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How to scout for plant diseases • USDA-APHIS-PPQ-National Seed Health System phytosanitary inspection reference – http://www.seedhealth.org/standardization/ RMB0402.pdf How do I start? • Look the field over: are there any spots you should focus on? (depends on what you’re looking for) – Low areas – Edges – Microclimates • Decide on a sampling pattern • Scout at the appropriate growth stage for the disease of interest • Note symptoms and signs • Get samples properly diagnosed if needed “Stagger X pattern” “Equidistant passes pattern” Patterns of plant disease Regular x x x x x x x x Random x x x x x x x x x x x x x xx x x Clustered x xx x xx x x x x x xx Examples: Wind-borne Seed-borne - Rusts Stubble-borne Contaminated potato seed pieces Irrigation lines (nozzles) xxxx x xx x Soil-borne (foci) Nematodes Sampling patterns x x x x x x x x x x x x x x x x x x x x x x x x x xx x xx x x x x x xx xxxx x xx x Other sampling patterns (take a sample in each quadrat) “Arbitrary” vs. “Random” • Arbitrary: choose plants as walk along pattern, perhaps at even intervals like ‘every 3 steps’ • Random: must use a random number generator or other random method to select plants (eg. numbers in a hat) How many samples should I take? “minimum of 95% confidence level in detecting an infection level of 0.1%”