Postemergence herbicide application season is already upon us in much of Iowa, but with the delayed crop planting in some areas, it may extend through much of the month of June. Herbicide application timing should always focus on the sizes of weeds targeted but remember that many products use crop growth stage and calendar date as application restrictions.
This spring's weather has resulted in an unusually slow start to the growing season, especially when compared with the past two years. In springs like these, field operations are condensed and there may be temptation to skip some of the field preparation to get acres planted in a timely manner. This article will address considerations for herbicide applications in these situations.
This week is a welcome break from the fall chill, and it is a great opportunity to finish up any final fall weed management in pastures and no-till crop fields. Ideally, herbicide applications should be made when the sun is shining and daytime temperatures are above 50-55 degrees Fahrenheit. With high temperatures this week in the upper 60s and low 70s across much of the state, it’s a great time to complete this work.
Although most crop fields have not reached the stage for regularly planned POST herbicide applications, there likely are situations where people would like to get weeds controlled prior to the rain forecast later this week. The question is what impact will this weekend’s frost have on herbicide performance.
In response to problems with off-target movement and injury associated with dicamba applications on dicamba-resistant (Xtend) soybean, the EPA made significant changes to labels of the new dicamba products. While much of the discussion has focused on the Restricted Use designation and the requirement for applicators to receive dicamba-specific training, the EPA also clarified how downwind buffers and protections of susceptible crops are to be implemented.
The EPA recently announced changes to the new dicamba labels in response to widespread off-target plant injury in 2017. The most significant change is classification of the new dicamba formulations as Restricted Use Products. Other changes will reduce the hours available to spray soybean, including 1) restricting applications to between sunrise and sunset, and 2) reducing the maximum wind speed during application from 15 mph to 10 mph. The ability to cover all acres in a timely manner has always been an issue and these new limits will add to that difficulty.
Postemergence herbicides dominate the soybean market and are an important component of weed management systems in corn. One advantage of postemergence herbicides over soil-applied products is that the chemicals are applied directly to the target, thus avoiding interactions between the herbicide and soil. Direct application to the target somewhat reduces variability in herbicide performance; however, there are still several factors which influence movement of the herbicide into the target.
Apply when weeds are actively growing is a common statement found on labels of postemergence herbicides. While intended to help users obtain consistent results, these statements provide little guidance since post products are inherently applied while plants are actively growing (it is the growing season, after all). In spite of a large volume of research conducted to determine the effect of environmental conditions on herbicide effectiveness, we still have limited understanding of how weather and other factors influence a weed's susceptibility to
The loss of effective postemergence options for waterhemp due to herbicide resistance has led to resurgence in the use of preemergence (PRE) herbicides in soybean. Waterhemp’s extended emergence pattern requires that PRE herbicides remain at an toxic concentration later in the season than required for other weeds to provide effective control.
The adoption of herbicide resistant crops (e.g. Roundup Ready and Liberty Link) has increased the interest in preharvest herbicide applications since these crops allow the application of broad-spectrum herbicides late in the season with minimal risk of crop injury. While late-season applications have little impact on crop yields since the majority of competition between the crops and weeds has already occurred, herbicide applications at this time may improve harvest efficiency. Growers also use these treatments in an attempt to reduce weed seed production and th
