101The increasing need to improve soil structure, retain nutrients, and conserve soil
moisture will continue to drive the widespread adoption of conservation cropping
practices (FAO 2015 ; Kassam et al. 2012 ; Llewellyn et al. 2012 ). These systems are
now proven to be more robust and sustainable, providing some stability in spite of
highly variable climatic conditions. Thus, even though conservation cropping has
led to herbicide reliance and subsequently herbicide resistance, this approach has
provided substantial gains in productivity and reverting to less conservative systems
for the sake of weed control is no longer an option.
Australia boasts arguably the most effective dryland crop production systems in
the world. Despite very low and infrequent rainfall events and low natural soil fertil-
ity levels, Australian cropping systems have evolved, adapted and even flourished.
Although cropping systems are generally successful, there have at times been major
production constraints that needed addressing. Recently the most significant of
these has been evolution of herbicide resistance and the need to weed control. Faced
with the most dramatic and extensive herbicide resistance problems in the world,
the Australian weed control industry has been forced to develop strategies that miti-
gate and mange this problem. In this chapter, recent developments in weed manage-
ment in Australia are highlighted, which may serve as a warning and an opportunity
for weed managers in dryland production regions of the world.
2 Weed Control in Australian Dryland Cropping Systems
There are at present six recognised opportunities annually for targeting weeds in
dryland crop production systems (Fig. 1 ). The attributes of these opportunities as
they have been implemented in Australian dryland production systems are discussed
below in detail.
2.1 Out of Season Weed Control
Successful crop production in water limited environments is fundamentally depen-
dant on the effective supply of soil water for crop plant growth. Wherever possible
rainfall including out of season (summer) rainfall should be conserved, particularly
in dryland cropping regions where summer rainfall dominates (Fig. 1 ). Summer rain
stimulates the emergence of annual weeds (e.g. Conyza spp., Echinochloa spp.,
Chloris virgata etc.) and although these weeds do not interfere directly with crop
growth they must be controlled to prevent the use of soil moisture and nutrient
reserves for subsequent crop growth (Hunt et al. 2013 ) (Fig. 2 ). Prior to the intro-
duction of non-selective herbicides (e.g. glyphosate, paraquat/diquat) in the 1970s,
cultivation was used to control any summer rainfall stimulated weed emergence, as
well as for seedbed preparation. Summer weed control is now almost exclusively
Weed Management in Dryland Cropping Systems