Alicia Cirujeda, Ramon Tarrago,  Jordi Recasens, Andreu Tabener

During the cropping season 1998/99, four field experiments were conducted in winter cereal fields with a high infestation of resistant Papaver rhoeas in Catalonia (North-eastern Spain). Two fields had resistant poppies to both herbicides and two had poppies resistant to tribenuron but susceptible to 2,4-D. Seventeen combinations of pre- and early and late post-emergence herbicides were tested. The experiments were designed in three blocks containing the randomly distributed 10 m2 pots. Application was done with an AZO sprayer. Evaluations were done counting living plants in a square meter three times in each plot every fortnight after treatment, and Abbot efficacy of each evaluation was calculated. The pre-emergence herbicides tested had high efficacy in all the tested fields where they were applied: pendimethalin (1.65 L a.i. ha-1, trifluralin + linuron (0.72 L a.i. ha-1 + 0.36La.i. ha-1) and trifluralin + chlortoluron (0.72 L a.i. ha-1.+-l.25 L a.i. ha-1)... No phytotoxicity on the cereals was detected in any case. In early post-emergence, the most effective group was the HBNs. The mixtures containing bromoxynil gave a high control in all fields, followed by the mixtures containing ioxinil. Diflufenican in mixture with MCPA (0.0375 + 0.375 L a.i. ha-1) gave good results in three locations. Isoproturon + diflufenican (1.35 + 0.126 L a.i. ha-1) controlled P. rhoeas at two locations only. Good control was achieved with tribenuron + metribuzin (0.015 + 0.07 g a.i. ha-1) and with triclopyr + chlortoluron (0.48 + 1.25 L a.i. ha-1) at also two locations. Terbutryn + triasulfuron (0.297 + 0.03 L a.i. ha-1) had high efficacy in only one location. In late post-emergence, 2,4-D (0.6 L a.i. ha-1) gave good control only at the two susceptible fields to this herbicide. The mixture 2,4-D with florasulam (0.3 + 0.00625 L a.i. ha-1) was effective at the same two sites only. Dicamba at 0.192 L a.i. ha-1 gave high control at two locations only. A short-term control of the herbicide resistance of P. rhoeas to tribenuron and to 2,4-D seems possible with chemical methods, especially by using HBN's or pre-emergence herbicides.

KATI V, SCARABEL L, THIERY-LANFRANCHI D, KIOLEOGLOU V, LIBEROPOULOU S, & DELYE C (2019). Multiple resistance ofPapaver rhoeas L. to 2,4-D and acetolactate synthase inhibitors in four European countries. Weed Research 59, 367–376.

Summary

The issue of cross- or multiple resistance to acetolactate synthase (ALS) inhibitors and the auxinic herbicide 2,4-D was investigated in Papaver rhoeas L., a common and troublesome weed in winter cereals, in a broad-scale study across four European countries. A combination of herbicide sensitivity bioassays and molecular assays targeting mutations involved in resistance was conducted on 27 populations of P. rhoeas originating from Greece (9), Italy (5), France (10) and Spain (3). Plants resistant to the field rate of 2,4-D were observed in 25 of the 27 populations assayed, in frequencies ranging from 5% to 85%. Plants resistant to ALS-inhibiting herbicides (sulfonylureas) were present in 24 of the 27 populations, in frequencies ranging from 4% to 100%. Plants resistant to 2,4-D co-occurred with plants resistant to sulfonylureas in 23 populations. In four of these, the probability of presence of plants with cross- or multiple resistance to 2,4D and sulfonylureas was higher than 0.5. ALS genotyping of plants from the field populations or of their progenies, identified ALS alleles carrying a mutation at codon Pro197 or Trp574 in 2,4-D-sensitive and in 2,4-D-resistant plants. The latter case confirmed multiple resistance to 2,4-D and ALS inhibitors at the level of individual plants in all four countries investigated. This study is the first to identify individual plants with multiple resistance in P. rhoeas, an attribute rarely assessed in other weed species, but one with significant implications in designing chemical control strategies.