Herbicide resistance in Australia: Biological and economic lessons David Pannell

Herbicide resistance  Started 1980s  Most serious HR in the world for 20 years

Annual ryegrass  The most important weed of crops  ~100% of field samples are resistant  Resistant to multiple herbicides  Mainly not related to GM crops

Farmers forced to innovate  Tactical grazing  Land-use sequencing  Crop seeding rates  Delay seeding  Shallow cultivation  Late spraying within crop  Cut crop for hay or silage  Burning  Roundup-ready canola  Harvest weed-seed control

Windrow burning

Chaff carts

Harrington Seed Destructor

Biology of HR  To avoid HR forever, must drive resistance genes to extinction within field (Neve et al., 2003) o Follow-up control  Only possible if genes rare and follow-up control very effective  Most strategies only delay resistance

Economics of HR 1  Without gene extinction, costly pre-emptive action to delay HR not economically attractive (Pannell and Zilberman, 2001; Powles et al., 2001) o Due to weed biology, not discounting  With extinction, pre-emptive action can pay, in certain cases (Weersink et al., 2005) o Esp. if big increase in weed control cost after HR

Economics of HR 2  Following HR, economics strongly favour management changes (Schmidt and Pannell 1996; Monjardino et al., 2004; Doole and Pannell 2008; Doole et al. 2009)  Farmers with serious HR rely heavily on non- chemical control o 70% practice windrow burning o Harrington Seed Destructor profitable where there is glyphosate resistance  Zero till remains better than traditional tillage

Zero tillage

Economics of HR 3  Under-controlled weed populations explode  Weed density in optimally managed fields is almost no different with vs without HR (Pannell and Zilberman, 2001)  If the only good weed control options are expensive, it is still worth doing them  Field surveys: farmers understand this (Llewellyn et al. 2009)

Economics of HR 4  Sufficient adaptation/innovation  can continue farming profitably (Monjardino et al., 2004; Doole and Pannell 2008) o Even with no subsidies

Economics of HR 5  Historically, market failure due to spread of HR was minimal (Pannell and Zilberman 2001) o farmers developed HR at ~the same rate  Glyphosate will be different o Slower and more diverse rate of development  Market failure due to information failure o Evaluation of alternative farming systems can be extremely complex (Pannell et al. 2003)

RIM  Ryegrass Integrated Management (RIM) model (Pannell et al. 2003) o 40 weed control options o 7 crop & pasture options o 10 years o Detailed biology (weed population dynamics, inter- and intra-species competition, germination timing, seed dormancy and natural mortality, …) o Economics (NPV of strategies for farmers)  Thousands sold, now free online

The future  No silver bullet o Weeds will evolve resistance to any control method o Need diversity  2000 survey: farmers optimistic about new modes of action (Llewellyn et al. 2002, 2007) o No current basis for this o Would not last long anyway  Glyphosate resistance

Glyphosate resistance  Very little glyphosate resistance so far  But it’s coming (slowly)  Only one Roundup Ready crop (canola)  Farmers are doing things to slow it down  Australian farmers will try to stick with zero tillage even without glyphosate

To obtain RIM: ahri.uwa.edu.au/research/rim