Fungicides on the Horizon

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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