Page 1 Page 2 Page 3 Page 4 Page 5 Page 6 Page 7 Page 8 Page 9 Page 10 Page 11 Page 12 Page 13 Page 14 Page 15 Page 16 Page 17 Page 18 Page 19 Page 20 Page 21 Page 22 Page 23 Page 24 Page 25 Page 26 Page 27 Page 28 Page 29 Page 30 Page 31 Page 32 Page 33 Page 34 Page 35 Page 36 Page 37 Page 38 Page 39 Page 40 Page 41 Page 42 Page 43 Page 44 Page 45 Page 46 Page 47 Page 48 Page 49 Page 50 Page 51 Page 52 Page 53 Page 54 Page 55 Page 56 Page 57 Page 58 Page 59 Page 60 Page 61 Page 62 Page 63 Page 64 Page 65 Page 66 Page 67 Page 68 Page 69 Page 70 Page 71 Page 72 Page 73 Page 74 Page 75 Page 76 Page 77 Page 78 Page 79 Page 80 Page 81 Page 82 Page 83 Page 84 Page 85 Page 86 Page 87 Page 88 Page 89 Page 90 Page 91 Page 92 Page 93 Page 94 Page 95 Page 96 Page 97 Page 98 Page 99 Page 100 Page 101 Page 102 Page 103 Page 104 Page 105 Page 106 Page 107 Page 108 Page 109 Page 110 Page 111 Page 112 Page 113 Page 114 Page 115 Page 116Herbicide Efficacy THOUGH herbicides are marketed as the “kill it dead” silver bullets to all kinds of weed problems, some herbicides’ efficacy actually varies quite significantly depending on conditions at spraying time. Because GPS guidance now allows farmers to spray day or night, Farming Smarter lead a three-year study to determine if and when the time of day a herbicide is applied would affect its resulting efficacy. The results surprised even the Farming Smarter team: not only does timing make an impact on herbicide efficacy in many crops, some of farmers’ more commonly-held beliefs about spray application timing are not entirely correct. “The time of day that herbicide is applied does impact its efficacy more than I ever expected,” says Ken Coles, general manager of Farming Smarter. “But it’s not as easy as just saying: ‘You should spray at this time of day’ or: ‘You should never spray at this time of day’. I can’t tell you the best time of day because the weather is always different. But there are some general guidelines that we determined from the study.” One of the most commonly held rules-of-thumb about spray- ing is that very early morning applications are best. While it is true wind is usually at its calmest just as the sun starts to rise, it turns out that glyphosate efficacy, especially for pre-season burn- down, is also at its lowest. New Research Shows Herbicide Application Timing Influences its Efficacy A new study by Farming Smarter proves the time of day a herbicide is applied matters, especially in crops with heavy disease pressure and/or herbicide resistance issues. “When you are doing a pre-seed application, the weather tends to be quite cool. Nights drop to less than five degrees; plants are stressed and stop actively up-taking and translocat- ing,” says Coles. “We found that very early applications tended to be the least effective. This doesn’t mean glyphosate can’t work first thing in the morning, but when you are looking for the probability of optimum success, it’s not first thing in the morn- ing. So I say sleep in. Don’t wake at the crack of dawn.” In summer, many farmers opt to apply an in-crop herbicide in the late afternoon, thinking the heat of the day is past so plants will be more able to absorb the chemical. Wrong again, accord- ing to the Farming Smarter study. Even once the thermometer dips towards evening, the long hours of heat stress earlier in the day continue to affect a plant’s ability to take in herbicide. While the decrease in glyphosate’s efficacy is not quite as dramatic as is seen in cold-stressed plants at pre-seed timing, there remains visibly reduced efficacy in heat-stressed plants. “What we found is that the duration that a plant is under stress really affects how well the herbicide works. For the purposes of the study, researchers applied herbicide at 5 a.m., noon and midnight at multiple times throughout the growing season. This year, Coles followed up on the efficacy study with a demonstration plot in which he sprayed mid-summer 40 www.seed.ab.ca | Advancing Seed in Alberta Farming Smarter’s field school results showed fairly good response for many of the 2 p.m. applications, even in cases where the application occurred when the temperature was 27 C or more. Photos: Farming Smarter