By Darren Hefty

Controlling grassy weeds in a grass crop like corn is critical in your effort to raise top yields.  Corn determines its yield early in the season.  Taking care of weeds before they emerge eliminates weed competition for nutrients, water, and sunlight.

GRASS CONTROL

When it comes to grass control, especially with foxtails, there are a number of good herbicides.  The performance of Harness, Surpass, Dual II Magnum, and Outlook is excellent provided you get some rain to get them in the soil solution and ultimately into the weeds.  If you’re in dry country or in no-till, apply your pre-emerge herbicides early enough to give yourself time to catch a rain or two and make the herbicides work to their potential.  If you’re doing conventional tillage, we prefer to see the herbicide applied before or during tillage, as long as that tillage is kept shallow.

If you apply your pre-emerge grass control herbicide after you plant, don’t wait too long.  I understand if you’re moving a lot of soil with your planter that you may see some streaks in the row if you put your herbicide on before planting.  The caution is if you wait too long after planting, some weeds could already have germinated or, worse yet, emerged and have begun competing with your crop.  Also, if you wait until after planting to apply your pre-emerge herbicide, there’s no good way to incorporate it if you don’t get timely rainfall or irrigation.

For problem grasses like field sandbur, Italian ryegrass, johnsongrass and the like, none of the pre-emerge herbicides I’ve mentioned so far are great.  However, these pre’s can take out the foxtails and many of the small-seeded broadleaf weeds in your fields, greatly reducing the weed competition.  This should preserve your yield potential and afford you a better chance to get good coverage on the tough weeds with your post-emerge application.  Alternatively, you may consider using Eradicane for help on sandbur and johnsongrass in a conventional tillage program.

BROADLEAF CONTROL

Good grass control is not enough anymore.  You want broadleaf control from your pre, too.  For that reason, the chemical manufacturers are premixing the aforementioned grass control herbicides with various broadleaf compounds.  I like this idea, but there are certainly some things to watch out for.  Here’s my list.

  1. Wrong ratios of product – We’ve seen it for years with the atrazine premixes like Bicep and Harness Xtra, where the manufacturer puts so much atrazine in the mix that you have to cut the rate to avoid potential groundwater contamination or carryover to next year’s crop.  Now, you have to watch products like Corvus, SureStart, TripleFlex, and Verdict to make sure the ratio fits for your soil characteristics and crop rotation plans.
  2. Mixing Problems – This is another issue we’ve seen, especially with the atrazine products.  Will they mix with your liquid fertilizer or with other products you may want to apply?
  3. Premixes could settle out – Any time you have two or more products premixed together in a jug or tank, you have the potential to see them settle out when stored for any amount of time.  Be careful to follow the manufacturer’s recommendations to keep your premix in solution so when you’re applying it you get the correct ratio of the products.  Think of the disaster if you had a low use-rate product like Callisto or Laudis in the premix and sucked that out of the bottom of the tank so you had 3 or 4 times as much of it as you intended per acre.
  4. Negative interaction with other crop protection products – This one is huge, so please read this again before applying anything on your cornfields.  Organophosphate insecticides like Lorsban, Counter, Fortress, Aztec, SmartChoice and others can lead to a very bad reaction within your corn plants if you apply an ALS or HPPD herbicide.  Here’s one example: TripleFlex and SureStart are premixes that contain Python, an ALS herbicide.  If you applied some Counter for rootworm control and used TripleFlex for your herbicide, you may take 50 bushels off your yield from the negative interaction in the corn plants.  The more systemic the products are, the worse the issue can become.  This isn’t always a big deal, but why take a chance?  Pick a different herbicide or a different insecticide.
  5. Unrealistic expectations/Over-marketing – Everyone wants the one-pass solution to weed control.  Guess what?  It doesn’t exist.  I support your decision to consider a premix for improved pre-emerge weed control.  Just don’t expect it will kill every weed season-long.