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THE EPIDEMIOLOGY OF PLUM POX VIRUS IN MOLDAVIA.*
In spring and in early summer they migrate from stone-fruits onto grass plants where they feed and replicate during summer, and in autumn return onto fruit trees.
Under conditions of Moldavia this period coincides with the end of September and the whole of October.
In spring after moulting of aphids on winged individuals they lose the virus and do not make any attempt to feed on plum trees.
Therefore nonviruliferous aphids migrate.
Plum pox virus has not been found on grass plants and in autumn nonviruliferous aphids remigrate onto fruit trees.
Thus, during summer plum pox virus does not spread and in autumn trees are infected through the remigration of aphids onto fruit crops and their movement from infected onto healthy trees.
Except of fruit trees the source of the virus is Prunus spinosa.
This circulation scheme of plum pox virus conforms to the rate of its natural distribution : from 0.9% to 3% a year in gardens where some trees have been already infected.