Re: Further Seaweed Theories
Tim Longville wrote:
> I read a piece recently by a UK pundit who suggested that spraying
> with seaweed solution might also have at least indirect benefits in
> relation to rust and blackspot, for which, said he, there are
> currently no organic remedies. The theory was that the seaweed spray
> might help simply by being a sort of plant vitamin pill - increased
> health = increased resistance to disease. (This was supported by a
> biologist working for Maxicrop - but, since they make seaweed
> solutions, they WOULD say that, wouldn't they...)
>
> Any comments anyone? (a) on the lack of organic remedies for rust and
> blackspot, (b) on the proposed benefits of seaweed spray in that
> situation.
Tim
The answer to a) is unfortunately pretty well correct.
Some protection against both types of fungus may be obtained by covering
the leaves with a spray of either copper or sulphur and in many
industrilized countries the sulphur content of the air, especially in
towns is enough to make black spot at least very uncommon. I remember
some rosarian(Graham Thomas maybe) bewailing in an old book how much
more trouble he had with black spot after moving from a town garden into
the depths of the country with its nice clean air (I said it was an _old_
book )
Both sulphur and copper are fairly freely used by some organic
practitioners, but there is concern that sulphur tends to have an
acidifying effect and also destroy some helpful insects while excess
copper can quite easily become a hazard to soil organisms including
earthworms, and many people would like to reduce their dependence on them
if possible.
As to b)., the idea of less hazardous leaf protectants has lead to
experiments with various organic solutions including manure and compost
"teas". The biggest success seems to have been with a tea made from
mature compost, which greatly reduces infections of such diseases as
apple scab, late blight of potatoes and soft rot of strawberries.
However, the experimenters agree this has no apparent effect on rusts and
when I tried it on roses I couldn't see any effect on the black spot
fungus either, although it certainly worked on the apple scab and my
last crop had almost no spotty "faces" at all. It also vastly reduced a
nasty fungus spot on my quince(Fabrea) in which it was more effective
than the recommended copper had ever been.
There have been interesting postings recently on the Organic list about
using seaweed spray as a protection against mild frosts. It seems that
tender leaves covered with the spray can withstand a few degrees of frost
without damage.
The mechanism is not really undestood, but may be related to the mucilage
present in such products. Perhaps when applied against disease there is
some similar mechanical effect of denying the spores access to the leaf
surface, as well as any tonic effect.
One thing which my observations have convinced me of is that plants in
perfect vigorous health (like very healthy people) have a marked
resistance to both fungus infections and insect attacks. One of the
hazards for many species is senescence, whic will quite often lead to
attacks. Two examples from my own garden are cabbage aphis only on old
brassicas left to flower for the bees and rust on antirrhinums right at
the end of the season. Though not protected in any way adjacent young
vigorously-growing plants have remained unaffected. Both these are of
course short-lived plants, but many longer-lived species become more
susceptible to disease as they leave the flush of youth and renewal by
propagation might certainly help.
Maxicrop is much less available here than it once was and my supply is
pretty old, but I now have a local product which seems to be comparable
and I will certainly give it a go this year.
Moira
--
Tony & Moira Ryan <theryans@xtra.co.nz>
Wainuiomata,
New Zealand (astride the "Ring of Fire" in the SW Pacific).
