Potato leafhopper on raspberry
Even though a high proportion of the leaves might be affected, it is often surprisingly difficult to find the leafhoppers themselves, which are tiny light green or yellowish-green wedge-shaped insects. The adults fly quickly when disturbed, so sometimes you can brush the foliage to see whether small light-green insects fly out that you can then try to track and identify. The nymphs however, cannot fly, and so are often more easily found. Adults or nymphs are found on the leaf undersides rather than the top, and will usually move sideways when disturbed.
Potato leafhopper early-instar nymph.
Damage is often most serious in new strawberry plantings, where the plants have few leaves yet and are dependent on a small amount of foliage. If the plantings are drought-stressed, growth slows even more. Damage then accrues on leaves which become marginally able to translocate needed photosynthates. This is just one reason why it is important to make sure that sufficient water and nutrients are available to the plants, and that leafhoppers are controlled with an insecticide if necessary.
Be sure to minimize toxicity to beneficials by choosing safer materials and apply them at times when bee exposure will be minimized. A number of insecticides are available that are effective.