Re: Rust on roses

Janet Smithen wrote:
> 
> Hello Melissa,
> 
>     Eden in a beautiful rose (real name: Pierre de Ronsard) but in my
> experience, it is one that is particularly suseptable to rust. The
> organic method for its treatment is to strip all the leaves from the
> plant and clean up the leaves and mulch under it. Send all this to the
> dump; not to your compost. Now spray the bare canes with light
> horticultural oil.
>     New leaves will soon regrow. Watch carefully for those tell-tale
> orange spots and pick off any leaves on which they appear. If your plant
> can be moved to a spot with more air circulation (even windy) you will
> have less trouble with rust.
> For more good information on managing roses organically, visit our
> Victorian Rose Garden web site listed below.

Just a couple of small points to add to Jan's competant recommendations.

Melissa was speculating whether her use of insecticidal soap had some
part in the attack. No Melissa, the rust appearing after you had used
the soap was purely coincidental.

Secondly, a control method I have found very successful in my own garden
with roses susceptible to rust. It can only be done at the appropriate
time of year and depends on a peculiarity of the rose rust's lifecycle.
Bear with me if I describe this in some detail. 

If any infected leaves survive until autumn, falling temperatures cause
a second type of spore to be produced which is deep blackish-brown. The
pustules can be clearly see on the leaves either on their own or mixed
with the orange summer ones. The orange summer spores are thin walled
and do not usually survive through winter, but the dark spores are much
tougher due to much thicker walls. When these spores fall to the ground
they remain dormant until the roses start to leaf in spring and then
each grows out a short stalk which bears four colourless spores. These
spores  reach the new rose leaves with wind or watersplash and cause yet
another type of infection. This latter takes the form of bright
orange-red cup-shaped pustules on the TOP of the new leaves or
occasionally on the petioles (leafstalks) The spores from the cluster
cup stage (as this is known) the infect further leaves producing the
usual mass of orange summer spores.

The cluster-cups are never produced in big numbers, so this forms a
bottleneck in the rust's life history. They usually seem to appear as
soon as the rose leaves are fully unfurled and the danger period
probably lasts over about a month (as my seasons are reversed, I can't
suggest actual dates).

If you have a rose which you know is susceptible to rust (not all roses
are). I suggest you look over the new leaves carefully once or twice a
week for some time for the cluster-cups. The are not difficult to spot.
Generally about three to five occur on one leaf and they are bright
orange-red and about pinhead size. Infections most commonly occur on
leaves near to the ground, which I guess is to be expected, as the
colourless spore stage is produced at ground level. It is rare for more
than half a dozen leaves on one bush to be infected, sometimes it is
only a single leaf and occasionally just one pustule. 

The point of describing this stage in such detail is that if the
infected leaves are quickly removed and destroyed at theis stage
commonly no summer infection will occur that year and even for many
years afterwards (Unless, of course the rose is unlucky enough to be
surrounded with untreated susceptible companions from which new
infections by summer spores can spread).

I used this with great effect years ago on Sarah van Fleet, a hybrid
between a rust-immune Rugosa and a suceptible hybrid tea, which was a
real martyr to rust. Without this method, I think I would have abandoned
this variety as hopeless.

Moira
-- 
Tony & Moira Ryan <theryans@xtra.co.nz>
Wainuiomata, New Zealand. (on the "Ring of Fire" in the SW Pacific).
Lat. 41:16S Long. 174:58E. Climate: Mediterranean/Temperate
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