Re: dogwood disease
- Subject: [cg] Re: dogwood disease
- From: Don Boekelheide firstname.lastname@example.org
- Date: Sat, 23 Nov 2002 22:01:05 -0800 (PST)
The fungus that causes dogwood anthracnose spreads
from sick trees in the spring, via spores carried by
splashing rain, and possibly insects, birds and
people. It is probably not such a good idea to go dig
up 'free' dogwoods in the woods anymore. It's a 'new'
disease, not clearly identified until the early 1990s.
To keep your dogwoods from getting it, first of all
keep them healthy. Plant them in soil well supplied
with organic matter, ideally good 'living' compost. Be
sure to mulch around the base (but not right next to
the trunk, remember mulch like a bagel, not like a
volcano), no deeper than 3-4 in (less than 10 cm).
Water regularly during dry periods using drip or
watering at the base, not overhead sprinking. Shady
wet conditions favor the disease, so try to keep the
trees 'open' to light and air even if they are under
bigger trees. Fertilize with compost, stay away from
high nitrogen fertilizers. Be careful to keep mowers
and trimmers away from the trees (all trees). Keep
leaves raked up in the fall. Remove dead limbs before
the disease reaches the trunk and - especially - any
brown leaves that hang on the tree through winter. My
suggestion is to keep any such material from sick
plants out of your home or garden compost pile.
Though tree health is the most important defense, you
can choose to apply a fungicide in the spring at bud
break, continuing for about a month. Organic options
include Bordeaux mix (see a recipe, it's copper
sulfate solution, essentially) or one of the
commercial organic 'biological' interference agents
which offer a mix of natural fungicidal agents and
bacteria. Compost teas might also work, as a spray.
Non-organic fungicide options include mancozeb, among
others - call coop extension for chemical advice, but
stay away from systemics anywhere near food crops.
You can pick resistant types of dogwood, but not all
dogwoods are the same. Kousa dogwood (Cornus kousa) is
a Korean dogwood. It's a pretty tree, but not at all
the same as American (flowering) dogwood (Cornus
florida). Kousas look to me almost like a doublefile
viburnum when they flower, at least a month after
local dogwoods down here in zone 7. There are some
kousa x florida crosses, such as the 'Stellar'
hybrids. More interesting to me are American dogwood
varieties that have been developed from resistant
plants, such as 'Appalachian Spring'.
As Denise says, other native trees make good choices
for gardens. Redbuds (Cercis canadiensus, I
think)certainly are nice. One favorite of mine is
'Forest Pansy', with purplish leaves in the spring,
like an ornamental plum tree.
Good luck, So far, I've seen no sign of the disease
locally, but I know people who've seen it. It's not
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