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Southern Blight/past postings/Solberg/Millhorn/Gleason/Nelson


Bob Solberg wrote: (10/29/97)

----- Original Message -----
From: Green Hill Farm, Inc. <greenhill@theonramp.net>
To: <hosta-l@honza.com>
Cc: <greenhill@theonramp.net>
Sent: Wednesday, October 29, 1997 12:32 PM
Subject: Pest problems 2


Just a few more comments:
Southern Blight: This fungus pest is very persistant in the soil so a
persistant fungicide is recommended, or several applications of of a
less
persistant one. Terrachlor if you can get it works well as it is
persistant. 10% Bleach works also in quantity as a drench.
Try applying the fungicide in anticipation of the problem next
year.Treat
areas where it appeared this year as soon as the hot dry weather of late
June in the South or July in the Midwest begins. Remember it is soil
borne
not in the plants and drench the area well.
Also I have seen some correlation between using hardwood bark mulches
and
the occurance of this disease in this area. I would think especially
mulches that are from ground stumps may be more of a problem.

Spots: Most round or oval brown spots are the result of fungus
infections.
They are usually secondary fungus infections or areas of dead or
stressed
tissue that fungus invade. (Healthy hostas that are active growing are
not
as open to these fungi.)
Numerous tiny brown spots, like pin punctures, usually early in the
season
are the result of aphids. Aphids can be a problem if cool damp weather
persists in the spring or on plants grown in hoop houses or under frost
cloth. The numerous punctures made by the sucking mouth parts of the
aphids
can later become infected with fungus. This fungus can then be spread to
healthy plants through the sap in their mouths. A systemic pesticide
like
Orthene will kill the aphids in one spraying. Insecticidal soaps work
also
but may need to applied more than once. Usually warmer weather and good
air
circulation will limit aphid populations later in the year. Any
fungicide
like Daconyl will slow the fungus.

Hostas that are heat dormant or are stressed due to lack of water or
nutritional deficiencies in mid-summer may develope red spots. These are
a
secondary anthracnose infection and are more pronounced on gold hostas
especially 'Tokudama' types but are present on green and blue hostas
also.
Again a systemic fungicide will help control the spread of the fungus
but
not make the spots go away. Good cultural practices, (regular
irrigation,
maintaining adequate nitrogen levels throughout the summer, and keeping
the
plants cool buy overhead watering or shading them), may decrease this
pest
problem.

Unlike Southern Blight, none of these fungus problems are persistant.
Good
fall garden cleanup of old foliage may reduce the number fungus spores
in
the area but the seceptability of certain hostas (ie. 'Tokudamas') to
infection maybe genetically based.

=============================================
Professor Mark Gleason wrote:(7/26/98)

Mr. Nelson,

Thanks for your inquiry.

Terraclor 75 WP and Terraclor 400 both have very broad ornamental
labels, and specify control of Sclerotium rolfsii, but do not specify
hosta among the many crops on the labels. However, wording on the label
encourages users to try Terraclor on ornamentals not covered on the
label - but on an experimental basis, on a few plants rather than an
entire crop.

A key step is working out a use rate that is effective on hostas but not
phytotoxic to them. Another step is to decide on when to apply the
fungicide to hosta: As a soak treatment to bare or potted crowns befroe
transplanting? As a drench after transplanting? Clearly it must be
applied to the root zone, since this is where the fungus attacks the
plant. You may wish to consult with your friend who has had success
against Southern blight using Terraclor.

I am a bit surprised that hosta is not on the Terraclor label, given
hosta's popularity and the problems Southern blight is causing for
growers. I will talk to a Uniroyal rep and get his opinion on the issue.

I believe that Benlate is no longer labeled for use on herbaceous
ornamentals due to major lawsuit problems several years ago. The
Cleary's 3336 label does not claim control of S. rolfsii, but another
product from the same company, called Defend 2F, does claim control of
this pathogen on iris (again, hosta is not specified). Defend 2F has the
same active ingredient as Terraclor - PCNB, or pentachloronitrobenzene -
and the label looks very similar to that for Terraclor. So you have 2
product options, even though their chemistry is identical and neither
specifies hosta.

Are these products legal to use on hosta? Yes, in my opinion, due to the
inclusive way in which the label is written. As I said, it's up to the
user to work out effective use rates and methodologies on crops that
aren't specified on the label.

I'm not a font of knowledge on hosta crown rot, but it would seem to be
an interesting subject for study. Three of the biggest questions in my
mind are:

1) How does resistance vary among hosta varieties?

2) How effective are various fungicide use strategies against the
disease?

3) How does the growing environment affect disease risk, and how can we
manipulate it to reduce the risk?

There are several good subjects for M.S. or Ph.D. degrees buried in
those questions! The best individuals to work on these questions are
pathologists already heavily involved in the ornamentals area - for
example, Austin Hagan at Auburn, Steve Jeffers at Clemson, Mary Hausbeck
at Michigan State. Gary Moorman at Penn State, or Marge Daughtrey at
Cornell. If you want to pursue this issue further, I can provide emails
for eny or all of these people.

Best regards,
Mark Gleason
Professor/Extension Plant Pathologist
================================================
Hank Millhorn wrote:(1/9/98)
Greetings All -
Seems as if crown rot, what with the weather and all, is the topic du
jour.
Here in good ole mid zone 6 we find the systemic fungicide Benlate aka
benomyl a good prophylactic treatment, as well an acute treatment as in
'ohmahgoddd' did you notice we've got crown rot on, ___________ ????!!!!
It's also good to prevent damp off from from getting started in the
first place in the seeding patch.  As a systemic it is absorbed into the
living tissue and lasts good while.
It used to be commonly available, we got our supply last years from
Jungs in Wisconsin.
Hank
=============================================
Dan Nelson writes:(6/15/99)
I put small wire flags at my 15 or so hostas that suffered from Southern
Blight last year. This year I have applied Terraclor BEFORE Southern
Blight has shown it ugly face. Fungicides are best applied as a
preventitive before disease occurs. When southern blight is noticed on
hostas much of the damage has already occured. I will see this year if
the same hostas suffer from southern blight. It is important to mark
treated hostas. This disease needs treating for several years as the
spores (sclerotia) last for years in a dormant stage. These spores are
mustard seed in size and look like a granular fertilizer. Once you learn
to recognize the spores of southern blight positive I.D. is easy.

Southern Blight is a major agricultural disease in the south. Some crops
such as peanuts are treated every year as a preventive.

Dan Nelson


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