Potatoes - More on Blackleg
This is a bacterial rot, and there's not much one can do about it. Gardeners do not use bacterial sprays.
The infection often comes from the seed tuber. The underground part of the stem turns black and starts to rot. This spreads up the stem, the plant turns yellow and then collapses.
The infection can occur on any variety but is more common in earlies. Cold conditions seem to encourage the infection.
The only treatment for the gardener is to remove and destroy infected stems as cleanly and rapidly as possible. Also don't plant blemished seed. It may be infected already.
Nigel Deacon / Diversity website
