Adult potato leafhoppers are very abundant at present in potato fields throughout the region.  Nymphs are now beginning to appear.  Adult leafhoppers insert their eggs in leaf veins and petioles.  The eggs take about 10 days to hatch.  Potato leafhopper nymphs are found almost exclusively on the underside of the leaves and will be most abundant mid-plant.  The first instar nymphs are very small, narrow and almost translucent. Older nymphs are a vivid lime green.  Wing pads can be easily discerned by third instar.  The insect has five nymphal instars.  The economic threshold is very low, in the range of 10-15 leafhopper nymphs per 10 leaves (true leaves not leaflets).  It is important to apply insecticidal controls before late instar nymphs are present.  Plant damage occurs before the classic symptoms of "hopperburn" become evident.   There is controversy about how damaging adult leafhoppers are.  It is not common in Minnesota for potato leafhopper injury to occur before nymphs are present.  In some cultivars insecticidal treatment may be justified if adult leafhoppers exceed 1 per sweep.  Nymphs should be sampled by plucking  leaves.  Sweep nets do not work well for sampling nymphs because the insects are small, soft-bodied, and easily crushed.  Many seed growers and  some commercial growers use nicotinyl insecticides (Platinum or Admire) at planting.  These treatments provide reasonably good early season potato leafhopper control.  If potato leafhoppers require subsequent treatment in nicotinyl-treated potatoes a foliar spray of a different insecticidal class should be used. This is important because a second application of a nicotinyl insecticide could hasten development of insecticide resistance in Colorado potato beetle.