Assess blackspot and shatter bruise risk at harvest based on pulp temperature, soil moisture, specific gravity, drop height, vine kill timing, and cultivar.
Fill in the harvest conditions and press Assess Bruise Risk to see your risk scores and recommendations.
Blackspot bruise results from impact crushing cells beneath the intact skin. The bruise is invisible externally but appears as dark discoloration when peeled — typically 24–48 hours after impact. Shatter bruise produces visible cracks or fissures in the skin and is caused by cold, brittle tuber tissue tearing under impact. Both reduce marketable yield, but shatter is immediately visible while blackspot is discovered at the packer or processor.
V6: Each factor contributes weighted points to two separate scores — one for blackspot risk and one for shatter risk. Cultivar sensitivity scores are recalibrated against WSU Columbia Basin trial data from 2008–2019 (679 records across 13 seasons, 4 trial types). A key V6 change: harvest timing now interacts directly with cultivar shatter susceptibility — Russet Burbank, for example, shows a 4.5× increase in shatter from early to late harvest in the WSU dataset (13% early vs 59% late). Specific gravity thresholds are recalibrated to the Columbia Basin distribution (median 1.080). Tuber size is added as a shatter modifier based on the WSU size-vs-shatter gradient. Additional sources: UI BUL966, CSU Extension Fact Sheet 5.621, Hendricks & Thornton 2022 AJPR, Mosley et al. 2000.
University of Idaho Extension Bulletin 966 (Monitoring Tools for a Potato Bruise Prevention Program) is the most comprehensive free resource. WSU Extension Bulletin EB1080 covers reducing harvest bruise. Colorado State Extension Fact Sheet 5.621 covers blackspot specifically. For on-farm assessment, the iodine dip method and instrumented sphere (Smart Spud) are the most practical tools. Related calculators: Potato Storage Calculator.