This Spring has presented plenty of challenges, and another is coming in from the south. Potato leafhoppers (PLH) are being carried into Ohio fields on southern winds and can quickly become a concern. PLH arrives around the time of first cutting and can be a pest of alfalfa into September. PLH can reach maturity in three weeks, and multiple generations can be present at the same time, being very damaging.
PLH is relatively easy to identify; the adults are lime green, wedge-shaped, and are roughly 1/8 of an inch in length. The immature nymph stages look similar but are smaller and lack wings. PLH feeding damage, commonly called hopper burn, is seen as the yellowing of alfalfa leaf tips in a V-shaped orientation.
For a video on identifying PLH, follow this link: PLH Identification and Damage in Alfalfa 
Just like every pest, scouting is critical to know when spraying is an economically sound decision. To scout PLH, a 16-inch diameter sweep net, and a yardstick are needed. Be sure that the sweep net is 16 inches in diameter; if not, the control thresholds will not be accurate. With the sweep net, take 10 pendulum swings, making solid contact with the field canopy. After 10 swings, count the adults and nymphs collected, and be sure to check the seams around the rim for PLH nymphs. Take multiple samples from around the field for more accurate estimates. It is best to sample in dry and calm conditions.
For a video demonstration of PLH scouting, follow this link: Scouting for PLH in Alfalfa
The threshold for when control should be considered is 1 PLH for 1 inch of stand height. For example, if the alfalfa is 16 inches in height, the threshold for control would be 16 PLH adults and nymphs per 10 swings.
If a field has reached the threshold where action is needed, there are some extra considerations to give thought to. If the alfalfa is close to harvest, be sure to account for the preharvest interval restrictions for insecticides; there may be instances where an early or timely harvest is the better choice. Be sure to monitor the following cuttings for continued PLH pressure. PLH is most damaging to young stands, fresh regrowth, and stressed stands, since feeding can remove a great percentage of leaf area compared to a healthy mature stand.
For more information on potato leafhopper, see this factsheet: Potato Leafhopper on Alfalfa