All flats, pots and other equipment you use from year
to year should be disinfected after each use. Thorough
cleaning with a one part
chlorine bleach to nine parts
water solution will kill most of the spores.
Also, always use a sterile seeding medium. Although
using garden soil is not recommended, if you must use
it, be sure to sterilize it first. This involves heating
it to a high temperature and, if done in the house, can
cause an odor problem.
An easier and more effective way is to use commercial
vermiculite for starting
seedlings. These materials come sterilized in the bag
and have no fungal spores in them.