Tactic 2.3 Weed control in wide-row cropping
Wide rows – crop rows which are 50 cm and wider Inter-row – the strip of soil between the crop rows Crop-row – the strip of soil taken up by the crop
Shielded spraying – the practice in which shields are used to protect the crop-rows while weeds in the inter-row area are sprayed with a non-selective herbicide (see Tactic 2.3a)
Band spraying – the practice in which a given area (band) of selective herbicide is applied to weeds in either the crop-row or inter-row (see Tactic 2.3a) only
Inter-row cultivation – the practice in which weeds in the inter-row space are controlled using tillage equipment (see Tactic 2.3b).
In response to escalating herbicide resistance and to maintain cropping programs, growers and researchers are developing shielded spraying tactics for wide-row winter crops. This tactic uses non-selective (knockdown) herbicides to control weeds in the inter-row space of the crop. In some circumstances inter-row cultivation may be applicable.
Inter-row cultivation, band spraying and, to a lesser extent, shielded spraying are not new techniques. The innovation is to use them in winter growing broadacre crops.
Key benefit #1
I n c r e a s i n g r o w s p a c i n g a l l o w s i m p r o v e d w e e d control wh ile m ain tainin g or im proving crop yield.
Weed management benefits, particularly for herbicide resistant weeds, outweigh the minor risk of crop yield loss when using wide-row cropping. Research to evaluate the impact of increasing row spacing in pulses and other winter crops in the absence of weeds has been conducted across Australia. Reduction in yield was found to be negligible. Despite these widespread research results, wide-row cropping has not yet been widely adopted in the farming community, particularly in the low to medium rainfall areas (Gill and Holmes 1997).
As shown in Table T2.3-1, the yield of two chickpea cultivars in central western New South Wales was not affected when row space was increased from 1 7 cm to 65 cm (Fettell 1998). In this experiment the effect of sowing rate on row spacing and yield was also
investigated. Fettell found that there was no difference in yield with different sowing rates (recommended sowing rate and 30% above and below recommended), and also no interaction between sowing rate and row spacing on yield. Sowing rate could therefore be ruled out as a factor affecting yield.
Table T2.3-1 Impact of row spacing on the yield of two chickpea varieties at Condobolin, New South Wales (Fettell 1998)
Pulse crops have been the initial driver and subsequent emphasis for much of the wide-row research aimed at herbicide resistance management across Australia. The
Row spacing (cm) A me t h ys t yield (t/ha)
Kaniva yield (t/ha)
wide-row planting configuration has a distinct advantage, particularly when using non-selective herbicides for inter-row weed control. Use of the tactic in only one part of the crop rotation avoids excessive use of the knockdown herbicide, thus reducing the risk of herbicide resistance development.
Research has indicated that weeds (eg annual ryegrass) in the crop-row space can be problematic even when the inter-row weeds have been controlled. Depending on the weeds present and their herbicide resistance status, selective herbicides can be band sprayed over the rows, targeting the crop-row weeds.
17.5 1.2 0.9
26.3 1.4 1.2
35 1.2 1.0
50 1.4 1.2
65 1.1 0.9
Widderick (2002) investigated the effect of plant population and row spacing on the dry matter production of sowthistle and found that at a narrow row spacing of 25 cm there was minimal dry matter production of sowthistle. As row spacing was doubled to 50 cm the dry matter production of sowthistle increased. As the density of wheat was increased in the wide rows the dry matter production of sowthistle decreased (Figure T2.3-1).
40 50 cm
The impact of row spacing was studied, in the absence of weeds, over a 3-year period in wheat, canola, faba bean and chickpea at Tamworth, New South Wales (Felton et al 2004). In that environment, increasing the row spacing from 32 cm to 64 cm had very little effect on crop yield.
Key benefit #2
Cropping in wide rows enables the use of shielded in t er -r ow h er bic ide applic atio n , c ro p -ro w ban d
s p r a y i n g a n d i n t e r - r o w c u l t i v a t i o n f o r i n - c r o p
50 75 100 150
Wheat population /m 2