Chris Buddenhagen told the folk at the 2022 LandWISE AGM Seminar in late June about research progress in the AgResearch Managing Herbicide Resistance programme,

Working with FAR, the Bragato Research Centre, and Massey University, AgResearch scientists are surveying arable farms and vineyards for presence of herbicide resistant weeds. They have collected seed from across Aotearoa including Canterbury, Otago, Marlborough, Waikato, Bay of Plenty, Gisborne, Hawke’s Bay and Wairarapa.

The first time a deliberate survey looking for examples of herbicide resistance has been conducted, the research is adding to the number of known cases in New Zealand.  As can be seen in the chart below, grasses feature prominently, some to several herbicide groups.

Chris explained that resistance results from plants with certain genes or sets of genes being preferentially selected by the management to which they are exposed. Plants constantly mutate, and a constant exposure to a certain stressor (in this case a herbicide group) means those that cope best will survive and, over time, become the dominant population. 

To identify resistance, seed has been collected from suspected survivors and from soil samples taken from the survey sites.  The seeds are germinated in a greenhouse, and sown in trays for testing.

Once established, the trays are sprayed at a defined spray rate, and plants observed for about three to six weeks. 

After a few weeks, the results of spraying become apparent. Some lines are shown to be susceptible to a particular spray, and others resistant.

Identifying resistance this way is slow and expensive. The project is also investigating other rapid testing techniques including the use of genetic markers so any plant sample can be tested virtually overnight, and at much lower cost. But that’s a story for another day.

If you want to read about the Herbicide Survey work in detail, information from the first surveys is available online as an open access publication.

See:  Buddenhagen CE, James TK, Ngow Z, Hackell DL, Rolston MP, Chynoweth RJ, Gunnarsson M, Li F, Harrington KC, Ghanizadeh H. 2021.  Resistance to post-emergent herbicides is becoming common for grass weeds on New Zealand wheat and barley farms.  Uludag A, editor. PLoS ONE. 16(10):e0258685. https://doi.org/10.1371/journal.pone.0258685

We thank Chris, Trevor James and all involved in the work for presenting it to the LandWISE Seminar participants.