2001 Product Efficacy Update: Disease Control On Ornamentals By A.R. Chase

For the past three years, I have been asked to review new disease control products for the ornamental industry. In 1999, I tried to list newer products and their activities, including the broad range of those products now available. In 2000, a two-part article examined the newest chemical class (strobilurins) and the oldest chemical class (coppers). When GPN came to me with their request early this fall, I asked myself a question: What could I do this year to keep both the reader and myself interested? I decided to present a short history of ornamental disease control and focus on one class of products, fungicides, and their track record on fighting ornamental diseases. I’ve done my best in this effort and hope there is something here for most readers.

A Look Back

I spend the better part of each year asking growers about their ornamental disease concerns and then performing research trials to try and address those concerns. I generally enjoy this work, thanks in no small part to the very high level of interest and participation of the product manufacturers in the ornamental industry.

When I started working on ornamental disease control about 20 years ago, ornamentals were overlooked, at best, when it came to interest from the agricultural chemical companies. The zero-tolerance for disease expression on ornamentals, the market’s complexity with the multitude of segments and cultivars and the industry’s relatively low dollar return made registrations on ornamentals less than appealing for many companies. In the early 1990s, we compounded the unattractiveness of the ornamentals market by involving ourselves in legal battles against the few companies who had registered their products for ornamental use. Ten years later, it’s a wonder how we arrived at the present abundance of products for disease control in our industry. The explanations are no doubt complex, but the benefits are there for all to see.

We now have more products in every conceivable category for disease control on ornamentals than ever before. I can illustrate this point with a short trip down memory lane to take a look at the introduction of fungicides into agriculture – not necessarily registrations on ornamentals. (Please note that I have listed several trade names along with the active ingredients simply to remind the reader of a name they may better recognize, not to make recommendations about a product.)

Copper is one of the oldest fungicide products – with its first use in about 1761. One of the most effective applications was a Bordeaux mix, a combination of copper sulfate and lime. Sometime during the 1800s, sulfur was introduced for control of powdery mildew. In the 1930s, PCNB (Terraclor) was introduced, and in the 1940s, streptomycin and captan. In the late 1950s and early ’60s, products containing mancozeb and dichloran (Botran) were introduced.

Then the real growth of the disease control industry occurred. In the 1960s, benomyl, thiophanate methyl (Fungo), triforine (no longer available) and etridiazole (Terrazole) were introduced. The 1970s could be labeled “the Botrycide decade,” with iprodione (Chipco 26019), vinclozolin (Ornalin) and chlorothalonil (Daconil) introduced, as well as fosetyl aluminum (Aliette), metalaxyl (Subdue), flutolanil (Contrast), triadimefon (Strike) and propiconazole (Banner Maxx). Many of these compounds were somewhat selective in the pathogens they affected, such as pythiaceous fungi (fosetyl aluminum and metalaxyl).

In the 1980s, we witnessed the introduction of many more sterol inhibitors, such as tebuconazole (Lynx) and triflumizole (Terraguard), as well as dimethomorph (Stature) and fenhexamid (Decree). Most recently, we have seen the additions of fludioxinil (Medallion – 1990), kresoxim methyl (Cygnus – 1990), azoxystrobin (Heritage –1992) and some biological controls including Trichoderma (RootShield – 1995) and Bacillus (Serenade – 1997).

New products and formulations will continue to be released. But we should never overlook the old standbys. In October, I attended an IR-4 workshop for ornamental disease control and one of the “newest” products touted was Bordeaux. It seems as if we’ve come full circle.

A Review of What Works

In 1999, I wrote, “Some new products have characteristics, such as mode of action, source and range of efficacy, that we have become familiar with in previous products. Others have new modes of action, have been derived from novel sources or have greatly improved efficacy, which make their introduction especially exciting. Still others are biological pesticides since they are microorganisms that are living when applied to the crop and must be kept alive during the production of that crop.” That statement remains true today, although the list of available products is much longer than it was two years ago. Today’s list also includes many more “green” products, biological agents and some truly new chemistry. (I will once again apologize to manufacturers of those products that are not included in some fashion in this article. Inclusion of a product is not meant as an endorsement and therefore omission is not meant as a slight.)

Many new products with new chemistries are being investigated by a number of chemical companies. Much of the new chemistry is originating in Japan, although development appears to be accomplished through U.S. or European companies. Partnerships between standard agricultural chemical companies and those dedicated to specialty crops such as ornamentals, turf and aquatics have been formed in the past five years with excellent results for the ornamental plant producer. Many of the large ag chemical companies appear intent on becoming larger by merging with other large companies (i.e., the recent merger of the ag divisions of Novartis and AstraZeneca to form Syngenta). This has been accompanied by a proliferation of smaller companies specializing in ornamentals.

A review of fungicides and their efficacy against certain diseases is summarized in Table 1 on pg. 33. This table represents four years of testing at Chase Research Gardens for ornamental disease control. The majority of the products included are currently labeled somewhere in the United States. Table 1 includes 29 products, which I admit is not comprehensive. Some products could not be included due to space constraints, as well as a lack of sufficient experience with them on my part. The 13 categories of diseases listed include subcategories for each disease. For example, Fusarium would encompass Fusarium leaf spot and Fusarium wilt diseases. Table 2 indicates the limits of the testing represented in Table 1.

The table results are presented using the following code system. First, a single word indicates either that a single trial was performed on that product or that the product consistently performed against that pathogen. Any range of responses indicates multiple testing over the past four years. A rating of none indicates that the product showed no control against the pathogen. In the normal course of growing, products tend to perform within a given range depending upon the disease pressure, means of applications (rates and intervals) and susceptibility of the host plant. It pays to keep in mind that even the best fungicides are not remarkably effective against very severe disease pressure such as Cylindrocladium root and petiole rot on spathiphyllum or Fusarium wilt on cyclamen. In addition, some plants are so susceptible to a disease that control is difficult (i.e., downy mildew on alyssum in the Pacific Northwest).

Note: Please use the information in the tables provided with caution. After all, these are research results and your personal experience with disease control should be your ultimate authority. And as always – follow the labels – they are the law. Sometimes you will even find them helpful.

A.R. Chase

A.R. Chase is plant pathologist at Chase Agricultural Consulting LLC and can be reached at archase@chaseresearch.net.

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