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 Random Clustered 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 x x x x x Examples: Wind-borne - Rusts Contaminated Seed-borne Stubble-borne potato seed pieces Irrigation lines (nozzles) x xx xx xx x 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 x x x x x x x xx xx xx x 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%”