The potato leafhopper continues to be the most serious insect affecting alfalfa production in Ohio. We conducted a special study with established alfalfa at The University of Findlay Equestrian & Pre-Vet Center to emphasize the importance of the economic threshold of the potato leafhopper and determine the amount of reduced alfalfa yield and quality that actually happens as a result of the crop damage. We designed a 4x replicated research plot which involved collecting quality and yield data for each hay cutting. Potato leafhopper insecticide treatments was varied in the following ways:

* No spraying
* Spraying every two weeks
* Spraying at established economic threshold
* Spraying 1 1/2 times over established economic threshold.

Potato leafhopper scouting was completed on a weekly basis, along with 15 one acre adjoining alfalfa variety plots. Potato leaf hopper populations seemed to get a very early start and continued very intensely throughout the 1995 growing season. Table 1 shows data recorded for potato leafhopper populations starting on June 22, 1995 (one week after lst cutting). At this early point, PLH populations were already over threshold and spray treatments were applied on plots to be sprayed every two weeks, at threshold and at 1 1/2 times over threshold. Because of the high intensity of PLH populations the plots to be sprayed at and over threshold were being sprayed the same time as those being sprayed every two weeks. This occurrence happened three out of the four spray treatments which is unusual for normal PLH infestations.

On the fifth week into the second cutting growth, the plots not sprayed were 5.5 inches shorter than those sprayed. There was also a very great visual difference comparing the sprayed plots (very green) with the non sprayed (very yellow). The PLH populations also had a tendency to still remain higher than normal after the second cutting was removed as high nymph populations were noted.

Yield results are indicated in Table 2. As expected before PLH arrived the first cutting yields show no significant difference with p=.98. The second cutting yields are approaching more difference but still not significant with p=.58. The third cutting yields did show significant difference with p=.10.

Forage Quality comparisons are recorded in Table 3. Very little difference in quality was noted throughout the project except for protein data from the second cutting. The plots not sprayed had significantly lower protein with p=.05 but this did not follow through in the third cutting.

Conclusions:

2. In years of high PLH intensity, a minimum of scouting every two weeks is needed to keep up with the growing population.

3. Cutting the alfalfa can reduce PLH populations but PLH thresholds can be reached in ten days or less.

4. PLH nymphs can be very significant since they cannot travel making high PLH populations in stubble during the first week after a cutting.

5. This research needs to be continued in 1996 using the same plots with the same treatments. It is highly probable that due to stress, the plots not sprayed could have a thinner stand.

Extension Program Implementation:

Return to Ohio IPM Home Page.