Subject: Re: Organic treatment for black spot on roses
From: "Bill Robinson" <roseguy@flash.net>
Organization:
Date: Tue, 20 Oct 98 15:47:42
Message-ID: <MOD$981020.20862@rec.gardens.ecosystems>
Perplexed in Ma Lisa asks about an organic way to prevent black spot on
roses.
Rose's resistance to black spot is a function of the rose's genetic make up.
There are some roses that
get black spot easily, some are highly disease resistant and there are some
that are virtually - if not actually, immune. The best organic way to
prevent black spot is to plant only disease resistant varieties.
I think most gardeners select roses on the basis of their beauty in some
terrific but distant garden. Just because a rose does great in New England
doesn't mean that it will do well in Texas and vice versa. Select roses that
you know do well in your area and that you know are disease resistant in
your conditions. If the rose that you selected and planted doesn't give good
performance and is prone to disease, take it out and keep it from infecting
others.
Step #2 When you prune your roses, be sure that you rake up all of the plant
debris, wash the pruned plant with a strong blast of water from the hose,
put down a good thick and clean layer of compost as a mulch to serve as a
barrier between the soil and your cleaned plant, and spray with a dormant
spray oil like Sun Oil or Eco-Oil. This will get your garden off to a clean
start.
Keep in mind that the organisms that cause black spot overwinter in the soil
and become established on the plant by being spashed up by water.
Step #3. Keep in mind that the fungus organisms that cause black spot need a
wet surface to become established and also to thrive. Keep the foliage as
dry as possible which can also mean keep the area open so there will be good
air circulation to help keep the foliage dry. This may mean making sure that
you plant your roses in a spot that has good air circulation and that also
has a good watering system that won't splash up on the foliage.
Step #4 If you have multiple roses and one of the roses comes down with
black spot, you can strip off the infected foliage, rake up and get rid of
the infected plant debris and infected mulch, wash again with the hose, add
a fresh new layer of clean compost as a mulch, and again spray with your
dormant spray oil.
Most of the fungicides are only effective in preventing infections and
ineffective in treating an established infection. Lime-sulfur is an
exception and is allowed for use in most certifying organic programs.
Lime-sulfur works as both a preventive and a corrective
control material.
Careful plant selection, keeping things clean, and keeping things dry are
very much more effective.
Bill
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