Whether you’re feeding foliar nutrition or managing pest pressures, effective spray applications are key to maximizing yields and your operation’s return on investment.
While planning for and executing a spray application requires numerous decisions — application timing, rate calculations, branded chem vs. generic choices, tank mix or premix selection, adjuvant usage, and more — there are really three main considerations to prioritize as you plan.
The type and size of weed growing in your fields will guide your herbicide and mode of action selections, but it will also determine the type of spray nozzle you’ll want to use. While many broadleaf weeds with larger, more horizontal surfaces are well suited for larger, coarser sprays, grasses and young broadleaf weeds need finer sprays for effective control.
Staying on top of weed pressure in your fields early can pay dividends later in the season as it’s easier to control smaller weeds than larger ones.
Remember, the optimum temperature for photosynthesis in waterhemp ranges from 68-104°F, meaning these naturally drought tolerant weeds can emerge, grow, and thrive even in hot temperatures.
(Always read and follow label directions to ensure you’re making the right decisions for your selected herbicide.)
How to Choose the Right Spray Nozzle
Temperature also plays a significant role in spray efficacy. Hot, dry weather can cause weeds to close their stomata and slow down their processes, reducing herbicide impact.
To ensure your chem applications are still effective in the summer heat, keep the following tips in mind:
The best temperature to spray Roundup® is between 45-90°F. Applying translocated herbicides, including Roundup® brand herbicides or comparable generic herbicides like AgSaver™ Glyphosate 53.8% or Willowood Glypho 6, in hot, dry conditions can result in delayed or reduced weed control. Plants conserve water by thickening their leaf cuticles and reducing translocation and metabolism in dry, high temperatures, thus causing problems with herbicide absorption. Consider using higher labeled rates to help offset these thicker cuticles and lower translocation rates.
Including the full rate of ammonium sulfate (AMS) at 17 lbs per 100 gallons of spray solution can help maximize glyphosate uptake by target weeds, especially if hard water is a concern.
Consider using a surfactant, such as methylated seed oil (MSO) and/or crop oil concentrate (COC), to improve the efficacy of herbicides in warm weather, especially in weeds with thick cuticles like lambsquarters.
Be advised that tank mixes containing COC can lead to enhanced crop injury when applied under hotter conditions; if a non-ionic surfactant (NIS) is an option, consider using that instead.
What’s the Difference Between Crop Oil Concentrate and Methylated Seed Oil?
Finally, crop development stage also impacts herbicide, insecticide, and fungicide application timing. In corn and soybeans, this timing can be based on:
Growth stage
Crop height
Harvest interval required
Be sure you know these specifications for any and all chemicals you’re planning to use on your crops and conduct field scouting to determine the optimal spray timing.