Once we reach mid to late June, alfalfa growers should be scouting their fields regularly for potato leaf hoppers (PLH).  The PLH does not overwinter in Ohio.  It arrives each year when it is carried northward from the Gulf Coast region on storm fronts.  After they arrive, PLH will reproduce and approximately three weeks are required to go from egg to adult.  We can see high numbers of PLH as we get into July and symptoms of damage from this sucking insect include yellowing of leaf tips.  By the time symptoms are seen there will already be yield and quality loss associated with stunted plants.  PLH feeding can also cause slower regrowth and stunting of subsequent cuttings, so yield losses are compounded.  

Growers should be scouting fields before any visible sign of damage is presented.  Scouting involves the use of a sweep net.  Fields should be sampled at 3 to 5 random locations.  A single sample is composed of 10 pendulum sweeps of the net.  After each 10-sweep sample stop and count both the number of PLH nymphs (wingless development stages of the adult) and adults.  Get an average height measurement of the alfalfa.  If the number of PLH nymphs and adults are greater than the average height of the alfalfa, then either an early harvest or a rescue insecticide treatment should be considered.  The exception to this threshold treatment number is if the field is planted to a glandular hair PLH resistant alfalfa variety.  The presence of hairs on the alfalfa plant interferes with normal PLH feeding and slows nymph development.  The threshold treatment level for these varieties of alfalfa is 3 times higher compared to non PLH resistant varieties.

Early harvest of alfalfa that is above the treatment threshold can temporarily eliminate nymphs by removing their food source and it will cause the adult PLH to disperse and look for another food source.  This is a good option if the harvest date is close and/or the pre-harvest interval of an insecticide rescue treatment would interfere with a planned harvest.  However, growers must be aware that regrowth 1 to 2 weeks following harvest will be attractive to PLH adults and so scouting of that next harvest regrowth must begin early on.

For more information about scouting for PLH and/or insecticide options for a rescue treatment, contact the Wayne County Extension office at 330-264-8722.