Insect Pests on Over-Wintering Dahlia Tubers

Slugs, earwigs (pictured) and wireworms are all serious pests which can over-winter with stored dahlia tubers. Of these, I have found wireworms to cause the worst damage, since they attack the necks and render the tubers useless; the other two attack the young plants during the next growing season.

Although I have never stored tubers individually, complete removal of soil and a thorough washing is obviously ideal for removing pests, along with their eggs. If the pest problem is severe, this might justify the increased risk of loss of tubers through disease (especially if tubers were dusted with sulphur powder).

So far, this has not proved necessary. I have found a dusting with "Derris" dust ('0.2% w/w rotenone') effective against wireworms. The others are removed with the soil just prior to planting. Though, to be honest, I haven't really had a problem with earwigs before. It might be worth spraying tubers with 'Provado Vine Weevil Killer' (9g/l 'thiacloprid') at some stage.