Ornamental Disease Control Products —2002 Update By A.R. Chase

Last year, for the first time, GPN published a table, summarizing efficacy results for fungicide and bactericide ornamental trials at Chase Research Gardens. This year, we decided to do the same thing as an annual update.

This chart represents five 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, though you should check the label to see if they are registered for use in your area. Table 1 includes 31 products, two more than last year, but we recognize that this is still not an exhaustive list. There are 15 groups of diseases listed, with most lumped together for space conservation. I added Anthracnose and scab (poinsettia) this year. I could have added a couple of other leaf spot diseases (daylily streak and fairy ring leaf spot on dianthus), but since the results were the same as for Alternaria leaf spot, I included the information in that column.

The results are presented using the following code system : None = no control; Poor, Fair and Good are self-explanatory; Vgood = very good; and Exc = excellent. A single word indicates either that a single trial was performed or that the product consistently performed against that pathogen. Any range of responses indicates multiple testing over the past four years and/or varying results. In the normal course of growing, products tend to perform within a given range, depending on the disease pressure, means of application (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 unless the environment can be controlled (downy mildew on alyssum in the Pacific Northwest).

Rotation of Products

Rotation of products is critical for many, if not all, of the diseases we encounter during production of ornamental crops. We have heard for years about the need for rotation to manage (hopefully stop) resistance of pathogens and insects to fungicides and insecticides. Resistance to fungicides is not as common in some parts of the country as in others, but our manner of transporting rooted cuttings from all over the country means we are moving potentially resistant populations of our pests/diseases as well. Even if you have never used a particular fungicide, you might find your Botrytis is resistant to it due to use at the propagation level.

Comparisons of rotation from three chemical classes (groups) versus tank mixing generally indicate that both work. I tend toward preferring rotations for foliar diseases such as powdery mildew or Botrytis blight and tank-mixes for soil-borne diseases such as root rot.

There are other reasons that rotations are important.Something that we don’t usually consider is to make sure we have more than one source of our products for pest management in the future. The producers of our chemical and biological control products are merging to form bigger and bigger companies with control of more and more chemicals. Novartis merged with Zeneca to form Syngenta early this year. In the middle of the year, Rohm & Haas merged with Dow AgroSciences. Most recently, Aventis (formerly Rhone Poulenc and Agrevo) will merge yet again. This trend has been underway for at least the past five years.

The variety that was only recently available to us is is appearing rapidly. Competition between manufacturers helps ensure the most reasonable cost as well as appropriate formulations, container sizes and other needs specific to our industry. I suggest rotation between chemical companies when possible. I have heard a number of growers express this idea when discussing who they purchase plugs from, and I hope they extend this to other materials they consume.

A New Guide

I have been struggling, with little success, for the past two years to present information on rotating between different chemical classes. I remember what products belong to each chemical class (most of the time), but it is obviously not easy for most growers to remember. I am easily reminded of this human failing when asked about insecticides. My knowledge of them is usually lower than that of the grower asking me the question.

My husband Mike suggested a slide rule format, and I think we have finally come up with a decent delivery system for this information. The multitude of products (Table 1) can be overwhelming to decipher, so I have trimmed down the list to the best three products for control of eight different disease groupings. The slide rule has information on fungal leaf spots, Botrytis blight, bacterial diseases, Cylindrocladium and Fusarium, downy mildew, Phytophthora and Pythium, powdery mildew and rust, and Rhizoctonia. A total of 12 products were included. I chose the products based on how well they worked, chemical class (each of the 12 is in a separate chemical class) and chemical companies — I wanted to represent as many as possible. As it turns out, nine companies for the 12 products were chosen. Application method (spray of drench), interval, symptoms and cultural controls in an abbreviated form are included. The rotation guide slide rule will be produced in cooperation with GPN and will be available sometime in 2002.

Please use the information in this article with a grain of salt or maybe more. After all, ç these are research results and your personal experience with disease control should be your ultimate authority. Humans have two characteristics that can get them into trouble here. The first is to assume anything in print by a big-time doctor is right and the second is to stick with the status quo whether it is working or not.Think about what you read and hear and use it if it makes sense. And as always — FOLLOW THE LABELS — they are the law. Sometimes you will even find them helpful.

 

Author’s note: For those products not included in the Table, I reiterate that I do not write about products I have not tested personally. I apologize for being so difficult.

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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