Illinois Field Crop Applicators Practice Test

What condition indicates a need to apply a lower labeled rate of a soil applied herbicide?

1. High organic matter percentage

2. Herbicide applied alone

3. High soil texture in sand

4. High crop residue soil cover

The correct answer is: High soil texture in sand

Applying a lower labeled rate of a soil-applied herbicide is necessary when dealing with a sandy soil texture. Sandy soils have larger particles and greater drainage capabilities, which can impact herbicide efficacy. Because of their lower ability to retain moisture and nutrients, herbicides can break down or leach away more quickly in sandy soils. Therefore, utilizing a reduced rate can help mitigate the risks associated with rapid degradation and enhance the effectiveness of the herbicide by ensuring that the active ingredients are utilized over time without excessive application that could lead to runoff or environmental concerns. Other factors such as organic matter, herbicide interactions, and crop residue also play a role in application rates but do not specifically indicate a need for reduction in the same straightforward manner. High organic matter can improve herbicide binding and retention, meaning that a standard or higher rate might be more appropriate in such conditions. Similarly, applying herbicides alone rather than in a mixture could affect the overall efficiency but doesn’t necessitate a reduction in rate. High crop residue cover can sometimes enhance soil moisture retention but typically doesn’t require a reduction in dosage either.