Investigate alternative weed controllers, such as vinegar, boiling water or mulch. Round-up in testing toxicity, has the LD 50 rating of tablesalt. On the Roundup ® For Lawns bottle, you’ll find even more info on the best way to treat each specific weed and comprehensive step-by-step instructions. Therefore, applying it any time the weeds are stressed, such as on a hot afternoon, will not be too effective. no wind leaves are dry temperature less than 90f silty or dirty water may neutralize its effect. I am not promoting round-up but I dislike misinformation. Thus, it is best to apply it once dew has completely gone. ... It’s Roundup WeatherMax at a quart with a 5 a.m. application providing 16 percent control and an 11 a.m. application providing 56 percent control. When Best To Use Roundup weed killer to Kill Weeds. At dusk, the growth of plants slows down and buckles up when the sun rises. The chemical has to be absorbed into the plant to be effective. To ensure success, spray the weeds' leaves until they're completely wet, but not dripping. Pesticides are carcinogens and neurotoxins and do not belong where other living things are. We expected that for Liberty – it is well known that you should spray Liberty in the heat of the day because it needs the heat to activate it as a contact herbicide.” He notes, “I was surprised that Roundup had a strong time-of-day effect. Don't apply herbicides around midday or early afternoon in summer. The best time of day to spray weed killer is NEVER! Roundup is a nonselective weed killer, usually applied to the foliage of weeds and other unwanted plants. Spray away When used as directed, Roundup ® For Lawns kills weeds without harming your lawn. Early morning and late afternoon are the best times for applying systemic herbicides in summer in warm climates, such as U.S. Department of Agriculture plant hardiness zone 9 and higher. For canola, Liberty and Roundup (Vantage Plus Max II) usually performed best at midday and worst in the early morning. Roundup Weedkiller is the Worlds best selling herbicide, used in gardens everywhere. This is the most resistant population of glyphosate-resistant Palmer amaranth I … Early morning dew could cause Roundup to run off. Roundup works best when you apply it in the afternoon, midday, or late morning in cold or cool climates. When is the best time of day to spray Roundup? Points To Remember Regarding The Best Time To Apply Roundup Roundup is a weed killer that kills the root of the plant so that weeds never come back. Time of day, per se, is not important. Herbicides: Time of day you spray can make a difference.