Cross‐resistance of Bidens subalternans to acetolactate synthase inhibitors in Brazil

Abstract

Summary Weeds resistant (R) to herbicides are widespread worldwide. Bidens subalternans is one of the most troublesome weeds in conventional soyabean fields in Brazil, and in a crop rotation system of cotton/soyabean and maize/soyabean some populations had evolved resistance to acetolactate synthase (ALS)‐inhibiting herbicides. Bidens subalternans plants suspected of resistance were observed in soyabean fields where the main ALS‐inhibiting herbicide sprayed is chlorimuron‐ethyl. To confirm and characterise the resistance of B. subalternans to ALS inhibitors, whole‐plant bioassays were conducted in 2006 and 2008. ALS in vivo enzyme bioassays were also conducted in 2007. In both bioassays, the R biotype showed cross‐resistance to four chemical families of ALS‐inhibiting herbicides. According to whole‐plant level tests the R biotype showed 498‐, 797‐, 726‐ and >877‐fold resistance to chlorimuron‐ethyl, imazethapyr, cloransulam‐methyl and pyrithiobac‐sodium herbicides respectively. The R biotype was also 17‐, 166‐, 436‐ and 516‐fold R to chlorimuron‐ethyl, imazethapyr, cloransulam‐methyl and pyrithiobac‐sodium herbicides, respectively, based on the enzyme assay. Therefore, the herbicide‐R B. subalternans can no longer be controlled by any ALS‐inhibitor herbicides. Integrated control methods involving alternative herbicide with different modes of action are needed, to avoid yield losses in conventional soyabean fields in Brazil that are infested by ALS‐R B. subalternans populations.

COMPETITIVE ABILITY OF WHEAT IN ASSOCIATION WITH BIOTYPES OF Raphanus raphanistrum L. RESISTANT AND SUSCEPTIBLE TO ALS-INHIBITOR HERBICIDES

“…There were no significant differences in the competitive ability between resistant and susceptible biotypes of Bidens subalternans Vidal;Burgos, 2011). Bidens pilosa biotypes susceptible to ALS inhibitors exhibited higher dry matter accumulation in the early growth stages compared to the resistant biotypes; however, at the end of the cycle, this characteristic became similar, with no differences between them (Christoffoleti, 2001) .…”

Weed Phytosociological Survey in Irrigated Rice

“…However, the continuous use of the Clearfield ® technology, in which the chemical handling employ herbicides with similar action mechanisms, may select for resistant weed populations. According to Lamego et al (2009), the reiterate use of herbicides with the same action mechanisms during a long time results in the selection of resistant specimens.…”

Globe fringerush (Fimbristylis miliacea) cross resistance to als-inhibitor herbicides under field conditions in irrigated rice in the south of Brazil

“…There was a significant interaction effect of herbicide x dose (p≤0.05) on rice yield chemical groups of ALS inhibitors: sulfonylurea, pyrimidylthiobenzoates and triazolopyrimidines; agreeing with this present study (Figure 2 and 3). The crossresistance to different families of ALS inhibitors commonly occurs, for instance in ALS-resistant Amaranthus palmeri (Burgos et al, 2001), Bidens subalternans (Lamego et al, 2009), Cyperus difformis (Merotto Jr. et al, 2009) and many others. Imidazolinone herbicides are also labeled for Clearfield ® rice in Brazil.…”

“…Sulfonylurea herbicides, such as pyrazosulfuron-ethyl, are important tools for rice weed control in Santa Catarina. However, the repeated use of pyrazosulfuron has led to resistant globe fringerush biotypes, a common Globe fringerush (Fimbristylis miliaceae) cross resistance to ... consequence of the intensive use of ALS inhibitors on other species (Burgos et al, 2001;Lamego et al, 2009;Merotto Jr. et al, 2009;Massa, et al, 2011).…”