Agroworld

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
mustards	122 F	20 min
collards	122 F	20 min
turnip	122 F	20 min
cabbage	122 F	25 min
cauliflower	122 F	20 min
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 Treatment of Vegetable Seeds to Eradicate Bacterial Plant Pathogens in Organic Production Systems (Miller and Ivey, 2005).

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)

1. Cover Cropping / Green Manure: In our State of the World 2011 report, agroecologist and author Roland Bunch defines cover crops / green manure as “any plant, whether a tree, bush, or vine, that is used by a farmer to…improve soil fertility or control weeds.” In practice, cover crops are planted alongside or interspersed with other crops to cut soil-eroding wind, prevent overexposure to the sun, and stimulate a healthy soil system. Just as farmers will turn to manure to bolster the soil, they can also clip and spread cover crops’ leaves as organic green manure.
Cover Cropping / Green Manure in Action: According to Roland Bunch, there are more than a million farmers now actively using cover crops / green manure worldwide. In Africa alone, there are over 120 plant species that are being used or could be used for this purpose. One promising example is the cowpea (also known as the black-eyed pea). This legume is both a nitrogen-fixer, which means that it takes nitrogen from the air and replenishes it in the soil, and deeply rooted, which makes it resistant to drought. Furthermore, the cowpea itself is a nutritious staple food for both people and animals.

2. Microdosing Fertilizer: According to the International Crops Research Institute for the Semi-Arid Tropics (ICRISAT), microdosing is defined as “the application of small, affordable quantities of fertilizer with the seed at planting time or as top dressing 3 to 4 weeks after emergence.” This precise process stands in stark contrast with the field-wide fertilization used by many farmers. Fertilizers are often very expensive for farmers in the developing world, particularly in sub-Saharan Africa. Microdosing can help reduce fertilizer costs, while also targeting the seeds farmers want to cultivate.