Help. One of my a. triphyllums is sick.

[Jim McClements, Dover, DE z6]

Jaime

I'm going to copy below four postings from August about Arisaema rust, so
that all can be refreshed on the subject. There doesn't seem to be any
disagreement about the diagnosis!

Jim McClements


>From Paul Christian:

Hi All,

As far as I am aware, rusts are host specific.  We are not talking of just
rust, we are as an example, talking of Hollyhock Rust, Arisaema rust etc. If
your Hollyhocks are 'rusty' your Arisaemas will not fall to it, as it is
Hollyhock rust.

The second thing about (?most/all?) rusts is that they actually need TWO
hosts to complete their life cycle, they have a phase on each host
alternately.  If one host is missing then the other will not fall to rust.
To take this further eliminate one host and the infection on the second will
not come about. This was the thinking behind the attempt in the US to
eliminate berberis as it is a secondary host of a rust that afflicts one of
the major food crops, wheat I think, but it is perhaps not important.  The
attempt failed but it was politically inspired and half-baked, rather than
powered by a full scientific study.

It may be that in parts of the US or Canada, that the other host for the
Arisaema rust is missing, so Rand could find that his Areisaemas appeared to
immune to rust, Jim's might not be.

This by the way is old back of the brain botany, I hope I am not wildly out
with modern thinking !

Treatment, don't know BUT. I have annual infections here on Dactylorhiza
incarnata (an marsh orchid), the secondary host is willow, normally I guess
Salix repens, with which it is usually associated in the wild strange to
say. I treated this year by hand picking of obvious infection as soon as
some was noticed, and then dunking of the living plants in a x4 strength
solution of Benlate (Benomyl), mixed with x4 strength Supercarb
(carnbendazim plus activator).  2 hours at room temperature.

I have dead areas of leaves but NO infection, not a trace. I put the dead
leaf areas down to areas infected and perhaps killed, but in which the
infection itself has vanished.  This may be Doc Christians coloured Medicine
Water, I dont know.  I would stress that this may not be a cure, I have only
one year's results, but at the same time I have no rust at all whatsoever -
period. full stop.

my intended two pennyworth (2c) must be at least a pound now ($1.63 !) I
will shut up

Cheers
Paul :-))


Two from Doug Green:

To further follow up on this rust discussion. I've asked the Florinet
extension group list to comment on the use of Benlate at 4X and Cygon as
possible rust control agents. I'll also ask them for their comments on
anything they may have heard. I'll get back to you with any data they
provide.

Doug.

Some time ago, there was a thread on rust and I said I would check out the
extension folks over at Florinet and see what they had to say about rust.
Between my trips this summer to conferences and an Irish garden tour, I've
not had a chance to get to the bottom of my desk, never mind the email
lineup.   This is the single comment I received on the query and I include
it for your interest.  I think it is important for those using chemicals
such as Benomyl or Cygon to clearly evaluate their problems and control
strategies.

"Systemic rusts are difficult. Plantvax has a generic label that
would cover this plant, I believe. Terraguard might work as well. These are
both systemics. Protect T/O as a barrier protectant might work on plants just
before cuttings are to be harvested.
I agree with the grower's sanitation efforts. Removing all sporulating
lesions from infected tissue before trying to take cuttings, etc. Benomyl
would be a waste of time. I have no information on the effects of Cygon. Who
knows? CPP"

Doug.


One from Scott Vergara:

Greetings All,

Just a few comments following Paul Christian's comments on Rust.
Yes, rusts are usually quite host specific.  This specificity may be at the
generic or species level, though many cultivars or natural ecotypes may
have some level of tolerance, resistance or immunity.  However the rust
fungi mutate readily forming many strains.  This provides workers in the
Wheat Rust Resistance Breeding programs in the US with job security.

Rust are extremely complicated as a group.  Some having as many as five
spore types infecting two different hosts (heteroecious types).  While
others (autoecious) have two to five spores on one host or only one known
spore type and a single host.

Arisaema rust is caused by Uromyces caladii which has 4 of the spore stages
and has been reported from NY to FL and TX and the Pacific Northwest.
(from the 5th ed. of Westcott's Plant Disease Handbook)

I do not know if there is an alternate host or not. Perhaps some plant
pathologist on the list or on Aroid-L might volunteer more information.

A word of caution. Rust spores are windborne, thus very small and
lightweight.  It has been reported in some species that the spores can
cling to tools, clothing, (hair?) so  those who tromp though infested areas
might not want to come home to their collections and go grubbing about
immediately.

As we bring more and more species together within the range of the pathogen
it may just be a matter of time before strains appear that may cause
serious problems.

Sorry for the gloomy outlook...we pathologist types tend to have a wet
blanket side to us.

Best Regards,
Scott