A pre-emergence herbicide application will help keep late-emerging weeds small and uniform enough in height to boost odds for success when following up with a post-emergence treatment. Using a pre-emergence herbicide buys you more time to apply your post-emergence herbicide for optimal weed control,” he says.
In addition, a pre-emergence herbicide can be an especially good investment with irrigation, which ensures moisture is available at the right time to activate the chemistry. When dealing with dry land cornfields using a residual pre-emergence program will still be beneficial in reducing potential problems with glyphosate-resistant weeds, even if a lack of rainfall delays activation past the ideal time for starting corn out in clean fields.
Timing is everything.
The main management focus should be on controlling those early weeds. Research conducted in Minnesota, and Wisconsin, shows that at about the V3-V4 stage, if weeds aren’t removed, fields will suffer an average 3 bu./acre/day yield loss up until the end of June. In fact, farmers should plan to have all their weed control completed by the Fourth of July.
Timing is important for both post- and pre-emergent applications. For pre-emergent herbicide applications, try to time them closer to when you plant, especially if you have a weed spectrum in the field that can emerge later in the season, such as waterhemp.
Weeds that re-infest after an initial herbicide application can also be very competitive. The SDSU recommends being vigilant to control these later weed flushes, if necessary, while they are also still small.
Avoid reduced rates.
Many farmers run reduced herbicide rates of soil-residual herbicides to save costs. However, with reduced rates, you may be setting the product up to fail earlier, depending on weather conditions and weed pressure. Using a full, or a nearly full rate based on soil type often provides an extended period of weed control that you don’t always have with reduced rates.
Especially in the post-emergence arena, good early season weed control has a lot to do with proper timing and not skimping on rates. Also, when you do post-emergence weed control, make sure you don’t go too fast and check to make sure you’re getting good spray coverage on weeds.”
Scout and reassess.
After each weed-control practice, producers need to scout fields and evaluate how well their treatment worked and whether or not a remedial treatment might be needed.
Source: SDSU iGrow