Isoproturon-Resistant Littleseed Canarygrass (Phalaris minor) and its Response to Alternate Herbicides¹

Abstract

Littleseed canarygrass, a troublesome wheat weed, has developed resistance against isoproturon in India. Laboratory, pot, and field experiments were conducted to quantify the level of isoproturon resistance in various littleseed canarygrass biotypes and to evaluate the response of isoproturon-resistant littleseed canarygrass to alternate herbicides. For quantification of resistance, 10 littleseed canarygrass biotypes were collected from fields with a varied history of cropping and herbicide use. Pot studies indicated that 6 out of the 10 biotypes tested were resistant to isoproturon. The resistant (R) biotypes had 50% growth reduction values, 5 to 10 times greater than that of the most susceptible biotype. The R biotypes were from areas where isoproturon had been used continuously for more than 10 yr in wheat under a continuous rice–wheat cropping system. The isoproturon resistance was not detected where crops and herbicides were rotated. Under field conditions, postemergence isoproturon at 1,000 g/ha 32 d after sowing failed to control littleseed canarygrass and as a result wheat grain yield decreased by 65% compared with the weed-free control. The herbicides observed to be effective in wheat against isoproturon-resistant littleseed canarygrass were CGA 184927 (50 to 60 g ai/ha), fenoxaprop-p-ethyl (100 to 120 g/ha), ICIA 0604 (350 g ai/ha), and MON 37503 (25 g ai/ha). The use of these herbicides increased the grain yield by 200% or more when compared with the weedy check. Among the herbicides tested, MON 37503 at 25 g ai/ha was the best because of complex weed flora control and produced wheat yield similar to that of the weed-free control. Based on this study, the absence of resistance when herbicides and crops were rotated indicates that growers should follow herbicide and crop rotation in order to avoid development of herbicide resistance in the near future. The integration of this system (crop and herbicide rotation) with cultural and mechanical means of weed control could be further targeted as a long-term strategy for resistance management.

Crop Growth and Yield Losses in Wheat Due to Little Seed Canary Grass Infestation Differ with Weed Densities and Changes in Environment

“…The ability of dormant seeds to survive during rice period is a major fact for its prevalence in wheat-rice cropping system (Malik et al, 1998). Oad et al (2007) have reported that LCG infestation can reduce wheat yield by 35% and its heavy infestation might incur a complete crop failure (Chhokar and Malik, 2002).…”

Evaluation of Fenoxaprop-P-Ethyl Resistant Littleseed Canarygrass (Phalaris minor) in Pakistan

“…Heap (2015) reported that the herbicide selection pressure is continually increasing the resistant biotypes of different weeds. After the first case of P. minor resistance to isoproturon during 1995 in India, P. minor biotypes have developed resistance to ALS-inhibiting herbicide (sulfosulfuron), ACCase-inhibiting herbicides (clodinafop, fenoxaprop and tralkoxydim) and other herbicides with these modes of actions (Chhokar and Malik, 2002;Chhokar and Sharma, 2008;Gherekhloo et al, 2011). Many P. minor biotypes have evolved cross and multiple resistance to herbicides, having different modes of action in different parts of the world (Heap, 2015).…”

Effects of herbicide applications in wheat fields

“…Chhokar and Malik 36 showed that under field conditions, at post-emergence isoproturon at 1,000 g/ha 32 d after sowing failed to control littleseed canarygrass and as a result wheat grain yield decreased by 65% compared with the weed-free control. Singh 37 reported that dry weight of S biotype was significantly reduced at 0.25 kg/ha of isoproturon.…”

“…Extensive use of isoproturon over many years has led to the evolution of resistance in Phalaris minor in northwest India. 36,40 Therefore, continued reliance on isoproturon after the development of resistance resulted in a heavy build-up of Phalaris minor populations, as competition from other weeds was removed. This caused heavy yield losses in wheat.…”

“…[40][41][42] (2) The recommended dose of isoproturon (1,000 g a.i./ha) was not effective against P. minor due to resistance development and a double dose (2,000 g a.i./ha) failed to provide effective control and resulted in large scale yield reduction in wheat. 36,40 Alternative herbicides used for control of isoproturon resistant Phalaris minor were cloninafop, fenoxaprop, trialkoxydim and sulphosulfuron. Sulphosulfuron 36 at 25 g /ha was found to be best for control of Phalaris minor and many broad leaf weeds.…”