With mother nature making it appear as if winter is still present in early April, should herbicide programs be changed this spring? And what has occurred to any herbicides that were applied prior to the current cold temperatures and snowfall accumulations sweeping across the middle of the country?
Soil temperature and planting
Good news. Now is not the time to panic and second guess all previous decisions regarding your weed management plan. According to my soil thermometer where I’m located in Nebraska, the temperature at 4” depth is 37 degrees Fahrenheit this morning. This is quite a distance from the required average of 50 degrees Fahrenheit for corn to grow normally. For soybeans the soil temperature needs to push even higher to 60 degrees Fahrenheit.
In Nebraska, growers begin planting corn April 10th to 20th. In an average year Nebraska soils have been warmed to the needed temperatures by April 15th. With forecasts across the middle of the country calling for just a few days of warm weather followed by a dip back down into freezing, there may be a low probability of soils attaining adequate temperatures for corn or soybean planting by their usual dates.
Does cold weather affect herbicides that have been applied?
Any herbicides that were applied this spring will still be present when temperatures increase to allow plant growth. However, glyphosate efficacy could be decreased with the cold weather. Glyphosate will take a longer period of time to show that the target weeds have been controlled when cold conditions exist.
Residual herbicides already applied should not be affected unless they remain exposed on a dry surface. Most areas have received adequate moisture to incorporate the herbicide into the topsoil. Adhere to label guidelines for planting delays required where herbicides were used as a burndown or pre-emerge application. Days do not count if air temperatures are below 50 degrees Fahrenheit.
Do you need to adjust your herbicide program?
Stay with your current weed management program at this time. Remember that weeds are not actively growing at these low temperatures, either. Adjusting a herbicide program now could increase its cost without any benefit of increased weed control. Weed size, temperature and weather events will dictate if a change is needed. And our data shows us that an early planting date doesn't ensure the success of the crop. Even if it’s cold now, the calendar still shows that we have ample time for warm weather to move in so we can get the 2018 crops planted on a timely basis this year.