Seed certification programs allow only a very small level of PLRV in certified seed. In Idaho, for instance, during the second field inspection the allowable amount of PLRV is only 0.05% for G4 seed, 0.01% for G3 and G2 and none at all allowed in nuclear and G1. Very small percentages of PLRV in seed potatoes do not normally pose any risk for the commercial producer. However, even very small percentages of virus can be a problem if green peach aphids appear very early and in abundance. In years that are very favorable for insects, like the 1996 season was, the aphid population can become so large that even a very low percentage of PLRV infected seed could result in sufficient spread to cause a problem, because as the aphid population increases, so does the probability that they will encounter an infected plant. Control of aphids with insecticide application is the only means of managing this problem in production years that are highly favorable for aphids.