By Bob Hartzler, Department of Agronomy
Weeds present at planting time in no-till fields are commonly controlled by adding 2,4-D to glyphosate. Its use broadens the spectrum of weeds controlled, provides more consistent control during cool weather, and reduces selection pressure for glyphosate resistance compared to glyphosate only. The primary disadvantages of including 2,4-D are the added cost and the potential for crop injury.
Crop injury risk is minimized by following the planting delays stated on product labels. Ester formulations are recommended over amine formulations for pre-plant applications, due to a slightly shorter half-life and less mobility in the soil profile. Planting seed at the proper depth and ensuring closure of the seed furrow also is important in managing risks.
The restrictions regarding corn planting are based solely on injury risk and vary among manufacturers. For soybean, the restriction is based on both injury risk and residue tolerance, therefore they are uniform on all products.
Planting restrictions following pre-plant applications of 2,4-D. (Rates are based on products containing 4 lb a.i. per gallon. )
2,4-D ester — 7 days following 1 pt; 30 days following 1-2 pt
2,4-D amine — 15 days following 1pt; 30 days following 1-2 pt
2,4-D ester or amine: 7 days following 1 pt 4 lb/gal; 14
days following 1-2 pts
Bob Hartzler is a professor of weed science with extension, teaching and research responsibilities. He can be contacted by email at firstname.lastname@example.org or phone (515) 294-1164.