SPREAD OF APPLE PROLIFERATION IN A NEWLY ESTABLISHED APPLES PLANTATION
The first trees infected naturally were noticed in 1972. While their number remained rather low for some time, it rose considerably in 1975 and 1976. The disease spread in the plots planted with virus-tested trees as well as in those with non-tested ones. The local position of the newly affected trees did not show any connection with the position of the trees infected experimentally. But in one plot that had been treated with insecticides only once or twice during springtime, diseased trees were much more frequent than in those plots in which a normal insecticide application had been carried through in spring and summer. In other apple tree orchards, too, where only few sprayings had taken place, attacks by proliferation were often very strong in 1975. The spreading of the disease seems to be furhered when applications of insecticides are reduced considerably.