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23SUMMER 2015 SPUDSMART.COM therefore to keep an eye out for signs of disease when sorting seed pieces throwing out tubers with significant lesions. Applying a chemical seed piece treatment that prevents ungerminated scurf spores from becoming active is another important control option. Though seed treatments have been shown to be effective at reducing silver scurf they will not completely prevent infection of daughter tubers particularly if the seed infection is severe. The silver scurf pathogen can also live in the soil for up to two years so the optimal way to break up the life cycle of H. solani is to rotate crops. If you are practicing a good three-year crop rotation with two years between potatoes you shouldnt see soilborne spores as a real source of inoculum for silver scurf says Shinners-Carnelley. LIMITING INOCULUM While silver scurf can develop on potatoes below ground while the plants are growing its at harvest time and afterwards that the real trouble usually starts. Shinners-Carnelley stresses the importance of minimizing the amount of time that potatoes spend in the field after vine death and skin set since silver scurf severity and damage increase the longer tubers are left in the ground. If tubers are sitting there and the tops have gone down this is the window of time when the infection risk of silver scurf really increases. And if that happens in the field it means youre bringing a higher level of disease into the bin she says. Once inside that storage you can have many disease cycles occur and as more occur of course the overall amount of silver scurf that you see will continue to increase Shinners-Carnelley adds. The reality is the conditions in the storage can be very conducive to having the disease develop so really you need to focus on other management strategies that help limit the amount of inoculum thats going into the bin. Shinners-Carnelley says one such strategy is reducing the amount of soil going into storage. When youre bringing potatoes into the bin youre also potentially bringing in a lot of soil and in a scenario like that there can be spores within that soil that can also be the source of inoculum. STORAGE CONDITIONS When infected tubers are put into storage the silver scurf lesions sporulate producing inoculum for secondary infections that can given the right conditions spread quickly throughout the bin. According to Shinners-Carnelley H. solani does best when relative humidity is above 90 per cent and temperatures are above 3 C. The same fundamental principals are in place whether its in the field or its in the bin. Your combination of temperature and moisture and Jeanette Gaultier from Manitoba Agriculture Food and Rural Development collaborated on the phosphorus acid storage study led by Tracy Shinners- Carnelley in 2009-10. ALL PHOTOS TRACY SHINNERS-CARNELLEY. If you are practicing a good three-year crop rotation with two years between potatoes you shouldnt see soilborne spores as a real source of inoculum for silver scurf. TRACY SHINNERS-CARNELLEY