It is apparent in a number of corn fields that the Pre applied herbicide has given out.  In fields where the weed control is relying completely on a Pre applied herbicide, weeds, particularly Palmer amaranth, are emerging. The picture at left shows emerged Palmer amaranth which came up in the last 10 days after, in this case, Lexar applied in early April had played out. Contrast this to the picture where Halex GT was applied on V2 corn which even now (V6) is still clean.  I have seen similar good results with Capreno, Bicep or even Lexar applied early Post in corn. This really illustrates how early Post herbicide applications will often provide more consistent weed control than herbicides applied Pre in corn. Corn that is weed free by V5 to V6 is well on the way to shading the soil enough to discourage late emerging weeds. The point is that Palmer emerging around V4 to V5 when Pre applied herbicides often play out will typically not be very competitive to corn.  However, Palmer amaranth, and other weeds, which become established around V4 to V5 corn will often produce a large seed bank that will be a problem in next year’s soybean or cotton crop.