Mancozeb is a preventative like previously said. A good rule of thumb
is that you will lose 1/2 of the spray for every inch of rain you
recieve. Mancozeb also spreads with rain so sometimes rain can help
coverage. It needs to be dry before the rain and "usually" that calls
for the spray to be on at least 2 hours BEFORE the rain. I also spray
it every 10 days whether it rains or not because of dew. Systemic like
Nova are soaked in to the plant unlike mancozeb/penncozeb/dithane
which lays on top of the leaf. Mancozeb will not kill an infection
like a systemic can it just prevents it from spreading.

Hope this helps.


Bob


"Paul E. Lehmann" > wrote in message >...
> Ken Anderson wrote:
>
> > "Brad B." > wrote in message
> >>
> >> My understanding is that Mancozeb is a preventive and will not kill an
> >> existing infection.
> >>
> >>
> > If that's true, then the Mancozeb needs to be on the plant when and if a
> > spore
> > lands on it. Once it's washed off, it would have zero effectiveness.
> > Sounds believeable to me.
> > Ken
>
> I believe Mancozeb - Penncozeb will ramain to some extent after a rain. A
> lot depends on the amount of rain and the length of time it rains. I
> believe that if the fungicide is on for several hours prior to a rain, some
> of it will remain after a light rain. You might just look at the leaves
> after a rain and see if there is any spray residue on them. My
> understanding also is that Mancozeb - Penncozeb will not kill an existing
> infection. You will need a systemic fungicide to do this and they are
> expensive. Prevention is the best route.