Posted 21 August 2010. PMN Crop News.
Check for Alfalfa Leaf Hoppers
Source: University of Illinois Press Release. aces.illinois.edu
Urbana-Champaign, Illinois (July 26, 2010)--Potato leafhoppers are making their presence known in some northern Illinois alfalfa fields. These small, pale-green, wedge-shaped insects represent a potential economic threat to alfalfa every year. Since their population varies from year to year and field to field, monitoring a field using a 15-inch diameter sweep net is the only way to accurately determine leafhopper densities.
Potato leafhoppers "arrive" in Illinois each spring from southern states on wind currents. Depending upon temperatures during the summer, three to four generations occur each year. Thus, fields should be checked through August. Typically, regrowth from cutting is most at risk for damage from leafhoppers.
The insect has piercing and sucking mouthparts and hence remove fluids while injecting toxins into the alfalfa's vascular system. Plants that have been fed upon display the characteristic "hopper burn", a v-shaped yellowing at leaf tips. Once this symptom is seen, the damage has already been done and cannot be corrected.
New alfalfa seedings typically are most susceptible to damage including stands growing under a cover crop. Taller alfalfa plants are able to tolerate more leafhoppers.
Insecticide application to conventional alfalfa (as compared to leafhopper resistant alfalfa) is justified at these combinations of alfalfa height and potato leafhoppers per one sweep: under 3 inches, 0.2 leafhopper; 3 to 6 inches, 0.5 leafhopper; 6 to 12 inches, 1 leafhopper; and 12 inches or taller, 2 leafhoppers.
Leafhopper population is inhibited in highly resistant varieties once the stand has become established. The treatment threshold for leafhopper resistant alfalfa may be 10 times greater than conventional alfalfa (see above paragraph).
Be sure to read and follow label directions when using any pesticide.
For further information and details on the life cycle and management of potato leafhoppers, see a University of Illinois fact sheet available at ipm.illinois.edu/fieldcrops/insects/potato_leafhopper/index.html or from local Extension offices.