Maturity resistance
Potatoes are most susceptible to viruses when they are young. Resistance to viruses increases when they plants grow older.
The causes of maturity resistance are a slower multiplication of the virus in the plant and a slower transport of the virus from the green plant parts to the tubers.
Cultural practices should be such that maturity resistance is reached when the vector (i.e. aphid) population reaches a dangerous level.
Methods
Possible methods for achieving early maturity are:
- pre-sprouting of seed
- early planting
- take measures to promote a quick emergence
- moderate nitrogen application
Secondary growth and re-growth
A crop that has reached maturity resistance will become susceptible again when secondary growth occurs and when after haulm destruction re-growth of the haulm starts. Many cases are known of seed crops becoming heavily infested with viruses after re-growth.