Tactic 3 Weed control in wide-row cropping Glossary
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Benefits Key benefit #1 S h ield ed s pr a yin g al lo w s in t er - r o w app lic at io n o f non-selective herbicides in-crop, which can increase crop yield. The use of non-selective herbicides in-crop allows for control of weeds that are difficult to manage with selective herbicides, while minimising spray costs. Paraquat and paraquat + diquat can be used to spray weeds in the inter-row space. In Western Australia research investigating methods to control a range of weeds, particularly in the pulse phase of a rotation, identified inter-row spraying as an effective option. Hashem et al (2004) showed that Spray.Seed® used in the inter-row area of narrow-leaf lupins sown in 55-cm wide rows effectively controlled two weeds, blue lupins (Lupinus cosentinii) and wild radish (Raphanus raphanistrum) (Table T2.3a-1). Inter-row spraying of the lupin crop at the 7-leaf growth stage with Spray. Seed® at a rate of 2 L/ha gave the best lupin yield and a high level of control for both broadleaf weed species. Key benefit #2 B a n d s p r a y i n g r e d u c e s t h e r i s k o f h e r b i c i d e r es is t an c e develo pm en t by lim it in g th e applic at ion of higher risk selective herbicides over the crop row. By limiting the use of higher resistance risk herbicides to the crop-row band, only 30–50% of the field is being treated, and less selection pressure is therefore placed on the whole weed population. The remaining portion of the paddock (inter-row) is treated with either a lower risk (knockdown) herbicide or by inter-row cultivation. Crop-row weed control is important, particularly in reducing additions to the weed seedbank. Band spraying over the crop row allows selective herbicides to control weeds that the shielded sprayer or inter-row cultivation techniques cannot reach. In addition, band spraying effectively reduces the total amount of herbicide used on a per hectare basis, which in turn reduces costs and minimises the potential for herbicide carryover. Practicalities Key practicality #1 Her bic ide M OA grou ps n eed t o be r ot at ed. Since paraquat and diquat are the only knockdown herbicides registered for shielded spraying, it is essential to carefully plan (and perhaps limit) the use of these herbicides in other parts of the crop rotation. Key practicality #2 Tim ing of sh ielded spr ayin g is im portant . The range of available knockdown herbicides for shielded spraying is restricted to the bipyridyl herbicides in broadacre cropping. For this reason it is important to spray small weeds in order to maximise results from these herbicides. Key practicality #3 Care must be t aken with th e s et -u p and oper ation o f sh ielded s pr ayer s to m inim is e s pr ay dr ift . A ll shields leak spray drift to some extent. The set-up and operation of shielded sprayers is as important as the design of the shield (Rochecouste and Burgis 2003). Small amounts of a translocated herbicide such as glyphosate can damage most crops. Cotton growers using glyphosate through shields in 2001–02 reported yield losses of up to 30%. Drift from shields is decreased by reducing shield height to less than 5 cm, by using coarse droplets (BC PC classification – the British Crop Protection Table T2.3a-1 Effect of controlling blue lupin and wild radish in narrow-leaf lupins in Western Australia with Spray.Seed® at 1 L/ha and 2 L/ha at two application times (Hashem et al 2004)
Council developed an international classification system using a set of reference nozzles for comparison with manufacturers’ nozzles) and by travelling at lower speeds (Nicholls et al 2003). Contributors Warwick Felton, Di Holding and Andrew Storrie References Hashem, A., Blackwell, P. and Collins, M. (2004). Excellent weed control in wide row lupins. In Crop Updates 2004, Western Australian Department of Agriculture. Nicholls, J., Dorr, G., Woods, N., Burgis, M. and Rochecouste, J. (2003). Shields ain’t shields. CRDC-funded shielded sprayer study. Conservation Farmers Inc. Rochecouste, J. and Burgis, M. (2003). Shielded sprayers. The Conservation Farmer 4(2): 137–146. |