I didn't know you could spray a pre emergence on ginseng. That is interesting to know that it did not hurt the ginseng but kills the weeds. I know weeds typically come up before ginseng and many spray in the early spring after the weeds are up but before the ginseng comes up.
Sorry i should have been more specific. I meant to say that i sprayed my ginseng with fungicide before they came up and seemed to have better results. I was wondering when i should spray again now that it is up.
Wildgrower, this will depend on a number of factors. As Latt said, rain is one of them. You can spray for weeds pre-emergent, but that's sometimes risky.
I often spray a strong copper fungicide (Kocide) pre-emergent or just after emergence.
However, if you are going to use fungicides, it is very important that you use several of them and do not spray the same one back to back and never ever more than twice in a row. This will cause resistance to that particular fungicide and the result will be the complete ineffectiveness of that particular type of fungicide. There are not many out there we can use on ginseng, so we need to be very careful to not lose the effectiveness of any of them.
If I spray copper early, I will often go back after emergence with Ridomil. If it is rainy, I might use Dithane instead for the next application. Dithane forms a protective covering on the plant surface and prevents the fungi spores from inoculating the plant tissue. After that, I normally wait to see how the summer begins to develop. If there are disease issues, I'll spray for that particular disease and sometimes that means I'll have to spray every two weeks for the rest of the summer. Other years, I won't have to spray at all again after that second application depending on the weather and situation in the beds.