Effectiveness of alternative herbicides on three Conyza species from Europe with and without glyphosate resistance

Abstract

Glyphosate has been applied in European countries for over a decade between rows in olive groves and grape vineyards to control Conyza species [hairy fleabane (C. bonariensis), horseweed (C. canadensis) and Sumatran fleabane (C. sumatrensis)], however poor control has been observed in recent years. Glyphosate susceptible (GS) or resistant (GR) populations were assayed in each species. In addition, Conyza spp. control with alternative herbicides (alone or in mixture with glyphosate) over two years was also assessed. The GS populations of the three species were controlled with glyphosate field doses (1080 g ae ha −1). The GR hairy fleabane, horseweed and Sumatran fleabane populations were 15.0, 15.7 and 19.8 times more resistant, respectively, than their respective GS population. The shikimic accumulation of GS populations was 4-6 times higher compared with the GR Conyza populations, confirming the glyphosate resistance of the latter ones. The increase in the glyphosate dose did not control the GR Conyza populations, despite providing a higher dry growth reduction. Glufosinate and flazasulfuron, alone or mixed with glyphosate, were the effective options to control GR and GS populations of hairy fleabane and Sumatran fleabane. However, the GR horseweed population might have evolved multiple resistance to glyphosate and flazasulfuron in Hungary. The other herbicides (PSI, auxinic and PPO) showed an additive effect together with the control provided by glyphosate in the GS and GR populations; however generally, these herbicides could be applied alone at the rosette stage. Effective herbicides with modes of action different from glyphosate, except flazasulfuron for controlling horseweed, should be used to delay the selection of herbicide resistance in perennial crops in Europe. around the world (Heap, 2018). Glyphosate [N-(phosphonomethyl)-glycine] is the world's most successful post-emergence and non-selective herbicide (Duke, 2018). In Spain it has been widely used to control weeds in citrus orchards, olive groves, grape vineyards, and others perennial and annual crops (González-Torralva et al., 2010, 2014), as well as in path borders, railway lines, recreation areas and derelict sites (Urbano et al., 2007). This herbicide is absorbed through leaves and other young-green tissues, and translocated via phloem into meristematic tissues (Preston and Wakelin, 2008). Glyphosate is a potent inhibitor of 5-enolpyruvylshikimate 3-phosphate synthase (EPSPS) by blocking the biosynthesis of phenylalanine, tryptophan, tyrosine and others aromatic compounds in susceptible plants (Maeda and Dudareva, 2012).

First Case of Conyza canadensis from Hungary with Multiple Resistance to Glyphosate and Flazasulfuron

“…The variable accumulation of shikimic acid between the C. canadensis populations was in agreement with that observed in the dose-response assays, and other glyphosate resistant Conyza spp. populations from Hungary [29], confirming the resistance to glyphosate of the H-1 to H-5 populations.…”

Can Control of Glyphosate Susceptible and Resistant Conyza sumatrensis Populations Be Dependent on the Herbicide Formulation or Adjuvants?

“…Glyphosate is a broad-spectrum, foliar, non-selective and systemic herbicide acting as an inhibitor of 5-enolpyruvylshikimate-3-phosphate synthase (EPSPS) [1][2][3]. EPSPS is an enzyme that plays an important role in the shikimate pathway for the biosynthesis of aromatic amino acids: phenylalanine (Phe), tyrosine (Tyr) and tryptophan (Trp) [4,5]. Following foliar application, this herbicide is absorbed and translocated via the phloem to the apical meristematic tissues [4,6].…”

“…The evolution of resistance to glyphosate is the outcome of different mechanisms that do not allow the herbicide to block the shikimate pathway [15,16]. Overall, glyphosate resistance occurs from minor and major GR mechanisms that can be divided into two principal groups: non-target-site resistance (NTSR) and target-site resistance (TSR) mechanisms [5,[17][18][19]. NTSR mechanisms include reduced uptake of the herbicide, diminished translocation to plant tissues, biochemical degradation and metabolism of the herbicide active compound, as well as altered sequestration of glyphosate to vacuoles [12,18].…”

First Report of Glyphosate-Resistant Biotype of Eleusine Indica (L.) Gaertn. in Europe

“…In Europe, the cultivation of GM glyphosate-tolerant crops is not allowed, therefore the situation is completely different. Most European GR weed biotypes have evolved in perennial crops, such as orchards, olive groves and vineyards, and belong to the genus Conyza [6][7][8] and Lolium [9,10]. More recently, GR biotypes of Sorghum halepense (L.) Pers.…”