This blog reviews the latest products, plants and innovations in gardening. It also provides a link for my many gardening friends who are members of the GardenMessenger and Seedmessenger Yahoo groups and their sub-groups that I moderate.

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Location: Australia

I am a semi-retired UK botanical garden curator and former international horticultural consultant, who has worked extensively in Europe, the Middle East, North America and Australia. I spend part of the year in Australia and part in Europe, mainly due to family and work commitments. I earn my living from writing and editing Internet copy, articles and books. I have written over fifty books on gardening and have been translated into twenty-four different languages. I am a former UK Garden Writer of the Year and a previous Quill & Trowel Award Winner from the Garden Writer’s Association of America. I am interested in developing gardening communities on the Internet and I manage the popular GardenMessenger Yahoo group, along with its various sub-groups like PondMessenger and SeedMessenger. I also edit International Water Gardener and its associated regional web-sites.

Friday, September 29, 2006

Glyphosate Resistant Weeds?

Horseweed - Conyza canadensis

Two rapid, non-destructive tests have been developed by the United States Agricultural Research Service to test the effectiveness of glyphosate (the active ingredient in Round-up) on weeds that it is suspected are developing a resistance to the herbicide. In 2000, Horseweed, Conyza canadensis, became the first weed species to develop resistance to glyphosate in cropland where glyphosate-resistant soyabeans were grown. Glyphosate-resistant biotypes of Horseweed have now been confirmed in 13 states east of the Mississippi River. Glyphosate is effective at killing all plant types including grasses, broad-leafed weeds and sedges, as well as perennial and woody plants. After emergence, glyphosate-resistant crops are capable of tolerating multiple applications of the herbicide, while weeds are killed. However, repeated use over many years has left several weed species resistant to glyphosate. The two tests can be used together.

One method, which involves dipping a whole leaf into a glyphosate-based mixture and looking for signs of injury, is quick and easy to perform. To achieve double confirmation of the weed's status, a second assay can be used. This method takes advantage of glyphosate's mode of action, which involves inhibiting amino acid metabolism in what is known as the shikimic acid pathway. Leaf tissue samples are removed, and amino acid levels are measured with specialised laboratory equipment. If glyphosate resistance is confirmed, the tests should help reduce the spread of resistant Horseweed populations because growers will use different herbicides to manage the resistant weeds. While this research is directed at commercial growers, it is very relevant to home gardeners as weeds do not respect field or garden boundaries.

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