When it comes to effective weed control, timing is always critical. But it is particularly important when you are using a total post program since dead weeds with late spraying can still trim your yields.

In fact, you may be losing as much as 0.7 bushels per acre for every inch of additional weed growth due to late spraying, indicate Southern Illinois University weed scientists. This represents a potential profit loss of as much as $5 per acre for every inch of weed growth.

Post-emergence programs make the timing of herbicide applications more important than ever, says Mike Johnson, technical brand manager for corn herbicides with Syngenta Crop Protection. When deciding when to apply herbicides in a post-emergence program, he says, you need to look at the specific weed problems, population density, nutrient deficiencies and moisture stress.

Timely Application.

Johnson says Corn Belt growers can expect to have some years when they have only one day (or even less) to make an in-time application of glyphosate in herbicide-resistant corn for maximum effect. “Missing this window can be extremely costly, ” he says. “A 1-week delay can result in a yield loss of 5 percent, while a 2-week delay can cost you 10 percent of your yield.

“If you are relying strictly on glyphosate, there may be a need to make at least two precisely timed applications to minimize your yield loss. These two applications are even more unlikely to occur on time. In a corn and soybean rotation, the ability…