It is amazing how much effort folks put into having a successful bird shoot come dove season in Georgia. The following recommendations are the best we can do for keeping Palmer amaranth (pigweed) from ruining the view.
Row crop farmers have known for a while what it is like to battle resistant weeds. Now the battle is moving into the bird fields. Resistance to glyphosate has been documented since 2005 in our area. more recently we have discovered pigweed that has resistance to atrazine and to ALS inhibiting herbicides like Beyond or imazamox.
So how do we control pigweed in a sunflower field if there is resistance to so many herbicides? We have to keep it from ever getting out of the ground by using residual herbicides. Even then we have to realize that residual herbicides are not going to last the entire season. If you want a completely weed free field you will have to rely on herbicides, plus cultivation, hand weeding and/or hooded sprayer applications.
So what is the best system? begin by applying a yellow herbicide like Prowl or Treflan and incorporating it 2-3″ prior to planting. After planting it is probably best to apply Spartan Elite or BroadAxe due to mixed modes of action. Other options are to apply Spartan Charge (4 oz/A) after planting or Zidua SC (2.5 oz/A) which can go on after planting or postemerge from V1 to V8. It is important to realize that all of the preemerge options contain PPO inhibitors so we should not spray more than one per season.
After emergence you can use Beyond to control any susceptible escaped weeds, or a hooded application of a Aim which is yet another PPO inhibitor.
I tell you all this for a couple of reasons. We only have 5 different modes of action for controlling pigweed in sunflowers. Of those 5 all but one are only effective if put out prior to weed emergence. The one postemerge herbicide labeled for broadleaf weed control is Beyond and we are positive that we have resistance to this mode of action in our area.
If we spray sunflowers multiple times with limited MOA’s we run the risk of creating resistance to another class of herbicide. If we do that it will be extremely difficult to do anything with pigweed. So any pigweed that escapes your sunflower weed control program needs to be plowed, hoed or pulled. Allowing escaped weeds to go to seed is a great way to create resistance.
The only good news is that if we get resistance to all of the herbicides we can save money because we won’t have to purchase Clearfield sunflowers. Sharpen the hoes and keep resistance out of our area.