b'Timing CanBe EverythingSuccessful weed control with using a combination of tank mix chemistry and timing of applications. BY: ROSALIE I. TENNISONCONTROLLING A WIDE variety of weeds in a field can be a little like playingFor scenarios one and two, growers are recommended to blend soil-active the lottery. If you time it right, choose the best products and dont experi- herbicides into the soil along with irrigation, if possible. Otherwise, they ence any adverse environmental factors, you may have a winning combination. should time the application so rainfall can absorb the herbicides. Some her-To gamble with better odds of success for weed control and reduce thebicides may be labelled for application through overhead irrigation systems. chance of developing herbicide resistant weed populations, its recommendedAlthough some herbicides can be mechanically incorporated, Hutchinson says you use a tank mix of products registered for their combined success on theto do this only if irrigation or rainfall dont happen.weed spectrum in each fieldthen apply the combination at the right time. According to private consultant, Darin Gibson of Gaia Consulting in Newton, Timing is everything for successful weed control, says University of IdahoMan., Hutchinsons recommendations are sound, but Canadian growers may researcher Pamela Hutchinson. There really is no one size fits all approachnot be able to fully use them. He says potato producers in this country are wise when it comes to choosing tank mixes and application timing. when it comes to choosing tank mixes and application windows and believes The way growers want to do things doesnt always work at the same timethey can choose the most useful of Hutchinsons recommendations to use.and place, especially when weeds in one field are different than the weeds inGibson believes the best weed control scenario, based on Hutchinsons another, Hutchinson, a potato cropping systems weed scientist, says. As arecommendations, is the first. Hilling at planting and then applying herbicides result, some growers say their herbicide isnt working, but it could be theirimmediately is becoming more common in Canada, he says. The window for timing or their choice of products. herbicide applications are quite small, making timing and tank mix choices Hutchinson has developed a table growers can use to determine the besteven more critical.mixes for their weed spectrum in each of their fields. It also provides infor- We can use glyphosate as a broadcast application after weed emer-mation about application timing allowed by the herbicide labels and includesgence but before ground crack to control weeds, Gibson explains. However, herbicides labelled in both Canada and the United States. Growers should onlyGramoxone (Paraquat) is no longer available in Canada so that limits burn-off use recommended weed control products and tank mixtures labelled for theiroptions. Most Canadian growers do not use the drag-off production practice, countrys potato growing regions, Hutchinson says. so that also limits some of the options.Hutchinson has developed three scenarios for application timing of tankHutchinson cautions growers against unregistered uses but believes there mixes, but says not all would be useful in Canada: are still many options. I considered all the herbicides labelled for potatoes, 1. Hill followed immediately by herbicide application, either at the samebut some are only for pre- or post-emergence, she explains. I have found time as planting or as soon as possible after. Additional applications of herbi- that some of the best weed control in potatoes can be had by timing the right cides with foliar activity may be needed if weeds emerge after the initial spray.mix after planting potatoes and before they emerge.2. Hill later than planting but still before potato emergence. Hilling willUsing a herbicide immediately after planting is effective in controlling remove weeds which have come up since planting. As in the first scenario,some of the more troublesome weeds, and there is still opportunity to use apply herbicides immediately after hilling, before any more weeds emerge.a foliar if needed later in the season, Gibson says. Tank mixes are a good Additional applications of foliar active herbicides might be needed for weedsapproach to reduce resistance, but we have to use registered and company coming up later. supported combinations. We need to be careful. We can adapt Dr. Hutchinsons 3. Reduce weeds with a drag-off operation after planting, but beforesuggestions to our growing situation, but our season is shorter, and our prac-potato emergence. Hilling followed by herbicide application is not performedtices are a little different and may not allow for some of the options.until after potato emergence. Drag-off is used only in a few production areasHutchinson says the table of options she developed is extensive and shows in the U.S. and rarely in Canada. growers how to target the weed spectrum in each field with the best tank 18 SPUDSMART.COM SPRING 2020'