Roguing
By roguing diseased or off-type plants are removed from a seed crop. This to avoid that the tubers which grow on the off-type plants or the diseased plants enter the seed lot and to avoid that other healthy plants become infected with the diseases present.
Roguing a------Roguing b
Virus diseases
The most common purpose of roguing is to remove virus diseased plants. Green plant parts and tubers are removed from the field. The roguing starts as soon as the first virus symptoms of diseased plants are visible.
The reasons for this are:
- to remove the infection sources before other plants become infected
- that it is easier to remove young small plants, than full grown plants
If present, it is recommended to kill the aphids before roguing ( the aphids on virus infected plants in many cases carry viruses and by roguing the virus infected aphids fall on healthy plants, which then become infected).
For practical reasons it is often recommended not to apply roguing in crops when the percentage of virus infected plants exceeds 2%.
Late blight
In case there are in a field in some places a few plants infected with Late blight it is useful to remove these infection sources. For practical reasons this measure often only applies for smaller sized farms and when the infection is still limited.
Bacterial diseases
In a region with a brown rot history and where low levels of infection have to be accepted, roguing brown rot plants is applied as one of the measures, to keep the disease at such low levels. Also the plants, neighbouring the diseased plants, should not be used as seed.