Fungicide-herbicide interaction in soybean (Glycine max)

Fungicide seed treatments are becoming increasingly popular for use with glyphosate-tolerant soybean (Glycine max (L.) Merr.). This research was initiated in response to preliminary data indicating possible negative interaction(s) between certain agrochemicals. A 2-year field study was conducted to determine whether certain combinations of fungicide seed treatments and post-emergence herbicides affect soybean yield. The experiment involved six seed treatments (thiabendazole (TBZ), pentachloronitrobenzene (PCNB), captan, TBZ+PCNB+captan, fludioxonil and a fungicide-free control) and six weed control treatments (imazethapyr, imazamox, glyphosate, glyphosate+imazethapyr, glyphosate+cloransulam-methyl and a hand-weeded control). All 36 combinations were evaluated in four different environments in Illinois, USA. All fields had minimal disease pressure and were kept free of weeds (mechanically), allowing for the evaluation of chemical interactions independent of the confounding factors of herbicide and fungicide efficacy. The fungicide treatments did not significantly affect the crop's response to the herbicide treatments, as measured by visual injury ratings. In addition, neither fungicide, herbicide, nor fungicide-herbicide combination significantly affected crop yield. No significant chemical interactions were found to exist between any of the examined fungicidal seed treatments and post-emergence herbicides.