Jordan question:

Getting some questions on threshold for yield loss from leafhopper?

Brandenburg:

There is not a good one. Work was conducted 40 years ago and the studies were not very robust.  They are a problem because you really can't do the work in a greenhouse, you cannot simulate damage that involves a toxin, populations often crash on their own, and the distribution in the field is rarely uniform.  We stick with 25% of the leaflets with damage AND the presence of leafhoppers. While the data supporting that number are not great, it beats just simply guessing.