Re: roses
Monarch wrote:
>
> So far I haven't resorted to using commercial fungicides on my roses
> here in hot, steamy, south Texas.
> Right now I am using milk on the worst cases, one part milk (skim or
> whole) to four parts water. It does seem to help, doesn't kill
> beneficial insects, and adds calcium and nutrients to the plants and
> soil.
Hi
I haven't seen mildew on roses for years, but ages ago I overcame it
with the baking soda/ oil spray, which I have found to work well for
that fungus wherever it appears.
Having seen several enthusiastic recommendations on the Organic
Gardening List I have tried the milk treatment on several cases of
mildew on various plants this (southern) summer, but am not very
impressed, as I doesn't seem to have been nearly as effective as the
soda treatment, which I am now going to return to, even if it is a bit
more trouble to prepare than diluting milk..
>
> In the past I was careful not to get the leaves wet while watering,
> always doing it by hand or soaker hoses, never get them wet before dark,
> and all that stuff. Well, I have found that washing the roses each time
> I water them works better than all of the above. I hit them with the
> hose as forcefully as I can. If using a sprinkler, I leave it on a fine
> mist all night. Hosing off has reduced black spot and mildew much more
> than anything else I have tried and sure saves a lot of time.
Many experimenters would agree with you I think. One of the major aims
of plant protection is simply to prevent disease spores which land on
leaves actually getting a hold. This can sometimes be done by having
other harmless organisms present which block access to the leaf surface
and this is the basis of using protective sprays like compost tea which
often have no actual fungicidal action.
On the other hand vigorous washing or a constant misting for may hours
can as you suggest simply wash disease spores off, which will be equally
effective. I think however one has to be careful there is enough water
to really swill the spores off the foliage, otherwise a mere dampness on
the leaves is most likely to encourage spore germination and subsequent
infection.
I haven't managed to get rid of black spot in my garden, but it has
become much less of a problem where suceptible roses have been
generously fed (with compost and animal manure pellets) watered and
mulched (both to maintain regular moisture at the roots and also to
cover and rot any diseased leaves falling to the ground to discourage
re-infection).
Rust is a much easier proposition if one can be diligent for a few weeks
in spring after the new leaves unfold. Rust fungi are most unusual in
that many species do not have just one or two kinds of spore, but even
more. Rose Rust has four active ones.
(1)The summer spores are what most people are familiar with and they are
bright orange. Yhey grow in clusters (sori) on the underside of the
leaves each clump being marked on the upper surface by a yellow
spot.These spores are freely shed and spread the disease to new young
leaves as these appear.
(2) Towards the end of the season the sori begin to produce a second
type of spores which are dark blackish-brown in colour. These are
thick-walled overwintering spores which resist cold and they cling to
the leaves when they are shed and do not germinate until spring.
Removing and destroying fallen leaves or by burying them under plenty of
compost and mulch so that they quickly rot away will greatly reduce
future infections.
(3)On any leaves with winter spores which have not been destroyed by
spring and are not too deeply buried the spores will begin to germinate
about the time the roses get their new leaves. What they produce is a
small colourless shoot with four cells each of which gives rise to a
single colourless spore.
(4) These colourless spores get up on to the surfaces of the new rose
leaves by air currents or water splash and germinate to give rise to
yet another spore type. Unlike the summer spores. these are produced on
the upper leaf surface or sometimes on the petioles, and the fruiting
bodies are bright orange-red and perfectly visible to the naked eye.
Under a magnifying glass it is easy to see they are in the form of a
tiny spore-filled cup, which gives the stage its name of Cluster Cups.
Unlike the summer sori they are quite few in number, often only one or
two on each of a very few leaves near the base of the bush. If left to
develop they will then give rise to stage (1) and start the infection
all over again, but they are a real weak link as they are pretty easy to
deal with by just taking off and destroying the infected leaves.
If you have been assidious in removing or deep covering least year's
leaves you may not see them at all and then there will be no summer
rust, but even if some do appear because they are so bright and easily
spotted and so few in number it is quite feasible to spot and remove
them as soon as they appear. If you mannge to get the lot you will not
see rust again that year - maybe never again if there are no other rose
gardens very near you and no newly-purchased bush brings more in.
One thing which makes this treatmet feasable even if you have a lot of
roses is that quite a few varieties are resistant and never, or scarcely
ever, get rust at all, so all you have to watch are the susceptible
kinds. It's little good my trying to tell you susceptible varieties as
they do vary somewhat from place to place, probably because the rust
occurs in different strains, but many but not all, pink and red roses
are affected and most, but not all, yellow and white roses are
resistant. A few, like the old variety Queen Elizabeth are so horribly
sucseptible it is very difficult to clean them up and they may need the
shovel treatment. but most can be cleared as I suggest.
Moira
--
Tony & Moira Ryan <theryans@xtra.co.nz>
Wainuiomata (near Wellington, capital city of New Zealand)
