Why shouldn't insecticides be allowed to stand in the spray tank?

The correct rationale for why insecticides should not be allowed to stand in the spray tank over time is that diluted insecticides may lose their effectiveness or potency if they sit too long. When insecticides are mixed with water or other carriers, chemical reactions can occur that may reduce their efficacy in controlling pests. Factors such as light exposure, temperature, and pH can contribute to their degradation. Additionally, some formulations might separate or settle, which can affect the uniformity of the application. Therefore, it's essential to prepare only the amount needed for the application and to avoid leaving any diluted insecticides in the tank for extended periods.

Other options, while they may present potential concerns, do not directly relate to the main reason insecticides should not remain stagnant in the tank as significantly as the loss of strength due to chemical changes.