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