Foliar Fungicide Management for Corn Production

Brian JonesAgronomy Extension Agent

Outline

• Foliar corn diseases• Deciding to use fungicides• Foliar fungicides for corn

– Selection (which to use)– Timing (when to use)– Application (how to use)

• Resistance management• Do they pay?• Safety

Introduction

• Fungicide: A chemical or physical agent that kills or inhibits the growth of fungi

• Classified in terms of– Mobility in the plant (contact, systemic)– Role in protection (prevent, eradicate)– Breadth of activity (single or multi-site)– Mode of action (specific process)– Chemical group

Introduction

• Why are we talking about this?– Lots of interest– Growth in continuous corn rotations

• Most diseases over-winter on infected plant tissue• Not as big an issue in silage from year to year

– Economic issue• $2 corn: does not pay• $4 corn: might pay

Effectiveness

• Leaf diseases– Gray leaf spot– Corn leaf blight (northern and southern)– Anthracnose leaf blight– Northern corn leaf spot– Eye spot– Rust

Effectiveness

• Leaf diseases– Gray leaf spot– Northern corn leaf blight

Most important yield limiting corn diseases in the Valley

Gray Leaf Spot

• Symptoms – leaf lesions are pale brown or gray, parallel-sided and 1/16 to

1/4 x 1/4 to 2 in. – usually occurring late in the season

• Environment – warm, humid weather – July through August.

• Survival – fungus survives on crop residues and on grass weeds– spread by wind and splashing rain.

• Management – resistant hybrids – crop rotation

Gray Leaf Spot

Northern Corn Leaf Blight

• Symptoms – large leaf lesions, usually 1/2 to 11/2 inch by 2 to 6 inch – grayish green later becoming tan to grayish black

• Environment – Favored by temperatures of 65 to 78F accompanied by heavy

dews • Survival

– fungus survives on corn, corn residues and spores dispersed by wind.

– spores are air-borne long distances • Management

– resistant hybrids – crop rotation

Northern Corn Leaf Blight

Decision Process:Yield Factors

• Yield is the result of a combination of factors:– Plants per acre– Ears per plant– Rows per ear– Kernels per row– Kernel weight

Decision Process:Yield Factors

• Stress on any of these factors will lower yield

• Maximum yield potential already set at tasseling stage (VT)

• After VT, focus is completely on preserving yield potential

• Late-season stress will reduce yield potential, but NOTHING will increase potential past VT (important point)

Decision Process:Yield Factors

• Reducing stress after VT by a fungicide application may be useful to:– Aid in kernel retention– Maintain kernel weights

• Fungicide applications will only protect plants for a brief period of time

Decision Process:The Probability Ladder

Susceptible Hybrid

Continuous Corn

No-Till

Late Planting

High Yield Potential

Irrigation

Disease Activity at Tassel

Disease Favorable Weather LowerProbability

HigherProbability

(adapted from P. Vincelli, University of Kentucky)

Decision Process:Stop! Look! Consider!

• Three step process from Iowa State

• Stop!– Determine the resistance of the hybrid first

• Single biggest determining factor

– Survey looked at 68 university trials and 121 on-farm trials

• Yield advantage was greatest for highly susceptible hybrids

• Yield benefit did not cover the cost of application

Decision Process:Stop! Look! Consider!

• Stop! Look!– Most foliar diseases work up– Start scouting immediately before tasseling– If there is disease up to and including the ear

leaf before VT consider spraying• Ear leaf and above = 90% of carbohydrates for

grain fill• Must protect these leaves

Decision Process:Stop! Look! Consider!

• Stop! Look! Consider!– Environmental conditions

• Warm, humid weather (64-81)• Dry weather stops most fungi

– Planting date• Later planted corn at greater risk

– Corn on corn (high residue)• Pathogens survive winters on infected residue

Decision Process:Stop! Look! Consider!

• Stop! Look! Consider!– Fungicide activity

• Most are effective for 14 to 21 days• Corn takes about 60 days from silk to maturity• Don’t spray too early!

– Stalk rots• No effect on stalk rots (directly)• However, leaf diseases reduce photosynthesis and

increase susceptibility

Fungicide Selection and Use

• Many fungicides labeled• Should focus on systemics (avoid contacts)

– Not enough residual to be effective

• Primary class are the strobilurin fungicides– Azoxystrobin (Quadris, pre-mix with propiconazole in

Quilt)– Pyraclostrobin (Headline)– Trifloxystrobin (pre-mix with propiconazole in

Stratego)

Fungicide Selection and Use

FungicideApplication Rate (fl

oz/acre)Application Timing

Ground Air Ground Air

Headline® 6-12Prior to disease

developmentNIS @ 1

pt/100 galCOC @ 1

pt/acre 20 2-5

Quadris® 6-15.5Prior to disease

developmentNIS @ 1

pt/100 galCOC @ 1

pt/acre 20 5

Quilt® 7-14At onset of disease to

brown silkNIS @ 1

pt/100 galCOC @ 1

pt/acre 20 2-5

Stratego® 7-12

At onset of disease through end of silking

(R2)NIS @ 1

pt/100 galCOC @ 1

pt/acre 10 2-5

Adjuvants Coverage (gpa)

(adapted from Elmore and Abendroth, Iowa State University)

Restrictions

(adapted from Dorrance et al., Ohio State University)

Mycotoxin Control?

• Foliar fungi are not mycotoxin producers

• Control may impact mold development– Maximizing photosynthesis– Delay cannibalization of stalk nutrients– Reduce susceptibility of stalk to disease

• Studies from Wisconsin shown a tendency toward improved silage yield and milk/acre

Resistance Management

• Fungicides are the quickest pesticides to develop resistance– Multiply extremely rapidly– Very specific MOA

• Avoid spraying for “plant health” reasons– Do not spray unless a disease threshold has

been met

Do Fungicides Pay?

• Virginia Tech Trials 2006:– 6 sites in eastern VA on grain– Comparing Quadris and Headline against

untreated checks– No yield advantage observed– No significant disease pressure observed

(2006 Virginia On-Farm Corn Test Plots, VCE Publication 424-038)

Do Fungicides Pay?

• University of Nebraska-Lincoln 2005-2006

(http://cropwatch.unl.edu/archives/2007/crop18/corn_fungicides.htm)

No significant differences

•Asgrow RX 752 YG•Mild gray leaf spot•Negligible common rust

Do Fungicides Pay?• University of Nebraska-Lincoln 2005-2006

(http://cropwatch.unl.edu/archives/2007/crop18/corn_fungicides.htm)

•Moderate/severe gray leaf spot and rust

Do Fungicides Pay?

• University of Illinois

(adapted from E. Nafziger, The Bulletin No. 14 June 29, 2007)

Average yield increase = 6.2 bu/acBarely covers costs at $4 corn

Using Safely

•Follow the label, the label is the law•Pay attention to PPE requirement•Pay attention to PHI and re-entry

THANK YOU

Questions?

brjones8@vt.edu

http://www.valleycrops.cses.vt.edu