Illinois Field Crop Applicators Practice Test

What condition suggests using a lower rate of herbicides for postemergence application?

1. Weed size is large

2. Weed density is high

3. Adjuvants are not used

4. Conditions are dry

The correct answer is: Conditions are dry

Using a lower rate of herbicides for postemergence application is often suggested under dry conditions. When conditions are dry, the efficacy of many herbicides can be diminished. This reduced effectiveness may be due to the lack of moisture needed for the herbicide to activate and move within the plant. In these situations, using a lower rate can mitigate potential crop injury while still providing some level of weed control, as higher rates may not be fully effective without sufficient moisture. The other factors, such as large weed size and high weed density, typically necessitate higher herbicide rates to ensure control. Additionally, the inclusion of adjuvants often enhances herbicide performance; therefore, their absence would not suggest a lower rate but rather reinforce the need for adequate herbicide application rates to achieve effective control in adverse conditions.