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How can I treat external spores in organic grain?

Answer: The smut and bunt diseases can basically be broken into two groups. In the first group, fungal spores occur on the exterior of the seed coat. This group includes common bunt of wheat, covered smut in barley, and loose smut in oats. These spores on the coating of the grain infect the plant after seeding but before emergence. These diseases can be quite serious: common bunt can wipe out 60% to 70% of a crop.

However, because these spores are on the exterior of the seed, some organic treatments show promise. Organic producers in Europe have had success with a product called “Tillecur.” This is a commercially available treatment based on a formulation of mustard powder. Likewise, largescale equipment used to treat seed with steam jets is also used in Europe.

A beneficial fungus, Muscodor albus, has shown some promise in research trials. M. albus is an “endophytic fungus first isolated and described from the non-native cinnamon tree (Cinnamomum zeylanicum) in Honduras by Gary Strobel” at Montana State University (Biocontrol News and Information, 2008). When used as a fumigant, this fungus kills common bunt spores (Goates and Mercier, 2009).

The beneficial bacteria Bacillus subtilis is a possible organic seed treatment for these diseases. Bacillus subtilis can be used to control storage fungi such as Penicillium and Aspergillus (Grey, 2009). Bacillus subtilis is sold under the trade name Kodiak and is approved for organic crop production. For Kodiak label information, see ATTRA’s Biorationals: Ecological Pest Management Database.

For producers with small amounts of seed, washing may be an option. Wash seed in hot water and then dry before planting. Or, wash with a dilute solution of bleach in hot water for even greater efficacy. Take care with any heat treatment of seed because excessive temperatures can kill the seed and decrease the germination rate.

In 1888, the Danish seedsman J.L. Jensen proposed the following standards for hot water treatment of seeds. “Basically, this process involved soaking the seed for 110 minutes in water held at 118.4°F (48°C), or 95 minutes at 120.2°F (49°C)” (Mathre et al., 2006). Trial and error may be needed if using the hot water-wash method, as no recent standards are available for grains. Run a test batch of 100 kernels in various treatments and then test the germination of the seeds after the treatment.

While not specific to grain seeds, guidelines for using hot water wash for vegetable seeds are available from Ohio State University Extension, in Hot Water and Chlorine Treatment of Vegetable Seeds to Eradicate Bacterial Plant Pathogens.

The ATTRA publication Disease and Insect Management in Organic Small Grains will be a useful resource as you continue to explore this topic. The publication outlines various strategies that make up a good organic disease and insect management plan, and describes some specific diseases and insects that affect small grain crops.

References

Biocontrol News and Information. 2008. Endophyte Spices up Biofumigation. Vol. 28. No. 4. p. 69N–74N.

Goates, B. and J. Mercier. 2009. Effect of biofumigation with volatiles from Muscador albus on the viability of Tilettia spp. teliospores. Canadian Journal of Microbiology. Vol. 55. p. 203-206.

Grey, Dr. Bill. Montana State University. 2009. Personal communication with NCAT Agronomist Susan Tallman.

Mathre, D.E., R.H. Johnston, and W.E. Grey. 2006. Small Grain Cereal Seed Treatment. The Plant Health Instructor. DOI: 10.1094/PHI-I-2001-1008-01.