Fungicide Review: Polyoxin D

Polyoxin-D: Mother Nature’s gift for fighting Rhizoctonias (and some other important diseases).

Polyoxin-D zinc salt is the active ingredient in two turfgrass fungicides: Endorse (Arysta) and Affirm (Cleary Chemical). There’s been some switching around of names and products since 2009 (as discussed last year) when Arysta LifeScience took back the distribution rights for the 2.5% WP formulation and Cleary’s introduced Affirm, a 11.3% WDG formulation, that contained the same active ingredient. Either way, both formulations have the same range of disease control and I haven’t seen any data so far to suggest that the two formulations have any significant differences in disease control between them. Polyoxin D is classified as a FRAC Group 19 fungicide (polyoxin antibiotics) and presently, only polyoxin D is registered as a turf fungicide in the U.S. (Image to the right taken from alanwood.net)

There are a number of other polyoxins out there (polyoxin A, polyoxin B,…polyoxin J, etc.), and they all share a common “ancestry” as far as being discovered as metabolites of Streptomyces bacteria (which are commonly called Actinomycetes). Streptomyces are typically soil inhabiting bacteria and are potent producers of some very important anti-bacterial and anti-fungal antibiotics. Interestingly, antibiotics derived from Streptomyces species account for two-thirds of our commercially available antibiotics including streptomycin, chloramphenicol, tetracycline and vancomycin (anti-bacterials) and nystatin and amphotericin B (anti-fungals).

Polyoxin D was discovered in 1965 as a fermentation product of Streptomyces cacoi var. asoensis (Suzuki et al 1965 Journal of Antibiotics Ser. A), so interestingly, this molecule has been around for a long time! Commercial fungicides containing polyoxin D utilize this active ingredient in the form of a zinc salt. Why, may you ask? Because the polyoxin D molecule is extremely water soluble and it would wash off of plant surfaces easily; the zinc salt form of polyoxin D is much more stable and enhances the longevity of the fungicide on the plant surface.

Biochemically, polyoxin D inhibits the formation of chitin, which is the main component of the cell walls of true fungi (Ascomycetes, Basidiomycetes, etc.). You can see from the photo here (taken from Endo et al. Journal of Bacteriology 1970), that fungal cells treated with polyoxin D (top photo) are unable to make functional cell walls and thus can’t function normally like the untreated ones (bottom photo).

Since Oomycetes like Pythium don’t use chitin in their cell walls, polyoxin D won’t affect these “water mold” type fungi. Polyoxin D is considered a local penetrant fungicide, and does not translocate easily upwards in plants like some other systemic fungicides, so coverage is important when applying these.

The earliest use of polyoxin D was for the control of rice sheath blight (Rhizoctonia solani) in Japan back in the 1970s. Not surprisingly, for turf diseases, Endorse and Affirm would be considered strongest against Rhizoctonia diseases like brown patch, large patch and yellow patch and the Rhizoctonia-like Waitea diseases like brown ring patch and leaf and sheath spot.

In a large patch trial we did in 2008, you can see that Endorse was very good in controlling large patch.

Applications made 16 Apr and 6 May to bermudagrass

In a brown ring patch trial also conducted in 2008, Endorse provided some of the quickest control of the disease, but didn’t have as much residual as some other treatments. We suggest tank mixing Endorse or Affirm with another fungicide like a DMI (Banner MAXX, Tourney, Triton or Torque) to get good knock down and added residual.

One curative application made on 26 Apr

In our California trials, we’ve seen it been pretty good against anthracnose and although other materials seemed to be better, Endorse and Affirm could certainly be added into the summer rotation.

Six applications total from Jun to Aug, 2005 data

Other diseases on the labels include pink and gray snow molds (it seems like they are best tank mixed with another fungicide for the best control, but ask Jim about that one), red thread, leaf spots, gray leaf spot, and fairy ring.

Endorse looked pretty good vs. fairy ring in trials conducted by myself and Mike Fidanza :www.gcsaa.org/gcm/2007/may/pdfs/treatingFR.pdf

However, I can’t say that I’d recommend polyoxin D by itself for gray leaf spot, I just haven’t seen enough data to say it’s a good choice for this disease when other fungicides are available.

OK – that’s enough geeking out for tonight – until next week, signing off from the Right Coast….