How long is pyrethrum spray effective?

Pyrethrum spray typically remains effective for about 1 to 3 days after application, depending on environmental conditions such as sunlight, rain, and temperature. Its residual potency can vary based on the surface it is applied to and the presence of other factors like humidity. For optimal results, it’s often recommended to reapply the spray after heavy rain or if it appears to have diminished in effectiveness. Always check the product label for specific guidance on duration and reapplication.