Field corn in a rotation is an outstanding way to combat herbicide resistance. However, it is very important for growers to implement some type of post-harvest strategy to prevent weed seed rain, or deposits to the seedbank, from occurring in fallow fields, or risk wasting many years of hard work.

Before implementing any post-harvest strategy, a three questions need to be considered:

If the weeds are taller than 6 to 8 inches, you really have no choice but to mow and/or disk.  A giant pigweed plant in any row crop cannot be consistently controlled, so there should be no reason to expect something different in a fallow field.

Personally, I am a big fan of tillage as a post-harvest strategy.  I prefer the smell of freshly tilled ground and the silence of dead weeds! Good news is diesel prices are down compared to this same time last year (approximately -7.5 percent).  This should make the mow/till pill slightly easier to swallow.  Both Palmer amaranth and Benghal dayflower/tropical spiderwort plants can easily produce another crop of seed from September to November, thus tillage will need to be conducted on a monthly basis until first frost or shortly before.

If herbicides are preferred, I would suggest a tank-mixture of Gramoxone + Dual Magnum in most situations.  2,4-D or dicamba could also be included in this mixture if plant size is questionable.  Feel free to substitute your favorite generic formulations of these herbicides.  There are too many of these to specifically mention. 

Post-harvest applications of Dual Magnum should be avoided if a small grain will be planted this fall.  Dual Magnum has a 4.5 month rotation restriction for barley, oats, rye or wheat.  Small grain planting should be delayed by at least 10 days for each 16 oz/A of 2,4-D applied or 15 days for each 8 oz/A of dicamba.  If cotton, peanuts or soybeans are nearby, remember cotton is generally more sensitive to 2,4-D drift while peanuts and soybeans would be more sensitive to dicamba drift. 

Growers in Georgia have made tremendous strides in their battle against herbicide-resistant Palmer amaranth and other weeds over the last 12 years.  It has been a tough fight.  Unfortunately, the fight is not over after field corn is harvested.  Weed seed rain must be prevented in fallow fields.  As always, good weed hunting!