In general, there's no substitute for cleanliness in your growing space for
avoiding infestations. (And being careful about not introducing insects on
your clothes, etc from the outside environment). However, when the inevitable
happens, we've found the following to be effective, with differing cost to the
1) for aphids, Malathion works well with little damage to plants;
2) for thrips and black flies, Orthene or Resmethrin (by Ortho) -- both are
organophosphates, not good for humans, and young plants and new growth take a
beating; However, we have been successful in eliminating thrips (our most
devestating pest) following 2 or 3 sequential sprayings (about 5-7 d apart),
and most established plants survived; These compounds require a license to use
and you should see your greenhouse person for help with them.
We have tried Safer soaps (a detergent-type insecticide) to control aphids, and
manage to keep them down but not out with these substances.
Concerning fungicides, we have not resorted to using these on plants in
soil. Avoiding over-watering and allowing surface of soil to partilly dry out
between waterings generally avoids establishment of fungal growth on the soil.
(Be sure to allow air circulation over soil, and don't completely cover pots or
flats of plants except when you are first establishing them in soil after
transfer from a 100% humidity environment [e.g. tissue culture]). However,
benomyl (10mg/L) is an effective fungistatic agent for tissue or seedlings
grown on agar and we have not observed any adverse effect on Arabidopsis.
If you are having a problem with a specific insect, you will do best to
identify it first before seeking a remedy.
Good luck, George Karlin-Neumann