I may be making a mistake, I'm just a beginner gardener.
We are living in France for the moment because my husband was sent to
work here for a couple of years. Reading French posts on
fr.rec.jardinage I noticed they use horsetail (Equisetum pratense -
prêle des près) macerated in water to spray again fungus infections
(powdery mildew, phytophtora).
Maybe a more experienced gardener could tell us if the plants, coming
from the same family, are very different and you can't use yours (at
least part of it) to spray when you will have a crop.
I have seen this "purin de prêle" also bottled and sold in stores as a
biodegradable treatment for crops.