Fungicides on the Horizon

November 5, 2002 - 13:47

It's only been in the last three months that we've started seeing more experimental products available for testing, and with that, we definitely have something to look forward to -- increased diversity.

It seems like only a short while ago since I was trying to
write this article for 2001. Now it is 2002, and I wonder what has changed in
the past 12 months. Although we have seen registrations for new fungicides
during the past couple of years, availability of experimental products for
development has been low. In the past three months, however, we have started
seeing a wide variety of products come into testing on ornamentals. Many of
these are a couple or more years away from registration, but at least there are
more in the pipeline.

One of the more interesting aspects of the new products is
their diversity. They range from newer, better strobilurins (and their close
relatives) to really old (from the 1960s) chemistry being tried in a new arena.
Some of the products are already registered on turf, and we should see
ornamental labels soon. For those that are not even registered in this country,
the wait may be longer, although everyone is looking for reduced-risk products,
and that significantly shortens the wait.

Another development is use of products described as
"fertilizer" for disease control. I have been working with Aliette
for the past 20 years. This is the only phosphorous acid product that is labeled
as a fungicide that I am aware of in this country -- at least on ornamental
diseases. At present, many local manufacturers and distributors have their own
version of "Phos-acid" products, but they are registered as
fertilizers or growth promoters. In the next 12-24 months this is due to
change.

The Newcomers

In a downy mildew trial last spring, we saw excellent
control on pansies with two Phos-acid alternatives, although one of them caused
significant damage to the pansies. Aliette was effective and safe. One big
difference between Aliette and some of the "fertilizers" is the
presence of aluminum. Without side-by-side comparisons, we cannot be sure the
alternatives will work the same way as Aliette. I am looking forward to these
trials for Pythium, Phytophthora and downy mildew.

I have updated the efficacy table that was printed in GPN's
December 2001 issue (see Table 1, right). One new addition is a new column for
Sclerotinia blight. Sclerotinia is gaining a real foothold on the West Coast,
especially in cut flowers, bedding plants and potted flowering crops. One of
the problems is that the disease is going uncontrolled until entire greenhouses
are contaminated with huge, black, ugly sclerotia. Using a fungicide at this
point may prove completely ineffective since eradicating sclerotia will be
almost impossible without use of methyl bromide or steam. We were lucky enough
to get three trials done on Sclerotinia blight on petunia this past
winter-spring and are hoping to do some this winter on Gerber daisies and
larkspur.

Some of the new products I listed in the efficacy table are
Contrast, Cygnus and Fungo. Contrast is primarily a Rhizoctonia compound,
although we have been hearing about very good control of Southern blight
(Sclerotium rolfsii) too. Cygnus is a strobilurin compound (the first one we
had in ornamentals) that is very good for powdery mildew. Our trials this past
year show some control of Alternaria leaf spot, downy mildew and rust. We also
have been testing Fungo (thiophanate methyl like 3336) and Truban (etridiazole
like Terrazole). Finally, I decided to include some recent testing on
Hurricane. This product is a combination of active ingredients from Subdue Maxx
(mefenoxam) and Medallion (fludioxinil). It works exactly the way one would expect
such a combination to work.

I am starting to get excited about a couple of new
bactericides, too. Neither is currently labeled for ornamentals but they have
been promising in our early trials. One is a biological agent (Bacillus
subtilis -- Rhapsody from Agraquest) and the other is an SAR (Actigard from
Syngenta). SAR is "systemic acquired resistance" and acts by alerting
the plants' defense systems before the pathogen attacks it. We have seen up to
98 percent prevention of bacterial diseases and similar results on powdery
mildew when Actigard is used. Rhapsody has been shown to be effective against
powdery mildew in trials by other researchers. The results on Pseudomonas leaf
spot on impatiens and delphinium were very good. One or both of these products would
give us a real shot at a rotation for bacterial disease control.

Camelot is a relatively new fungicide/bactericide effective
on a wide variety of diseases from the standard Pseudomonas leaf spot to
Alternaria leaf spot and powdery mildew. This year, we kept up our testing on
Pythium root rot as well. Our most recent trial showed excellent control with
soil drenches of Camelot at one or three pints per 100 gallons. This particular
Pythium on snapdragons is apparently resistant to Subdue Maxx and Aliette, as
both products failed in snapdragon trials for the second time this year. We
have found good results with Phyton 27 used as a drench for Pythium root rot as
well.

Awaiting the EPA

I am on a mission to find a really effective product for
Fusarium wilt in container ornamentals. Our best fungicides (Medallion,
Terraguard and Heritage) are not 100-percent effective on this deadly disease.
Another serious problem has been Phytophthora on many ornamentals. When
conditions are ideal, nothing stops these pathogens. We are still waiting for
registration of dimethomorph (Stature DM) from SePRO. This new active
ingredient is excellent on Phytophthora root rot. It is combined with mancozeb
in a currently registered product from SePRO (Stature). Unfortunately, Stature
cannot be drenched due to the mancozeb component so we will have to wait for
Stature DM.

Over the past year, I have been involved with the California
Cut Flower Commission as coordinator of its efforts to find a methyl bromide
replacement. By January 2005, we hope to have a number of products researched
and labeled for some of the serious and debilitating diseases on field-grown
cut flowers. While the loss of methyl bromide may not directly affect many
ornamental producers, it will change the face of cut flower production in
California and Florida, at the very least. Other industries that will be hurt
are the bulb crop producers (Caladiums in Florida) and anyone still using
natural soil as a component of their potting medium.

So I think the overall news for disease control in
ornamentals is improving every year. We have more tools at our fingertips than
ever before. They are diverse in their efficacy, plant, human and environmental
safety and even in their cost of use. Since the stock market, the weather and
almost everything else is not cooperating, having so many choices is a real
break.

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Editor's Note: The use of specific trade names in this
publication does not constitute endorsement of these products in preference to
others containing the same active ingredients. The use of trade names is solely
for the purpose of providing specific information and does not signify that
they are approved to the exclusion of others. Mention of a product does not
constitute a guarantee or warranty of the product by the author or magazine.

About The Author

Ann Chase is a plant pathologist and president of Chase Research Gardens Inc., Mt. Aukum, Calif. Further information on disease control is available at www.chaseresearchgardens.com.

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