Crop Protection 78 (2015) 1-4

http://dx.doi.org/10.1016/j.cropro.2015.08.008

Glyphosate-resistant Lolium multiflorum and Lolium perenne populations from New Zealand are also resistant to glufosinate and amitrole

Hossein Ghanizadeh ^a, Kerry C. Harrington ^a, *, Trevor K. James ^b
a Institute of Agriculture and Environment, Massey University, PB 11-222, Palmerston North 4442, New Zealand
^b AgResearch, Ruakura Research Centre, PB 3123, Hamilton 3240, New Zealand

This study examined if glyphosate-resistant populations of Lolium multiflorum and Lolium perenne from some New Zealand vineyards were still susceptible to glufosinate and amitrole. The response of plants of one glyphosate-resistant population of L. multiflorum, population A, and two glyphosate-resistant L. perenne populations, populations J and O, to glufosinate and amitrole were evaluated and compared to susceptible populations in two dose response experiments. Based on the herbicide rates giving 50% reduction in growth (GR50 values), populations A, J and O were 3.9, 4.5 and 3.8 times more resistant to glufosinate respectively, compared to the susceptible populations in a glufosinate doseeresponse experiment. Populations A, J and O were also found to be 2.9, 5.0 and 13.1 times more resistant to amitrole respectively, in an amitrole dose response experiment. Very similar results were obtained when both dose response experiments were repeated. This is the first confirmed report of weed species that have developed multiple-resistance to glyphosate, glufosinate and amitrole. These are the three main herbicides currently used for weed control in New Zealand vineyards.

A glyphosate-resistant perennial ryegrass population is also resistant to amitrole.

H. Ghanizadeh¹, K.C. Harrington¹, T.K. James² and D.J. Woolley^1
1Institute of Agriculture and Environment, Massey University, PB 11-222, Palmerston North 4442, New Zealand ²AgResearch, Ruakura Research Centre, PB 3123, Hamilton 3240, New Zealand
Corresponding author: K.Harrington@massey.ac.nz

A dose-response experiment was conducted on a previously confirmed glyphosate resistant perennial ryegrass (Lolium perenne) population from a Marlborough vineyard to examine if it is also resistant to amitrole after an initial experiment suggested amitrole is less effective on this population. The plants of two populations of perennial ryegrass, Population O (glyphosate resistant) and Population SP (glyphosate susceptible) were multiplied up by splitting out tillers and planting them into pots. The plants were sprayed with rates of amitrole from 0 to 9600 g ai/ha and each treatment consisted of five replicates (one plant per replicate). The dry weight of plant material was measured 8 weeks after herbicide application. The data were fitted to a three parameter logistic model and the herbicide rate giving 50% reduction in growth (GR50) was calculated. The GR50 value of Population SP for amitrole was 523 g ai/ha whereas the GR50 for Population O was found to be 13.1 times greater. This is the first confirmed case of amitrole resistance evolving within New Zealand and further work is currently underway to study this resistance.