W. E. (1979). The surface decontamination of seeds to produce axenic seedlings. American journal of botany, 692-698.

12. Report on Plant Disease (RPD) No. 915. (1992). Vegetable Seed Treatment. Department of Crop Sciences, University of Illinois at Urbana-Champaign.

13. Van der Wolf, J. M., Birnbaum, Y., Van der Zouwen, P. S., & Groot, S. P. C. (2008). Disinfection of vegetable seed by treatment with essential oils, organic acids and plant extracts. Seed science and technology, 36(1), 76-88.

14.Wilson, J. K. (1915). Calcium hypochlorite as a seed sterilizer. American journal of Botany, 2(8), 420-427.