Late Season Salvage Spraying and Crop Desiccation

PIC - Crop Spraying 2.jpg

Due to the very wet conditions in July and August, some paddocks were not able to be sprayed with their required early post emergent herbicides. While the dryer conditions in the latter half of August allowed many paddocks to be sprayed, some have remained too wet, while crop and weed growth restrictions have limited herbicide options. This has led to greater numbers of weeds present in crops than normal. The wet weather has also allowed late germinating weeds to survive and potentially set significant quantities of seed. Paddocks with problematic weeds, may require a late salvage spray or pre-harvest desiccation to limit seed set of these weeds. 

Wild Radish and Annual Ryegrass are the two priority weeds where a salvage spray or desiccation may be required, as one seed set event can lead to significant replenishment of the seed bank, requiring ongoing control for subsequent years. However, a range of other weeds may need to be controlled, particularly when green weeds or immature heads disrupt harvesting operations. 

Salvage sprays are those applied late in the growth stage of the crop, but prior to senescence/physiological maturity. These are selective sprays that target the weeds, with limited negative effect on the crop when applied correctly, allowing full grain development to occur. 

Desiccation is used both as a weed control tactic as well as a harvest aid, as it evens maturity of the crop and dries down weeds or late maturing heads to allow earlier harvesting. Desiccation occurs later than salvage spraying, because the crop needs to have reached physiological maturity as non-selective herbicides are used, killing, or severely damaging the crop in the process.  

When used for weed control, the herbicide utilises a combination of killing weeds outright plus sterilising the developing weed seed. Therefore, the timing of application is very critical. An application too early may lead to premature crop senescence and potentially significant yield penalties, while an application too late may occur after weeds have developed viable seed. 

Therefore, earlier maturing crops such as canola and barley are much better suited to desiccation than wheat, as weeds, particularly Annual Ryegrass have set seed by the time the crop is at the correct growth stage. There are very few circumstances where both the weeds and the wheat crop are in the correct growth stage for successful weed control. 

Careful consideration needs to go into each paddock that is desiccated, as there are some grain marketing limitations on desiccated crops. An example of this is desiccated barley being excluded from Malt classification. Also, seed cannot be retained from desiccated crops, as the herbicide can significantly reduce the viability of the seed. 

The following table shows some salvage spraying and desiccation options, available for the most common crops grown.

Fred Broughton