Fenpyrazone effects on succeeding crops in annual double-cropping areas on the North China Plain

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Fenpyrazone is a novel 4-hydroxyphenylpyruvate dioxygenase (HPPD)-inhibiting herbicide used for postemergence (POST) application to control annual monocotyledon and dicotyledon weeds in summer maize (Zea mays L.). Annual double-cropping systems are popular on the North China Plain, especially summer maize in rotation with winter wheat (Triticum aestivum L.) or garlic (Allium sativum L.). In addition, vegetable crops have shown different levels of sensitivity to HPPD-inhibiting herbicides that were applied to preceding maize fields. However, there is no information about the effects of fenpyrazone on the succeeding crops. Here, field experiments were conducted twice at Dawenkou and Mazhuang to evaluate the response of successive rotation crops such as winter wheat, garlic and spinach (Spinacia oleracea L.) to fenpyrazone that was applied to preceding summer maize fields. Compared with the untreated weed-free control, none of the fenpyrazone treatments resulted in significant differences in the emergence of wheat, garlic and spinach at either location. When fenpyrazone was applied at 3 times the recommended rate to the preceding maize fields, there was no significant reduction in the wheat and garlic biomass despite the height of the garlic plants being reduced by 4.1% at 20 d after sowing (DAS) compared to that of the untreated weed-free control. Compared with wheat and garlic, spinach was more sensitive to fenpyrazone applications to preceding summer maize fields, and it reduced the plant heights by 2.6–17.1% at 20 DAS compared to those in the untreated weed-free control, with the loam soil in Mazhuang causing a higher biomass reduction than the sandy loam soil in Dawenkou. However, the biomass reduction stopped at 40 DAS, and no yield reduction was observed at harvest for all the fenpyrazone treatments at both locations. Based on this study, farmers on the North China Plain can safely grow winter wheat, garlic and spinach following fenpyrazone POST application at the recommended rate to preceding summer maize.