Scouting alfalfa fields is the key to early detection of potato leafhopper infestations. Use a 15-inch diameter sweep net to determine the potential risk a potato leafhopper infestation may pose to your alfalfa.
Scouting for potato leafhopper starts after the first cutting of alfalfa (about the first part of June) till the first fall frost. You will want to use a potato leafhopper sequential sampling plan to determine if an infestation requires management or not. The first thing to do is determine the height of your alfalfa. Smaller plants are more vulnerable to potato leafhopper; thus there are different action thresholds for different heights of alfalfa. The second thing you will need to know is how to sample for potato leafhopper. A sample consists of a set of 10 sweeps of the net. A sweep is one pass in front of you as you walk through the alfalfa. The return swing is counted as another sweep. Sequential sampling reduces the time spent in each field and tells you whether to treat (management action) or not treat (no management action). Sequential sampling is particularly helpful in minimizing time required to make a management decision in situations where PLH populations are very high or very low. Use the following chart to determine potato leafhopper infestation levels.
Write down the number of potato leafhoppers for each sample taken on the card. Add each sample to the next, keeping a running total of potato leafhoppers. You will need to take at least 3 samples using the sequential sampling method. On the sequential sampling card “N” is defined as no treatment (no management) needed at this time and “T” is defined as treatment (management) needed within in a week. If the sample is smaller than the “N” number stop and scout 7 days later. If the number of leafhoppers is larger than the “T” number then management action needs to be taken within a week. If the number of potato leafhoppers fall between “N” and “T” then continue and take the next sample till a decision can be determined. A guide with a printable version of the sequential sampling chart can be found at: http://www.nysipm.cornell.edu/publications/plh.pdf
Source: Growing Alfalfa the IPM Way