Response of Eleusine indica and Paspalum distichum to glyphosate following repeated use in citrus groves

Abstract

a b s t r a c tEleusine indica L. Gaertn. and Paspalum distichum L. are annual and perennial grasses, respectively that are widely distributed in turf and perennial cropping systems throughout Spain. Often, glyphosate is used between rows of perennial crops for control of these grasses, but variable responses have been observed. Sensitivity to glyphosate in each species was examined under greenhouse, laboratory and field conditions. In vitro tests on whole plants of both P. distichum and E. indica revealed no differences in sensitivity to glyphosate for areas with long-term use (treated; T) and no history of use (not treated; NT). The NT population of P. distichum (ED 50 73.1 g ae ha À1 ) was 11.6% more sensitive to glyphosate than NT E. indica (ED 50 81.6 g ae ha À1 ). No differences between T and NT populations of both species were observed for foliar retention of glyphosate as well as accumulation of shikimate. However, glyphosate retention and shikimate accumulation were up to 64 and 24.4% greater, respectively in P. distichum compared to E. indica. Within 96 h after treatment (HAT), foliar absorption of 14 C-glyphosate was similar among T and NT populations, but 8.8% higher for P. distichum compared to E. indica. Retention of 14 Cglyphosate in treated leaves of P. distichum was approximately 55% lower compared to E. indica. Translocation from the treated leaf into other shoot tissue (2.8-fold) and roots (8.5-fold) was higher for P. distichum versus E. indica. This would suggest that differences in E. indica versus P. distichum response to glyphosate are based upon differential retention in treated leaves and reduced movement out of treated tissue in other shoot and root tissue. In separate field experiments in citrus orchards, glyphosate and other herbicides were applied to assess control of E. indica and P. distichum over two years. Flazasulfuron and cycloxidim resulted in 90% or greater control of both species by 60 days after treatment (DAT). Only glufosinate, oxyfluorfen, paraquat and iodosulfuron resulted in >85% control of E. indica. These corresponding treatments ranged in effectiveness from 73 to 92% on P. distichum. Integration of effective herbicides with modes of action different than glyphosate should be used for management of E. indica and P. distichum and may delay the selection for resistance to glyphosate.

<b>Glyphosate efficacy on sourgrass biotypes with suspected resistance collected in GR-crop fields

“…Eleusine indica and Paspalum distichum populations from olive groves in Spain with suspected resistance and a fiveyear application history exhibited control levels greater than 68 and 78%, respectively, with 720 g ae ha -1 glyphosate at 60 DAA. At 1,440 g ae ha -1 , E. indica and P. distichum exhibited 78 and 83% weed control, respectively (Alcántara, Fernandez, Smeda, Alves, & Prado, 2016). This suggests that these glyphosate doses (the same ones used in our evaluations of sourgrass) are sufficient for weed control when resistance has not developed.…”

Mechanisms of glyphosate resistance and response to alternative herbicide‐based management in populations of the three Conyza species introduced in southern Spain

“…Such situations could lead to possible resistance in a few years. Populations characterized as resistant could be due to these events, numerous applications over successive years, increases in the recommended field dose and to not changing to another herbicide mode of action …”

“…Populations characterized as resistant could be due to these events, numerous applications over successive years, increases in the recommended field dose and to not changing to another herbicide mode of action. 28 According to the Weed Science Society of America (WSSA) and Herbicide Resistance Action Committee (HRAC), resistance is defined as taking place when the LD 50 values for a weed population are higher than the recommended field dose and are backed by the resistance mechanisms involved. Resistance factors (RFs) can vary for different reasons such as species identity, the greater or lesser susceptibility of S populations used for comparison, the resistance mechanisms involved, and the existence of multiple or cross-resistance.…”

Evidence, Mechanism and Alternative Chemical Seedbank-Level Control of Glyphosate Resistance of a Rigid Ryegrass (Lolium rigidum) Biotype from Southern Spain

“…Widespread and large populations of this weed are also characteristic of other crop types in the Mediterranean region, including fruit tree orchards, olive groves, and vineyards. Apart from being extensively cultivated in southern Australia, this plant species is also managed as a cover crop for reducing soil losses in erosion-prone crops, particularly olive groves in southern Spain (Alcántara-de la Cruz et al, 2016b). Rigid ryegrass is ranked among the weeds exhibiting most reported cases of herbicide resistance (Heap, 2017) and, currently, resistant populations appear to be highly frequent in surveyed countries, including Australia (Owen et al, 2007) and Spain (Loureiro et al, 2010), among others (Kaundun et al, 2011; Bostamam et al, 2012).…”