Posted: 10/08/2015 at 06:33
There are any number of chemical fungicides. The best one I ever used - on tomatoes, against diseases like Early Blight, so it would work on spuds too - is a Chlorothalonil-based product called Daconil (although there are other brand names). It's a chemical but not toxic to fossicking insects. Some organic growers in the USA even look kindly on it.
It's available in the USA in volumes suitable for the home garden. A couple of years before I left Australia it was only available there in industrial quantities. A group of us tomato-growing friends chipped in to buy a quantity and we divided it up between us. Worked brilliantly. It's not available here in Italy in volumes for the home garden and, last time I checked, ditto the UK.