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Permalink What herbicides are appropriate for organic small grains?

Answer: Biological and allowed synthetic substances can be used for weed control, but there must be evidence that the first- and second-tier strategies are already in place, as defined by the National Organic Program. Currently, most organic small grains producers do not use organic herbicides for field-scale weed control. However, these substances may have some application for weed control in localized areas such as along fence lines, on ditch banks, or in limited weed patches. As with any new purchased input, check with your certifier prior to using the substance.

All organic herbicides are very limited in their effectiveness. These substances are non-selective and kill only the portion of the plant they contact directly. Because they do not kill the entire plant, repeated treatments will be necessary to use up the energy reserves in the roots as the weeds re-sprout. Because they are non-selective and will also injure the cash crop, organic herbicides should not be used as a method of in-crop weed control.

Low-toxicity herbicides are available from several suppliers. Scythe, produced by Dow AgroSciences, is made from fatty acids. Scythe acts fast as a broad-spectrum herbicide, and results can often be seen in as little as five minutes. It is used as a post-emergent herbicide sprayed directly on the foliage. It has no residual activity and is not effective on non-green, woody portions of plants.

Vinegar is an ingredient in several organic herbicides. One example, Burnout II, is a post-emergent herbicide that is sprayed onto the plant to burn off top growth, but is not guaranteed to kill the entire plant. The label on Burnout II states that perennials may regenerate after a single application and require additional treatment. Burnout II is 23% acetic acid. In contrast, household vinegar is about 5% acetic acid. Vinegar is corrosive to metal sprayer parts—the higher the acidity, the more corrosive. Plastic equipment is recommended for applying vinegar.

AllDown is another organic herbicide containing acetic acid. It also contains citric acid, garlic, and yucca extract. One brief California study compared the effectiveness of several organic herbicides to Roundup Pro. In this instance, AllDown provided the best control of broadleaf weeds after Roundup. While Roundup controlled 100% of the broadleaf weeds, AllDown had about an 80% control rate. However, this same study estimated the cost of Roundup Pro at $81 per acre, while the cost of AllDown was $1,733 per acre. Regardless of its effectiveness, the cost of AllDown would be prohibitive except on the most difficult weed patches.

Learn more in the ATTRA publication Weed Management in Organic Small Grains. This publication introduces the multifaceted, comprehensive strategy of weed management used for organic small grain production, combining techniques including crop rotation, sanitation, cultural practices, variety and seed selection and planting, cover crops, tillage, use of organic herbicides, and others.

Mention of specific products is for educational purposes only and does not constitute endorsement by NCAT, ATTRA, or USDA.

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