Alternatives to Benomyl for Management of Cercospora Leaf Spot on Turnip Greens

Abstract

Benomyl was compared with copper hydroxide, azoxystrobin, tebuconazole, acibenzolar-S-methyl, and basic copper sulfate for efficacy of cercospora leaf spot [incited by Cercospora brassicicola P. Henn] management on turnip greens [Brassica rapa L. var. (DC.) Metzg. utilis]. Treatments included various application times and were evaluated in three field experiments over 2 years. The few yield effects that occurred were not consistent between years. Copper hydroxide and basic copper sulfate were not useful alternatives to benomyl due to a combination of phytotoxicity symptoms and ineffective disease control. Inconsistent results were observed with acibenzolar-S-methyl. A single, early application of tebuconazole greatly reduced cercospora leaf spot severity relative to the control in both years. Tebuconazole may be a good alternative to benomyl if a label can be obtained. Multiple (at least two) applications of azoxystrobin may be needed to achieve the same degree of cercospora leaf spot control as would result from a single properly timed application of benomyl. Although azoxystrobin is now labeled for turnip greens, grower costs will likely increase as a result of benomyl being discontinued. Chemical names used: methyl-1-[(butylamino)carbonyl]-H-benzimidazol-2-ylcarbamate (benomyl); methyl (E)-2-{2-[6-(2-cyanophenoxy)pyrimidin-4-yloxy]phenyl}-3-methoxyacrylate (azoxystrobin); alpha-[2-(4-chlorophenyl)ethyl]-alpha-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol (tebuconazole); 1,2,3-benzothiadiazole-7-thiocarboxylic acid-S-methyl-ester (acibenzolar-S-methyl).