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Alyssa Koehler, Ph.D.

University of Delaware

Field Crops Disease Management Update

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https://www.morningagclips.com/flooding-and-ponding-in-soybeans/

A. Collins

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Pod and Stem Blight, Stem Canker, and Phomopsis Seed Decay

• Treating seed won’t make it high quality, but can increase stand 10-15%. Seeding rate can be lowered without sacrificing stand or yield potential

• Clean seed to have less than 20% damaged seed in the lot

• Money saved from reducing seeding often pays for treating seed A. Collins

http://www.soybeanresearchinfo.com/pdf_docs/CPN1020W_fungicide_efficacy_seedling.pdf

https://www.mssoy.org/uploads/files/fungicide-efficacy-purdue.pdf

Foliar fungicide application from R3 to R5 may reduce damage and improve seed quality, may or may not impact yield.

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SDS

• Fusarium virguliforme

• No effective foliar fungicides

• iLeVO seed treatment (also has activity on SCN)

• Select resistant varieties (also select for SCN resistance)

P. Sylvester

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Fusarium Head Blight• FHB or scab

• Fusarium graminearum (Gibberella zeae)

• Sexual and asexual spores land on wheat heads and infect during flowering

• Can lead to shriveled or wilted kernels with a “tombstone” look usually contaminated with mycotoxin deoxynivalenol(DON) sometimes called vomitoxin

P. Sylvester

FHB Disease Cycle

J. Miller

Developing an Integrated Disease Management Program

• Planting Date

– plant after the Hessian fly-free date to avoid peak populations of aphids carrying Barley Yellow Dwarf Virus and to reduce infection and overwintering of foliar pathogens

• Rotational Sequence

– use rotation to reduce inoculum loads and build up

– avoid following corn with high levels of stalk rot as Fusarium-infected debris are inoculum for scab epidemics

• Variety Selection

– look for high yield, but also disease resistance

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Wheat Variety Selection • There is no total resistance, but partial resistance can slow the development or

reduce disease severity

– Fusarium head blight/scab (FHB)

– Stagonospora leaf and glume blotch

• FHB Misted Nursery Results from MD can help to inform variety selection https://psla.umd.edu/sites/psla.umd.edu/files/_docs/MD_CROPS/FHB%20Misted%20Nursery%20Factsheet-2018.pdf

Susceptible HostConduciveEnvironment

Pathogen

Disease

Multiple factors determine the incidence and severity of a disease

Disease Triangle

wheatscab.psu.eduUses weather conditions to estimate the risk of a severe outbreak of disease

Can sign up to have updates e-mailed or texted directly to you

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Fungicide Timing for FHB

• Sprays prior to flowering will not provide suppression of scab or toxin production

• Fungicides for FHB are most efficacious when applied at the start of flowering (when ~50% of main tillers are flowering)

• A spray up to one week after the beginning of flowering can offer good disease and toxin reduction

• 70-75% reduction in FHB and DON levels when using a moderately resistant wheat variety in combination with a triazole fungicide (Proline, Prosaro, Caramba) applied at Feekes 10.5.1 (~45% if using fungicides with a susceptible variety)

• Miravis Ace is offering a wider window 50% head emergence through flowering

CPN-3002-W-1

“Application of products containing strobilurin fungicides may result in elevated levels of the mycotoxin deoxynivalenol (DON) in grain damaged by headscab” …don’t apply after FGS 8

North Central Regional Committee on Management of Small Grain Diseases

Scouting for Scab in Wheat • Begin to scout 18-21 days after flower

• 10 randomly selected sites per field

– keep you head up and reach down every 5 steps

– pick a head and place in a gallon bag

– 10-20 times per site

% Incidence = # of heads with scab symptoms

total number of heads collectedX 100

• Most DON is in tombstones (scabby kernels) and chaff so if you have a significant level of scab you can increase the fan speed on your combine to try to minimize tombstones entering the bin

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Questions?

Alyssa Koehler

Carvel Research and Education Center

Georgetown, DE

akoehler@udel.edu