October 2002

Fungicides on the Horizon By A.R. Chase

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

One of the more interesting aspects of the new products istheir diversity. They range from newer, better strobilurins (and their closerelatives) 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 seeornamental 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 Aliettefor the past 20 years. This is the only phosphorous acid product that is labeledas a fungicide that I am aware of in this country — at least on ornamentaldiseases. At present, many local manufacturers and distributors have their ownversion of “Phos-acid” products, but they are registered asfertilizers or growth promoters. In the next 12-24 months this is due tochange.

The Newcomers

In a downy mildew trial last spring, we saw excellentcontrol on pansies with two Phos-acid alternatives, although one of them causedsignificant damage to the pansies. Aliette was effective and safe. One bigdifference between Aliette and some of the “fertilizers” is thepresence of aluminum. Without side-by-side comparisons, we cannot be sure thealternatives will work the same way as Aliette. I am looking forward to thesetrials for Pythium, Phytophthora and downy mildew.

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

Some of the new products I listed in the efficacy table areContrast, 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 wehad in ornamentals) that is very good for powdery mildew. Our trials this pastyear show some control of Alternaria leaf spot, downy mildew and rust. We alsohave been testing Fungo (thiophanate methyl like 3336) and Truban (etridiazolelike Terrazole). Finally, I decided to include some recent testing onHurricane. This product is a combination of active ingredients from Subdue Maxx(mefenoxam) and Medallion (fludioxinil). It works exactly the way one would expectsuch a combination to work.

I am starting to get excited about a couple of newbactericides, too. Neither is currently labeled for ornamentals but they havebeen promising in our early trials. One is a biological agent (Bacillussubtilis — Rhapsody from Agraquest) and the other is an SAR (Actigard fromSyngenta). SAR is “systemic acquired resistance” and acts by alertingthe plants’ defense systems before the pathogen attacks it. We have seen up to98 percent prevention of bacterial diseases and similar results on powderymildew when Actigard is used. Rhapsody has been shown to be effective againstpowdery mildew in trials by other researchers. The results on Pseudomonas leafspot on impatiens and delphinium were very good. One or both of these products wouldgive us a real shot at a rotation for bacterial disease control.

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

Awaiting the EPA

I am on a mission to find a really effective product forFusarium 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. Whenconditions are ideal, nothing stops these pathogens. We are still waiting forregistration of dimethomorph (Stature DM) from SePRO. This new activeingredient is excellent on Phytophthora root rot. It is combined with mancozebin a currently registered product from SePRO (Stature). Unfortunately, Staturecannot be drenched due to the mancozeb component so we will have to wait forStature DM.

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

So I think the overall news for disease control inornamentals is improving every year. We have more tools at our fingertips thanever before. They are diverse in their efficacy, plant, human and environmentalsafety and even in their cost of use. Since the stock market, the weather andalmost everything else is not cooperating, having so many choices is a realbreak.

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Editor’s Note: The use of specific trade names in thispublication does not constitute endorsement of these products in preference toothers containing the same active ingredients. The use of trade names is solelyfor the purpose of providing specific information and does not signify thatthey are approved to the exclusion of others. Mention of a product does notconstitute a guarantee or warranty of the product by the author or magazine.