Mixing SPC with water prior to application facilitates the release of HP, decreasing the time between adding the product and the HP concentration reaching the target dose. If this is impractical, treatments could be managed by assuming that the start of the exposure is when the product reaches the target dose,rather than when the product is added. In liquid SPC trials, consistent under-dosing was probably largely due to addition of the product to the system by gravity driven flow at too low a rate, particularly on farm A which had the greatest flow (34–35 L/s) and required constant addition of SPC to compensate for the diluting effect of incoming water and loss of product at the discharge point. This can be addressed by increasing the initial dose of SPC and/or by monitoring the dose during the treatment and adding additional product when required. suggested that SPC may display reduced efficacy in organically loaded systems and that higher doses would be required inthese conditions to achieve adequate efficacy. We found no evidence that using SPC in our higher organic load systems reduced the amount of available HP in the system during treatment. Monitoring dose throughout treatment should also adequately address this problem.