Senwes Scenario June/July 2018 - Page 15

AGRICULTURAL When continuously planting glyphosate resistant crops, the risk of developing glyphosate resistant weeds can be significantly reduced by using a variety of herbicides that control each weed species in your field and by adhering to certain guidelines. In doing so, you will be able to apply a specific course of action that suits the situation.  By Julias Ramohlabi Senwes Manager Developing Farmers P hosphonic acids are non- selective, broad spectrum, post-emergence, systemic her- bicides that are active on leaves and other green parts of plants. It works by disturbing various physiological and biological processes in the plant. The most important effect is that of inhibition of aromatic amino acid syn- thesis, which causes a chain reaction of inhibiting other synthesis processes in the plant. The most common symptoms of the phosphonic acids are termination of growth, chlorosis of the foliage, followed by necrosis. AN INNOVATIVE SOLUTION Glyphosate has provided a revolutionary means for providing broad spectrum weed control in maize, soybeans and other crops via insertion of a glyphosate resistant gene in the seed. Growers have widely embraced the technology, because it provides conve- nient, effective and economical weed con- trol in maize and soybeans. THE DOWN SIDE Research has shown that intensive and long-term exclusive use of glyphosate can lead to the development of glyphosate resistant weeds. MANAGING THE PROBLEM Integrated management practices can Widespread popularity and use of maize, soybeans and cotton with gly- Glyphosate (N-(phosphonomethyl) glycine) is a broad-spectrum systemic herbicide used to kill weeds, especially perennials. It is typically sprayed and absorbed through the leaves of the plant. Initially patented and sold by Monsanto Company in the 1970’s under the trade name Roundup, its U.S. patent expired in 2000. phosate resistance makes it important By engineering and inserting a glypho­ for preventing and managing the vars such as soybean, maize and cotton, to adhere to the following guidelines sate resistant gene in the seed of culti- resistance of weeds to herbicides. these cultivars greatly improve conven- minimise this risk, whilst providing growers with a more consistent and effective weed control programme. Until now, most instances of weed resistance to glyphosate have occurred when glyphosate is used continuously and almost exclusively for ten or more years in orchard and vineyard crops, no-till (a sys- tem of crop production in which the soil is disturbed as little as possible) burn down and continuous planting of glyphosate resistant soybean and soybean-cotton rotations. It is expected that many farmers will choose to plant continuous glyphosate resistant maize, soybeans and cotton in the future. This practice can be effective- ly and profitably utilised – but important guidelines must be brought into account. While the odds of developing glypho- sate resistant weeds on your farm are probably less than with most other her- bicides, weed resistance is nevertheless developing because of heavy reliance on glyphosate. Producers should bear in mind that the fact that they are planting seed with a glyphosate resistant gene does not mean that glyphosate is the only herbicide that may be used on the crop. tional farmers' ability to control weeds, since glyphosate can be sprayed on fields without dama­ging the crop. FACTORS THAT AFFECT EFFICACY OF GLYPHOSATE Glyphosate requires actively growing green plant tissue to function. Application to drought-stressed weeds or weeds with little green foliage; weeds covered with dust; weeds damaged by insects or disea­ ses may result in reduced weed control. Heavy rainfall or irrigation shortly after application may require retreatment. Tillage or mowing within 3 days following application may reduce weed control. It is not advisable to spray glyphosate if conditions of thermal inversion exist, or if wind direction and speed may cause spray to drift onto adjacent-non target areas. REFERENCES Basic weed science and principles of chemical weed control by AVCASA From Perdue University Extension bulle- tin: facts about Glyphosate-resistant weeds, Boerbom and Owen, Dec 2006 http://www2.dupont.com/production agriculture /en US/products services/ herbicides SENWES SCENARIO | WINTER 2018 13