1. Foliar Fungicide Management for Corn Production Brian Jones Agronomy Extension Agent

2. 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

3. 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

4. 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

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

6. Effectiveness Leaf diseases –Gray leaf spot –Northern corn leaf blight Most important yield limiting corn diseases in the Valley

7. 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

8. Gray Leaf Spot

9. 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

10. Northern Corn Leaf Blight

11. 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

12. 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)

13. 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

14. Decision Process: The Probability Ladder Susceptible Hybrid Continuous Corn No-Till Late Planting High Yield Potential Irrigation Disease Activity at Tassel Disease Favorable Weather Lower Probability Higher Probability (adapted from P. Vincelli, University of Kentucky)

15. 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

16. 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

17. 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

18. 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

19. 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)

20. Fungicide Selection and Use (adapted from Elmore and Abendroth, Iowa State University)

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

22. 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

23. 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

24. 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)

25. 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

26. 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

27. Do Fungicides Pay? University of Illinois (adapted from E. Nafziger, The Bulletin No. 14 June 29, 2007) Average yield increase = 6.2 bu/ac Barely covers costs at $4 corn

28. Using Safely Follow the label, the label is the law Pay attention to PPE requirement Pay attention to PHI and re-entry

29. THANK YOU Questions? brjones8@vt.edu http://www.valleycrops.cses.vt.edu