Herbicide resistant weeds were first reported in US corn (Zea mays L.), soybean (Glycine max (L.) Merr.), and cotton (Gossypium hirsutum L.) fields in the early 1970's. The initial reports in corn were for photosystem II inhibitors (PS II Inhibitors), in soybeans Microtubule Inhibitors and PS II inhibitors, and in cotton with Microtubule inhibitors and Nucleic acid inhibitors. Before EPSP synthase inhibitor (glyphosate) resistant weeds evolved in these crops, there was also resistance to ALS inhibitors, ACCase inhibitors, PS I electron diverters, Synthetic Auxins, and PPO Inhibitors. As glyphosate tolerant crops were introduced, much more glyphosate was used, significantly increasing the selection pressure and causing evolution of resistance to this broad spectrum herbicide in an ever increasing number of populations. The early success of glyphosate tolerant crops brought about a decreased emphasis in companies' herbicide discovery programs. Today, because of their proficient seed production, the mobility of their pollen, as well as transfer on farming equipment, glyphosate resistant Amaranthus species have spread across a large proportion of US cropping areas. Over the years, the acreages of several weed species that are resistant to various herbicide classes have increased and more recently, Amaranthus species with resistance to HPPD Inhibitor herbicides were identified. The last new herbicide mode of action (HPPD Inhibitors) in corn, soybeans, or cotton in the US was introduced over 15 years ago. With the increase in acreage of herbicide resistant weeds and the lack of new modes of action, it has become more critical than ever to steward the currently available active ingredients. Current programs and educational efforts by herbicide companies, the Herbicide Resistance Action Group, EPA, the United Soybean Board, and others will be presented.

Herbicide resistant weed communication and education programs for corn, soybean, and cotton in the US

248th National Meeting (2014)

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