Wetter and cooler than normal weather has delayed planting of corn and soybeans in some regions. While some may feel that the rush to plant may be the most important issue of the day in these situations, neglecting weed control should not be an option.
Although the cool and wet weather may have delayed planting, weeds have continued to grow at the same time, albeit more slowly perhaps. Burndown herbicides and residual herbicides will more than pay for the time and effort spent applying them. Remember the common used refrain- "Start Clean!"
Weeds compete with newly seeded crops for space, light, moisture and nutrients. Weeds have the potential to reduce yields in all crops. Weeds have a head-start on crops if not controlled with a burndown. A classic case for soybeans is illustrated by research from Michigan State University that shows a 12% loss in yield if herbicides were applied at the 1st trifoliate stage of growth, rather than 7 days before planting.
Delays in burndown leads to a more aggressive approach towards weed control. Increasing rates of glyphosate can be helpful, along with using 2,4-D ester and/or dicamba where feasible. Even if this means waiting 7 days before planting some crops. Hard to control, and/or resistant weeds like marestail, may require applications of glyphosate, 2,4-D and metribuzin or saflufenacil. Including residual herbicides is also a good practice too.
Below are several good web sites that explain more fully the burndown options to use when planting is delayed.
Don't Skip Burndown Herbicides Applications this Spring
Adjusting No-till Burndown Programs for Later Planting