This is an image of burn from potato leaf hopper feeding. The insect vectors a toxin that causes damage to the leaf. Several insecticides can control this insect pest, including pyrethroids. The threshold is around 25% of leaves with burn. Make sure leaf hoppers are active and that you are treating the insects and not the damage from the insects (populations can crash quickly.) Use caution when applying insecticides, especially pyrethroids, under hot and dry conditions. We need to avoid flaring spider mites.