dry rot/gnats
Johannes Ulrich Urban (Wed, 15 Jun 2016 14:44:20 PDT)

Hello Monica,

Thank you for your reply. I think you problem is different from mine but
maybe this helps:

The term 'gnats' is difficult to translate for me, I looked it up and
maybe it is comparable to an infection with Euopean Sciaridae insects.
One variant of these tiny insects causes damage in moist conditions, the
larvae feed on tender roots and destroy seedlings this way. In seed
trays or propagators they find the right conditions: moist and warm. In
the past they used to be treated with insecticides but with little
success, mainly due to quickly developing resistance.
We now treat them with Steinernemia feltiae nematodes or Bacillus
thuringensis israelensis. I tried the nematodes with very good result
but not the Bacillus. I use the Bacillus on all kinds of caterpillars
with excellent results. Both are not harmful to humans or pets or useful
insects and are certified for ecological agriculture and are available
commercially in Europe.
Some of the 'gnats' are also part of the Sciaridae family so maybe these
treatments might also work for you.

I will further consider Dylan's advice on checking the compost moisture
of stored dormant tubers next winter. Maybe it is a fungus that enters
the tubers before they go dormant, Begonias have lots of fleshy stems
that often turn into a mush when the plant goes dormant. The plants shed
these dying shoots but maybe the damaging agent is already in the tuber
before the shoot is shed.

Thank your for your advice and ideas about this topic

Uli.