foliar fungicide management for corn production brian jones agronomy extension agent
TRANSCRIPT
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
