Chemical residue in boom sprays poses an ever present risk requiring constant management and attention. Of particular concern are residues of sulfonylurea (SU) herbicides, which have the potential to cause significant damage to canola crops, even at very low concentrations. The cost and time involved with decontaminating a boom spray, is insignificant compared with the potential crop losses that could occur.
There were a number of incidents during 2012 where canola crops were damaged by SU residues. Most cases involved experienced operators who have not had issues in the past. In some cases, the crop damage occurred over a number of loads being applied days or weeks after the boom spray had been decontaminated. In all cases, Status (Clethodim) was being applied to canola crops. Status contains a high level of solvent which can extract SU residues from lines, tanks and filters into solution, which at very low concentrations can cause damage.
Experience indicates that allowing residues of SU herbicides to dry in the tank and lines, makes them much more difficult to remove. Ideally, spray equipment should be decontaminated immediately following the use of an SU herbicide.
This is not always practical where SU’s are being applied over an extended period of time. At the very least, equipment should be thoroughly flushed with water immediately following each application of SU herbicide.
Effective rinsing ensures that all dead ends, nozzles and filters are thoroughly rinsed, with these areas left containing water to ensure that the SU residue cannot dry in the lines. At the earliest possible opportunity, a full decontamination should be carried out.
Spraying pasture paddocks with insecticides or other products containing high levels of solvent, is not a substitute for decontamination. However should the opportunity arise, this practice prior to applying grass selective herbicides to canola, may help to reduce the risk of crop damage.
Decontamination of booms from SU herbicides requires the use of a Chlorine based product. The concentration of Chlorine in such products should be outlined on the product label in g/kg or g/L. Granular products are preferred, as they are more stable. Liquid Chlorine has a limited shelf life once opened.
Following are some common Chlorine based products that are used for decontaminating boom sprays:
Thorough cleaning involves taking the following steps:
- Drain tank and hoses and flush with water.
- Fill tank and add Chlorine based product, flush and allow to stand for at least 15 minutes.
- Repeat step 2.
- Remove nozzles, screens and filters and thoroughly clean or replace with clean components.
- Pay particular attention to dead ends, taps, recycling lines or other areas where product may be trapped or where rinsing may be less effective.
Cleaning herbicides other than SU’s requires a similar procedure. Chlorine is not always necessary, however products such as Boomblitz and Nufarm Tank and Equipment cleaner can be used. A full guide to decontaminating Boom Sprays can be found on page 20 of “Weed Control In Winter Crops”, produced by NSW DPI. This can be downloaded at the following address.