Monday, September 22, 2014

A History Of Treating Wheat Seed

Some of the biggest success stories in plant disease control involve the use of seed treatments, particularly of small grain cereals, e.g., wheat, barley, and oats. These seed treatments are composed of fungicides that have a variety of chemistries. They generally are low in toxicity to plant and animal life, and because they are applied in low doses, they have little environmental impact. In some cases these doses are as low as 1 g of active ingredient per hectare (0.4 g per acre). As a result of these low doses, the cost per hectare to a grower tends to be fairly low, usually less than $5 per hectare and often less than $2.50 per hectare ($1/acre). Regardless of the yield potential of the planted crop, application of seed treatment is one of the least expensive choices a grower can make. Often, growers who farm in areas of low productivity may be tempted to forgo application of a seed treatment. This is usually a mistake since it is these very growers who cannot afford any yield or quality losses due to a plant disease.
Another major impact that seed treatments have had on the small grain industry is their effect on plant breeding. In the early part of the 20th Century, many wheat breeders spent a considerable portion of their effort on breeding for resistance to common bunt. Today, with this disease controllable with seed treatment they are able to spend their efforts on breeding for other attributes, i.e. grain quality.
This lesson will introduce you to the history of small grain seed treatments, the diseases they are capable of controlling, the various chemistries used, and their mode of action.

Historical Aspects

The history of seed treatment goes back over 300 years (1, 8). In 1670 a ship carrying wheat grain went down off the coast of England near the city of Bristol. Evidently, the ship was close enough to shore that nearby farmers were able to retrieve some of the grain. Having been soaked in sea water, the grain was not fit for processing into flour, but some farmers planted it. The crop that resulted was remarkably free of "smut", whereas most of the fields planted with grain that had not been soaked in seawater showed heavy smut infestation.  ( I bet it goes back to Biblical times but have not looked for evidence.)
Over the next 100 years, various people tried treating wheat seed with salt, lye, urine, etc. to see if they could reduce the amount of smut that developed. Use of a salt/brine mixture was known in various parts of Europe. The French botanist Tillet published an article on this in 1770 indicating that treating seed with such materials would reduce the amount of smut. In 1807, the Swiss scientist Prevost showed that treating smut spores with a liquid solution of copper sulfate inhibited their germination. Over the next 100 years, recommendations were issued to treat wheat seed with copper sulfate to reduce the infection with common bunt. However, this compound is a general biocide and much injury to seed germination was noted. In 1895, the use of formaldehyde was suggested by the Germans. It gained in popularity due to its effectiveness and low cost but certainly was not pleasant nor safe to use for the person treating the seed.
In 1912, organic mercury compounds were tried in Germany and found to be quite effective in controlling common bunt. However, initially they were too expensive to use and also had to be applied as a liquid that left the grain too wet to use without drying. By 1917, research on other compounds showed that copper carbonate was safer to use than copper sulfate and could be applied as a dry powder formulation. This treatment was first used in Australia and was soon adopted in the United States. However, one disadvantage of the dry treatment was the dust problem that developed put the person treating the seed at risk. This soon led to tests with "slurries", whereby the dust formulation was mixed with a small amount of water and added to the seed. This helped increase the "coverage" of the seed without wetting it too much.

Thankfully, we have come a long way in the development of seed treatments available to farmers and seedsmen this fall.

Ed Winkle

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