This effect is much more noticeable in Albus compared to narrow-leafed lupin, as was noted in previous glasshouse experiments. Large plot experiments with big buffers or a modelling approach would be required to quantify this yield advantage. It seems that the additional benefits of using carbendazim over thiram would be unlikely to cover the additional cost involved for narrow-leafed lupin, particularly the more resistant varieties. However, with Kiev Mutant there could be a benefit in some situations. This has to be weighed up against a small but real risk of reduced germination in some situations.
More work is needed to find out the situation of carbendazim versus thiram for yellow lupins.
Note that some products are not coloured. Thiram and Carbendazim give no control of brown spot. Fungicide seed dressings can be antagonistic to the rhizobium used to inoculate lupins. Note that caution is required with carbendazim. In one Agriculture Western Australia trial and in some South African and USA trials, crop emergence has been reduced.