Volume 38, Number 13 | JULY/AUGUST 2012
$4.25
PRACTICAL PRODUCTION TIPS FOR THE PRAIRIE FARMER
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Timing critical for fall herbicide application Choosing the right application window for pre- and post-harvest weed control can be a guessing game. Follow this guide to fall application timing and cool-weather spraying BY ANGELA LOVELL
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s fall progresses, postharvest herbicide application becomes a bit trickier. Effectiveness will be influenced by factors such as temperature, target weeds, the amount of frost damage and the products being used. Timing is critical. “One of the primary challenges with a post-harvest herbicide application is whether you are going to have enough time for regrowth after harvest,” says Clark Brenzil, provincial weed specialist with the Saskatchewan Ministry of Agriculture. This is especially crucial when dealing with perennial weeds. “You want to make sure you have four to six weeks after harvest of open weather with warm growing conditions for that plant to get enough growth on it so you have a target again for application and before you get a killing frost.”
PERENNIAL WEEDS Perennials weeds such as quackgrass and foxtail barley are best controlled pre-harvest in early fall when they are still actively growing. But they can be controlled post harvest as long as there is enough regrowth to make the product effective.
“When herbicide is applied on perennial plants in the fall it goes into the root system along with the food material that is being transferred for storage by the plants for the winter, so it is a much more effective way of controlling weeds than applying it in the spring,” says Nasir Shaikh, Manitoba Agriculture, Food and Rural Initiatives’ provincial weed specialist. Weeds such as Canada thistle can provide more of a challenge because they generally have poor regrowth after harvest. Dandelions, on the other hand, may grow more actively in cool fall conditions than in hot, dry weather. The odds of having good plant tissue remaining that is warm and pliable enough for the herbicide to be effective drops dramatically past the end of September. “If you are doing perennial weed control with glyphosate or any Group 2s you want to apply the product by the first week of October, and that’s only if conditions are still reasonably warm at that time,” says Brenzil. Hitting this small window of opportunity becomes harder the further north you go, where harvests can be late and frosts early. This is why Brenzil recommends that farmers in northern areas focus more on pre-harvest rather than post-harvest applications for perennial weed control.
PHOTOS: ANGELA LOVELL
It can be challenging to control Canada thistle late in the season, as they generally have poor regrowth after harvest. Consistently dry, warm and sunny days both before and after application are needed, especially with herbicides such as glyphosate or Group 2s, to allow the maximum amount of product to move within the plants to the target. “Leaves are often not the target,” says Brenzil. “The leaves are just the receptor. The target is the buds and growing points that the plant is laying down for winter for growth next spring.”
Under cooler conditions, particularly in the case of glyphosate, active ingredients can get bound up in the leaves, which will give good die off in the top growth but poor long-term weed control. “Biological activity basically stops once you get below 4 or 5 C, so if you have evening temperatures that are dipping down below that and your daytime peaks are less than about 15 C then you probably should not be spraying,” says Brenzil.
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FROST TOLERANCE Quickly changing weather conditions can affect the ability of weeds to acclimatize to colder conditions and tolerate a frost. “If it’s really warm and then all of a sudden you get minus two or minus three nights you can get more damage to the plant than if temperatures make a gradual ongoing procession down to reasonably cold overnight condi-
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Wheat & Chaff ..................
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Features ............................
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Columns ........................... 10 Best of Grainews ............. 16 Cattleman’s Corner .......... 25 Machinery & Shop ............ 30
Variable rate herbicide application T:10.25” LISA GUENTHER PAGE 7
COULDA
SHOULDA
WOULDA
MF production returns to the U.S.
SCOTT GARVEY PAGE 30
FarmLife ............................ 36 Crop Advisor’s Casebook
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DID PROSARO T:3”
Visit us online for Demonstration Strip Trial (DST) results at BayerCropScience.ca/ ItPaystoSpray BayerCropScience.ca/Prosaro or 1 888-283-6847 or contact your Bayer CropScience representative. Always read and follow label directions. Prosaro® is a registered trademark of Bayer. Bayer CropScience is a member of CropLife Canada.
C-53-06/12-BCS12009-E