July 2002

What About Generics? By A.R. Chase

The high cost of human health care, especially prescriptionmedications, has led many of us to that very question. Can I use the generic,less-expensive product or must I purchase the name brand? Although we do nothave true generics available for our plant health care needs, we are faced withessentially the same question: What about using a generic?

As with most simple questions, the answer is complex. Overthe past couple of years, Chase Research Gardens has sought an answer to thisquestion for ornamental disease control through a series of trials withside-by-side comparisons of fungicides with similar active ingredients. As onemight expect, these tests are not popular with all fungicide manufacturers, somany of these trials are my own fault with no one to share the blame. Somecompanies will be gratified by the results we found while others will not. I doapologize for leaving products out of these tests, but they were my own idea andthus subject to my whims. The chemical class, active ingredient and rates ofthe products tested are summarized in Table 1, page 32.

Coppers and Mancozebs

Perhaps the oldest fixed copper fungicide is copper sulfatepentahydrate, first used in the 1800s. Today, Phyton 27 is the best knownexample of this type of copper product. In 1889, basic copper was the firstfactory-made fungicide. Nearly 70 years later, cupric hydroxide entered themarketplace. Examples of products with this active ingredient are Champ andKocide. Most recently we have Camelot (copper salts of fatty and rosin acids).

In the fall of 2000, we collected some 1-gallon azaleas withpowdery mildew and tried to eradicate the problem with a couple of fungicidesprays. The products were copper and mancozeb (alone or in combination[Junction]). It is clear from this test (see Figure 1, top right) that allproducts worked reasonably well (to about the same degree) to reduce the leafarea affected by powdery mildew.

Dithiocarbamate products such as mancozebs have been used tocontrol many foliar diseases on ornamentals for years. The azalea powderymildew test showed similar control with Junction (cupric hydroxide andmancozeb), Dithane NT Rainshield and Protect T/O (both mancozeb). We also comparedsome mancozeb fungicides (as well as sterol inhibitors) for control ofAlternaria leaf spot on Pittosporum. These liners had severe disease when wepotted them up and started the fungicide therapy program. In this trial ProtectT/O, Dithane NT Rainshield, Zyban (mancozeb and thiophanate methyl) and RH-0611(myclobutanil and mancozeb) all gave excellent disease control (See Figure 2,above). In addition, the sterol inhibitors (triazoles) Terraguard, Systhane andBanner Maxx were also excellent.

The severe outbreak of poinsettia scab in the late summer of2000 led to the test reported here. We trialed quite a few differentfungicides, and several containing mancozeb were among those tested. Allmancozebs tested (Stature is a combination of dimethomorph and mancozeb) gaveexcellent preventative control of poinsettia scab (see Figure 3, above right).

Chlorothalonils

The final group of fungicides we were interested incomparing were those containing chlorothalonil — a long-time standard forleaf spot control on ornamentals. Our first test was on impatiens withAlternaria leaf spot. The plants were healthy when we started so this trial waspreventative in nature. Products included were two formulations each of Daconiland PathGuard. The results we obtained showed that each of the chlorothalonilfungicides provided very good to excellent prevention of Alternaria leaf spoton this bedding plant (see Figure 4, below).

Some of the same products were included in a trial lastspring on daylily leaf streak. In this case, we also included two formulationsof Concorde as well as two combination products containing thiophanate methyland chlorothalonil (ConSyst and Spectro). While disease prevention was onlymoderate, it certainly was equivalent with all of the fungicides included (seeFigure 5, below).

Which to Use?

For the few products and diseases tested under thesecontrolled settings, I would be hard-pressed to find any differences betweenfungicides with the same or similar active ingredients. I have overall foundthe fungicides within any one of these groups (copper, mancozeb, chlorothalonilor sterol inhibitor) to control many diseases to a similar degree.

Keep in mind that the diseases I have reported here arerelatively easy to control. In cases where disease pressure is exceptionallysevere or the disease itself difficult to control, even slight differences canbe critically important. For example, Phyton 27 has given slightly bettercontrol of bacterial disease than other copper products tested. Further, one cannotcontrol Fusarium wilt on Cyclamen with any sterol inhibitor — onlyTerraguard has proven effective in our trials. Finally, we have foundsignificant Á differences between the strobilurin fungicides despite thesimilarities of their active ingredients. 

So what’s the answer to the question I posed at thebeginning of this article? Sometimes you can go with the least-costlyfungicide, while other times you must use a specific fungicide. No simpleanswers in this life.

Editor’s Note: The use of specific trade names in thisarticle 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 themagazine.