I think the \"real\" problem is that you are trying to grow ginseng in large beds and perhaps to densely populated.
I did the same thing when I started out. I made a lot of beds 5'x50' or larger... and put the seeds down 4-5 per sq ft. I had great germination, and some densely populated beds and the seedlings looked great initially...
But then after a few good rains in May and early June I checked them and the old yellow spot was showing up, then later on the leaves looked like they were melting.
I am not the type to spray chemicals, so I modified my planting methods and now only print small patches (say 4'x 4') and may only put a dozen seeds in that space, and I space the beds out quite a bit too. The beds I have planted like that - no problem, they have done very well with very few casualties.
The large densely populated beds I planted, thinned out a lot over the years, only a fraction of those still remain, but they are doing well now too, with much less sign of disease issues.
I think it is just a fact that if you are going to plant large beds and 4-5 seeds per sq ft... you are going to have to spray chemicals on a regular basis to get the majority of those to survive.
Myself... I would rather not spray chemicals, and instead just plant seeds at a much more natural rate, and give them the space they need to remain disease free naturally.
I can't advise at all on what you need to spray or when, sorry about that.
But good luck to you on finding the right way to grow ginseng in your area, and with matching that up with your commitment to work the stuff as it needs to be worked.