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Seed managementAvoiding blackleg issues

Seed managementAvoiding blackleg issues

John Sarup

SAC

Avoiding blackleg issuesAvoiding blackleg issues

• Blackleg control requires all-year roundattention to detail

• Both seed growers and purchasers of seedhave responsibilities

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Facing up to blacklegFacing up to blackleg

From storage to planting

•Relationship between contamination andblackleg (Seed grower issue)

•Risks at grading and bagging (Seed growerissue)

•Risks on receipt (Ware grower issue)

•Risks at planting (Ware grower issue)

•Conclusions

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The more seed is contaminated withPb the greater the risk of blacklegThe more seed is contaminated withPb the greater the risk of blackleg

SAC resultsDesiree

SAC Blackleg testthresholds

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AverageEca /tuber

in test

Growing conditions

Good Average Poor

0 – 2.5 Low Low Slight

2.6 – 4 Slight Slight/moderate

Moderate/High

> 4 Slight/moderate

Moderate/High

High

Blackleg risk assessmentsScotland 2010/11

Blackleg risk assessmentsScotland 2010/11

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21% stocks>log102.5

Samples of sound tubers

Blackleg risk assessments are only snapshots in time – Contamination

can increased through poor storage and poor handling at or after grading

Good storage results in adecline in contaminationGood storage results in adecline in contamination

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But condensation late in storage can increase condensation

Increase in condensationlate in storage

But soft rotted tubers were more frequently

present in seed stocks in 2010/11

Contamination from soft rotsOne factor contributing to increased blackleg in 2011

Contamination from soft rotsOne factor contributing to increased blackleg in 2011

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At grading 1 rotten tuber can contaminate 100’s more

Elphinstone & Perombelon, 1986

One rotten tuber is still contaminatingtubers after >600kg is passed over graderOne rotten tuber is still contaminatingtubers after >600kg is passed over grader

8Elphinstone & Perombelon, 1986

Judging risk with soft rotsJudging risk with soft rots

Look at top surface of boxes to be graded

• < 1 watery soft rot - picking off from the tippler face or exitfrom the hopper should restrict bacterial spread toacceptable levels

• 1 - 5 watery soft rots - high risk of bacterial spread. Withblackleg susceptible varieties, put more pickers at thetippler face or hopper exit. Some spread will occur butmake big efforts to ventilate bags or boxes after grading torapidly dry any surface moisture

• > 5 watery soft rots - where possible avoid grading andreturn the affected boxes to a positive ventilation system

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Putting damp tubers into polypropsacks – can increase contaminationPutting damp tubers into polypropsacks – can increase contamination

• Besides condensation,dampness comes from:

– Damage

– Expression of moisture duringgrading

– Liquid from seed treatmentapplication

– De-sprouting

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Putting damp tubers into polypropsacks – can increase contaminationPutting damp tubers into polypropsacks – can increase contamination

• Allow as much airmovement aroundpolyprop bags aspossible

– Stack apart

– Place on pallets

– Ventilate air roundbags

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Buyers of seed haveresponsibilities alsoBuyers of seed haveresponsibilities also

• Handling seed correctly after receipt isimportant

– Decant from polypropbags

– Ventilate with cool air

– Restrict sprout growth

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Buyers of seed haveresponsibilities alsoBuyers of seed haveresponsibilities also

• Reducing blackleg is achieved by:

– Avoiding de-sprouting at planting

– Controlling other seed-borne diseases suchas Rhizoctonia

– Planting into warm (7oC +) seed-beds

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Avoiding blackleg issuesAvoiding blackleg issues

• Take care to avoid increasing contaminationat grading and bag filling

• Pick off rots early on the grading line

• Disinfect or clean grader after a diseasedstock

• Ventilate polyprop bags after filling

• Alert staff how to handle seed on arrival

• Ventilate seed to remove condensation andheat of respiration

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