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05-08-2003, 11:42 PM

(Jerome) wrote:

Hello,

We purchased 5 variegated red twig dogwoods (approx. 2 to 3 ft tall)
about a month ago and planted them. In the last few weeks we have
noticed
black spots on most of the leaves for all 5 plants. We purchased a
fungicide at the advice of the nursery where we purchased them and
applied
it. It seems to have helped a bit however we have lost plenty of
leaves
and there are still blackspotsspots galore. On one of the 5 plants
2 of the leaves have a purplish color? We live in upstate NY (near
Syracuse)
and the temps have been mid 70's to 80's since we planted them. We
have
been watering them and thought perhaps too much, however the nursery
owner
said "you can never over-water dogwoods" so we ruled out overwatering.

Any advice on what causes these blackspots and caring for them would
be appreciated. Are these plants in danger or can they be saved/cured?

Thanks!

I didn't even know redtwig could get blackspot. They do get powdery
mildew, & that can indeed be worsened by too much dampness which wouldn't
otherwise be anything but dandy for a redtwig. Fungicides do not fix
leaves once they are infected; those have to be removed &discarded in such
a manner that they don't spread the fungus (like burned, or wrapped in
plastic & tossed in trashcan, not composted). If you let the leaves fall
to the ground & remain, then next year the spoors will jump up on the
shrubs all over again. Rigorous removal & clean-up of infected leaves will
be much mroe beneficial than fungicides, which shouldn't be necessary at
all if it's really only blackspot.

If it gets really bad you can cut redtwig nearly to the ground & it'll
grow back fresh. Overwatering isn't likely to happen with redtwig, but if
the shrubs are in perfectly draining soil, they could actually be
UNDERwatered even if you get to them regularly. WIth brand new plantings,
watering might not be getting in close enough to the as-yet short roots,
or water is draining through too rapidly & the roots are dry within an
hour, so the shrubs become too easily heat-stressed & drought-stressed
hence susceptible to diseases they wouldn't ordinarily get. And in that
case they will be much stronger next year when it gets more roots set out.

If the spots look too worrisome you might consider contacting a plant
pathology lab (your nearest major university likely has a horiticultural
extension, and someone there could point you to a lab that diagnose plant
diseases for gardeners). It might be something nastier than blackspot
that does need some aggressive treatment. Dogwood anthracnose (a
death-sentence disease) does not afflict redtwig dogwood, but anthracnose
has in the last couple years been observed jumping species, and will be
found on increasing kinds of shrubs & trees in the future, alas. What a
bitter thing it would be if you were one of the first to see the
relatively short leap from flowering dogwoods to redtwigs.

But accepting that it's "just" blackspot, the other things to do is check
out all rose-family shrubs growing too close by, prune to increase air
circulation, clean up all fallen leaves & discard those completely, &
starting late winter before spring spooring takes flight, spray the ground
around the base of the shrubs with horticultural oil or neem oil, which
pastes the spoors to the ground where they can do no harm. I'm in general
no great fan of needlessly expensive & overly faddish "garden teas" -- but
where mild funguses are concerned, use of those teas can shift the
microorganism mix in the soil in a healthy direction so that useful
microorganisms can better out-compete spoors of harmful funguses.

-paghat the ratgirl

--
"Of what are you afraid, my child?" inquired the kindly teacher.
"Oh, sir! The flowers, they are wild," replied the timid creature.
-from Peter Newell's "Wild Flowers"
See the Garden of Paghat the Ratgirl: http://www.paghat.com/