When are insecticide sprays most effective against leaf-feeding insects?

Insecticide sprays are most effective against leaf-feeding insects when the leaf feeders are still small. At this early stage, the larvae are typically more susceptible to the effects of pesticides because their bodies are smaller and they have not yet developed strong feeding habits or resistance. Young larvae consume plant material more eagerly, which means they are likely to come into contact with the insecticide as they feed on treated foliage.

Applying insecticides when the insects are in their smaller, early instars also minimizes the overall damage to the plants, as there is less time for the insects to strip leaves or cause significant harm to the host plant. In contrast, larger larvae are often more resistant to insecticides and can cause more extensive damage before control measures take effect. Similarly, applications when host leaves are browned typically indicate stressed plants that may not effectively absorb the pesticide, and treating after several days of feeding allows the pest to establish a stronger presence, making control much harder.