1. Crop Disease Update – August 23, 2016
Dr. Carl A. Bradley, University of Kentucky

2. Southern rust of corn

3. scr.ipmpipe.org

4. scr.ipmpipe.org

5. scr.ipmpipe.org

6. scr.ipmpipe.org

7. Southern rust effects on yield
Depends on when rust began to infect relative to the growth stage of the plant
My general observations (from fungicide trials in Illinois and Kentucky):
If southern rust is already present at tassel emergence/silking, then there is a high probability that a fungicide will be worthwhile
If southern rust does not appear until after R3 (milk), then yield will not likely be impacted enough to make a fungicide application worthwhile

8. Dixon Springs, IL – 2009 Southern Corn Rust Infestation
Applications made at R1 (silking) – rust was already present at low levels when fungicides were applied

9. 2015 Corn foliar fungicide trial – Princeton, KY
3 fungicides
Headline AMP, Quilt Xcel, Stratego YLD
3 application timings
R3 (milk)
R4 (dough)
R5 (denting)

10. R3 – July 21

11. R4 – July 27
Southern rust was just beginning to show up at this stage

12. R5 – August 10

13. Princeton, KY – 2015

14. Princeton, KY – 2015

15. Non-treated
Headline AMP – R3
Headline AMP – R4
Headline AMP – R5

16. Gray leaf spot was the primary culprit.
Non-treated
Headline AMP – R3
Southern rust had limited impact on yield (arrived too late relative to the corn growth stage) in this trial.
Gray leaf spot was the primary culprit.
Headline AMP – R4
Headline AMP – R5

17. Main questions about southern rust right now
How late is too late to spray a fungicide?
Corn for grain and silage
If corn is at R4 (dough) or R5 (denting), then it is highly unlikely that a fungicide application would be profitable. Also, could be getting close to preharvest intervals for some fungicides.

18. Main questions about southern rust right now
How late is too late to spray a fungicide?
Corn for grain and silage
If corn is at R4 (dough) or R5 (denting), then it is highly unlikely that a fungicide application would be profitable. Also, could be getting close to preharvest intervals for some fungicides.
Effect on yield?
Corn planted in April….probably minimal effect. Late- planted corn could be impacted.

19. Main questions about southern rust right now
How late is too late to spray a fungicide?
Corn for grain and silage
If corn is at R4 (dough) or R5 (denting), then it is highly unlikely that a fungicide application would be profitable. Also, could be getting close to preharvest intervals for some fungicides.
Effect on yield?
Corn planted in April….probably minimal effect. Late- planted corn could be impacted.
Effect on stalk integrity?
Similar to yield effects - it would come down to when rust arrived relative to growth stage.

20. Questions that may come up in near future
Is it safe to use southern rust-infested corn for silage or grain for feeding livestock?
There are no toxins produced by the southern rust fungus, but molds that can produce toxins could potentially grow on kernels of corn that died prematurely….bottom line is to have “risky” grain or silage tested for mycotoxins at a lab
Is it safe to breathe in the large amount of southern rust spores that are likely to get into the air during harvest?
Not toxic, but would be as dangerous as breathing in a large amount of dust (consider wearing dust mask)

21. Diplodia ear rot of corn

22. Diplodia ear rot
Has been observed in KY this year (not sure how widespread or how severe)
More likely to occur:
When rainfall occurs during silking (especially when preceded by a dry period)
In fields with a lot of corn residue (corn-on-corn, no-till)

23. “Bleached” husk leaves Infection usually starts at base of ear

24. Pycnidia (black fungal structures) on side of kernels

25. Potential impact of Diplodia ear rot
Reduced yield
Reduced test weight
Increased foreign matter (kernels don’t separate from cob, leaving pieces of cob with grain)
Mycotoxins associated with Diplodia ear rot have not yet been a problem in the U.S.

26. Diplodia ear rot
What could have been done to prevent/manage the disease?
Some foliar fungicides have Diplodia ear rot on their label, but control has been inconsistent in university research trials
Hybrids can differ in their susceptibility to Diplodia ear rot, but information is not always readily available on every hybrid
Crop rotation (avoiding corn-on-corn situations will reduce buildup of inoculum)

27. Diplodia ear rot Can anything be done now to slow down ear rot?
Harvesting early and drying down (to below 15% moisture) will prevent additional fungal growth and spread

28. Gibberella ear rot
Don White, Univ. IL
I have not yet observed this on corn in KY in 2016, but could potentially be in some fields based on the weather we’ve had
Pink to red fungal growth on kernels, generally beginning at the tip
Same fungus that causes head scab on wheat
Can produce the mycotoxins deoxynivalenol (DON, vomitoxin) and zearalenone
Don White, Univ. IL

29. Other corn diseases showing up now
Anthracnose stalk rot (tip die-back)
Diplodia leaf streak
Northern leaf blight?
Others?

30. Anthracnose stalk rot – Tip die-back and premature death
Premature plant death – sometimes ABOVE the ear while lower plant stays green
Anthracnose stalk rot –
Tip die-back and premature death

31. Anthracnose stalk rot –
Again – several internodes
Anthracnose stalk rot –
Black shiny discoloration on stalk and rotting of pith

32. Diplodia leaf streak – don’t confuse with northern leaf blight

33. Frogeye leaf spot of soybean

34. Frogeye leaf spot
Very severe on some varieties in western Kentucky this year
Not all varieties are susceptible – some are completely resistant

35. Frogeye leaf spot
Very severe on some varieties in western Kentucky this year
Not all varieties are susceptible – some are completely resistant
Is it too late to spray?
R3 (beginning pod) has shown to be the best timing for protecting against frogeye leaf spot at a critical time (disease usually is usually at low levels at R3, but can increase rapidly after R3)

36. Frogeye leaf spot
Very severe on some varieties in western Kentucky this year
Not all varieties are susceptible – some are completely resistant
Is it too late to spray?
R3 (beginning pod) has shown to be the best timing for protecting against frogeye leaf spot at a critical time (disease usually is usually at low levels at R3, but can increase rapidly after R3)
Should I spray double-crop soybeans?
Make same considerations as full-season soybeans. Is variety susceptible to frogeye? Is frogeye present? What is yield potential?

37. 2015 Soybean Fungicide Trials (Full-season soybeans)
2 locations
Princeton, KY
Dixon Springs, IL
Fungicides applied at R3 (beginning pod)
Heavy frogeye leaf spot pressure (susceptible variety)

38. Princeton, KY – 2015
LSD 0.05 = 3.6

39. Princeton, KY – 2015
LSD 0.05 = 5.4

40. Dixon Springs, IL – 2015
LSD 0.05 = 4.6

41. Dixon Springs, IL – 2015
LSD 0.05 = 6.1

42. UK Soybean Variety Testing Trial – Murray, KY

43. KYgrains.info

44. Other soybean diseases showing up now
Sudden death syndrome
Phytophthora root rot
Downy mildew
Soybean rust not here yet, but will probably show up later
Others?

45. Soybean rust observations
sbr.ipmpipe.org
Soybean rust observations

46. Thanks for your attention!