Illinois Field Crop Applicators Practice Test

When should a higher rate of herbicides be applied for postemergence?

1. Weed size is small

2. Weed density is low

3. Adjuvants are used

4. Conditions are dry

The correct answer is: Adjuvants are used

Applying a higher rate of herbicides for postemergence is often recommended when adjuvants are used. Adjuvants enhance the efficacy of the herbicide, improving its ability to penetrate plant surfaces and increasing its uptake by the target weeds. When herbicides are applied with adjuvants, they can work more effectively, which may warrant a higher concentration of the active ingredient to ensure maximum coverage and weed control. In contrast, applying herbicides when weeds are small or when weed density is low typically allows for effective control at lower rates, as young, smaller weeds are generally more susceptible to herbicides. Similarly, in dry conditions, the effectiveness of herbicides can be reduced since moisture is often required for the herbicide to work correctly, and higher rates may not be necessary or even beneficial in such situations.