Why control weeds early?
• Early control helps protect yield potential of the crop.
• Small weeds are easier to control.
• Young weeds absorb and translocate herbicides better.
• Herbicides can be less effective during times of heat and drought stress, which often occur at later application times.
Sequential weed control programs, including preplant / preemergence (PRE) followed by postemergence herbicides, have consistently provided the best weed control and greatest net returns.
Critical period of weed control
• Defined as the growth stages or time during which weeds must be controlled to maintain maximum yield potential. Assumes the field is clean at planting time.
• Corn: weeds can reduce yield as soon as the V2 stage. Control weeds earlier than this and maintain control through at least V14 to help ensure maximum yield potential.
• Soybean: control weeds within the first four weeks. Maintain control through canopy closure. Preventing weed seed production: Control weeds to minimize competitive effects but also to prevent seed production, especially for glyphosate-resistant weeds like waterhemp, Palmer amaranth, and ragweeds.
Take the time to apply preplant / PRE herbicides
• Weeds that germinate, emerge, and grow with the crop cause the most yield loss.
• Preplant/PRE herbicides provide critical early-season weed control when crops are most sensitive to competition.
• Preplant/PRE herbicides can widen the window of application for postemergence herbicide sprays.
• Total post programs are more risky because weather conditions may prevent timely application.
• Control weeds BEFORE they start to compete.
If preplant / PRE herbicides were not applied:
• Apply postemergence herbicides as soon as possible.
• Include residual herbicides to extend control of weeds that are still germinating.
• Do not cut the use rate. Use the recommended rate for the weed size.
• Use high-quality adjuvants as directed on the product labels.
• Be prepared to apply follow-up treatments to control escapes and late-germinating weeds.