AgNet, 8 March 2004

Performance of generic phosphite fungicides: A status report

Kentucky Pest News No. 1011; University of Kentucky; http://www.uky.edu/Agriculture/kpn/kpn_04/pn040223.htm#lawper 

During the past decade, Chipco Signature fungicide (active ingredient fosetyl-Al) became a "keystone" product for disease control programs on many golf courses across the country. This is in part because of the general enhancement in quality on stressed turfgrass that has been reported in some studies, including selected tests at the University of Kentucky. The product is also known to provide control of Pythium cottony blight in many circumstances, particularly when sequential applications are made.

Fosetyl-Al is absorbed into the plant and converted to a phosphite (=phosphonate) ion (PO3-). An interesting and important fact is that the phosphite ion is the principal chemical responsible for disease control. Although a variety of chemically simple, inexpensive phosphite salts were known to provide disease control in the late 1970's, the language of Rhone-Poulenc's patent apparently permitted exclusive development of phosphite materials as fungicides. After fosetyl-Al recently came off patent, several fungicide manufacturers and formulators brought to market phosphite materials as fungicides. Turf fungicides for which I have current labels include Magellan, Resyst, Alude, Prodigy Signature, and Vital. The active ingredients in all these turf fungicides are phosphite salts, such as potassium phosphite, ammonium phosphite, sodium phosphite, and aluminum phosphite. These salts release phosphite ions onto the leaf surface, which are taken up by the plant. Thus, in theory, these phosphite fungicides should provide equal performance to fosetyl-Al. In reality, determining how generics compare to a well-established fungicide like fosetyl-Al will take several years of study. However, a status report of the research to date will undoubtedly be of interest to the many users of generic phosphite fungicides. 

Summary of Available Data

Last summer, in our first year of systematic comparison of phosphite fungicides at UK, I was surprised to see significant differences in performance among the materials (see Table 1). We saw variability in both dollar spot control and in overall quality in turf. (Note that we deliberately overlooked dollar spot damage in the turf quality ratings presented in Table 1, to address he question, "How would these plots look if dollar spot were controlled?")
Significant differences in formulation would likely account for the differences in performance we saw in this test.
I also reviewed all volumes of the journal Fungicide and Nematicide Tests as well as other published sources from other sources. Only a handful of tests were found, which was surprising given the number and availability of generic phosphite fungicides on the market. Results are as follows:

* For control of Pythium cottony blight, Magellan provided control that was equal to or better than Chipco Signature in both trials where it was tested.. In the only trial where tested, Alude and Vital provided control that was equal to that of Banol fungicide, a generally effective Pythium material.

* Against anthracnose, the product Fosphite did not provide any control of anthracnose.
In addition to the phosphite-based fungicides, there are several phosphite-based turf fertilizers, "nutritional supplements", and "conditioners" on the market. Most of these have not been formally tested for disease control capabilities. The only one that has, to my knowledge, is PK-Plus, which provided significant levels of anthracnose control when used in combination with Gary's Green + Ultraplex. Fertilizer materials and supplements can sometimes provide an increment of disease control, so such a result is not unheard of, but it is gratifying when this is shown in scientifically valid research trials. Unfortunately, the phosphite fertilizers do not come with explicit instructions on using them for disease control, because they cannot be marketed as disease-control chemicals without being subject to federal regulation.

Conclusion

It is my understanding that the generic phosphite fungicides are considerably less expensive than Chipco Signature. However, none has been subjected to as thorough testing as have formulations of fosetyl-Al. More testing is needed of the efficacy of generic phosphite fungicides for my comfort zone. Clearly, they all provide some disease control, but the data to date suggest they are not all equal. Whether the differences we observed in 2003 will hold up year after year remains to be seen. Whether the differences we observed in 2003 are worth the additional cost is a judgement call only the superintendent can make.