Illinois Field Crop Applicators Practice Test

What is indicated by the need for increased herbicide rates when conditions are dry?

1. Weeds are actively growing

2. Weeds are dying

3. Weeds are resistant

4. Herbicides are ineffective

The correct answer is: Weeds are actively growing

The need for increased herbicide rates under dry conditions is primarily linked to the fact that weeds are actively growing. During periods of drought or low moisture, weeds can exhibit stress, but many species can also adapt by allocating resources to their roots and making them more resilient. An active growth phase means that the weeds are photosynthesizing and taking up nutrients, which can enhance their uptake of herbicides. When weeds are actively growing, they are more likely to absorb the herbicide effectively, improving the potential for the chemical to work against them. However, dryness can also lead to reduced herbicide efficacy overall. Therefore, in certain situations, practitioners may consider increasing the dosage to ensure that the herbicides have the necessary potency to combat resilient, actively growing weeds despite non-ideal moisture levels. The other options suggest scenarios where the effectiveness of applying herbicides might be limited or altered, which doesn’t align with the reasoning for increasing rates in response to active growth in dry conditions.