Along with the risk index you need to take into account the following
factors when considering the risk of virus spread.
- Mature plant resistance. Crops are generally at their most vulnerable within the
first four weeks from emergence. After this time 'Mature Plant Resistance' builds up which makes it more
difficult to transmit virus within the crop.
- Cultivar resistance. Different varieties of seed will have different inherent
natural resistance to PVY. Using a more resistant cultivar will reduce the risk of virus transmission.
- Volunteers and seed quality. In most situations it is unlikely that aphids will
bring PVY into your crop (see next note). The greatest risk is from aphids spreading what little
virus may already be present. This can come from two possible sources. Volunteers from previous potato
crops and low levels of virus in the seed planted.
- Surrounding crops. The risk of aphids spreading PVY to your crop from elsewhere
is increased when ware crops are grown close to your seed. This is because there will be greater
numbers of aphids and ware crops generally have a higher incidence of virus present.