Low aphid population periods
Aphids are the main vectors of viruses. Where possible seed potatoes are grown in the periods of the year and/or areas when the aphid population is low.
Netherlands
In the Netherlands the population of Myzus persicae often stays low until the middle of July. Then the population builds up.
Aphid population Netherlands
When the aphid population has grown too big and the aphids start to migrate (winged aphids) the haulm of the seed potato crop are destroyed to restrict infection and prevent the transport of any virus to the tuber. It is generally assumed that critical levels of aphids are reached when more than 5 winged aphids (Myzus persicae) are caught per trap within a week (or 2 aphids per day on two successive days) or when more than 20 aphids are counted per 100 leaves.
Highlands
Highlands are known as areas with low aphid populations and viruses are no real constraint in seed production. The degeneration is low and temperatures are moderate. These moderate temperatures allow storage of seed in natural ventilated stores.
Lowlands
At low altitude, where potatoes are grown following a hot summer, during autumn and winter, it is possible to escape virus infection. At first the aphid population is relatively small and the risk of spreading viruses is less than when the potatoes are grown later during the winter season. To avoid virus problems here seed is produced in the early autumn crop. As an example the solution of India (Puskharnath) where by shifting the season towards the early autumn season it became possible to produce seed at low altitudes.
Aphid population Punjab