"If I had RUP dicamba training in 2018, do I need training in 2019?" The answer to that question, which is "Yes," and other questions about training and new application requirements for the three RUP dicamba products are covered in this FAQ.
Pollen-mediated gene flow at a distance could allow the spread of rare herbicide-resistant alleles and favor the evolution of multiple herbicide-resistant biotypes through the accumulation of different resistant genes in an individual weed or weed population. From the Nebraska Crop Management Conference Proceedings.
For successful marestail management in the fall, apply herbicides after harvest while weather conditions remain favorable (air temperature above 50°F). Effective control now may negate the need for an early spring burndown application.