107a trade-off between acceptable levels of yield loss and effective weed seed control.
A consequence is that there frequently is little or no ‘window of opportunity’ for the
application of effective crop-topping treatments. Despite this crop-topping is rou-
tinely used in non-cereal crops (e.g. lupins, peas, chickpeas) where some yield loss
is often tolerated in preference to maximising weed seed control.
4 Harvest Weed Seed Control
The biological attribute (weakness) of seed retention at maturity in annual ryegrass,
wild radish and other annual weed species, means that at crop maturity seed heads
remain intact and at a height that enables weed seeds to be collected (harvested)
during grain crop harvest (Fig. 3 ). For example, in field crops a large proportion
(~80 %) of total annual ryegrass seed production can be collected during a typical
commercial grain harvest (Blanco-Moreno et al. 2004 ; Walsh and Powles 2014 ).
Grain harvest presents an opportunity to target weed seed production, thereby mini-
mizing replenishment/increase of the weed seed bank. HWSC systems have been
developed, principally in Australia, that target and destroy weed seeds during com-
mercial grain crop harvest preventing inputs into the seed bank (Walsh et al. 2013 )
(Fig. 2 ).
A number of HWSC systems have been developed for the specific purpose of
targeting weed seed during crop harvest, restricting contributions to the seed bank
thereby reducing subsequent in-crop interference (Walsh and Newman 2007 ; Walsh
Fig. 3 Upright and intact annual ryegrass seed heads in mature cereal crop
Weed Management in Dryland Cropping Systems