Management of southern rust and frogeye leaf spot. Dr. Carl A. Bradley, University of Kentucky

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1 Management of southern rust and frogeye leaf spot Dr. Carl A. Bradley, University of Kentucky

2 Southern rust of corn

3 New Southern Rust Extension Publication Crop Protection Network Source for multi-state extension publications New southern rust publication became available in July 2017 Publications available at: cropprotectionnetwork.org

4 Southern rust of corn Caused by the fungus Puccinia polysora Not to be confused with common rust, which is caused by Puccinia sorghi Was one of the primary corn diseases present in the tri-state region in 2015 and 2016 Prevalent in 2017 too, but hot dry weather slowed it down

5 Southern rust of corn The southern rust fungus DOES NOT overwinter in Kentucky or the region (or really much in the U.S. at all) The fungus has to survive on a living host year-round (obligate parasite) Where does it overwinter? Mexico and Central America in regions where corn is grown year-round How does it get to Kentucky and this region? Weather systems push spores northward via the Puccinia Pathway Infections occur along the way, creating additional spores

6 Puccinia Pathways Image courtesy USDA-ARS

7 Common Rust (Puccinia sorghi) Southern Rust (Puccinia polysora)

8 Southern rust upperside of leaf underside of leaf

9 Common Southern

10 Southern rust: a potentially explosive disease Over 1,300 pustules in this picture (one partial leaf) Up to about 5,000 spores can be produced per pustule One pustule with 5,000 spores inside

11 Explosive disease 5,000 spores per pustule 1,300 pustules per leaf 15 leaves per plant 26,000 plants per acre >2.5 trillion spores per acre Repeating cycles: Only takes about 10 days from infection to production of additional spores

12 Fungicide Management of southern rust

13 Dixon Springs, IL R1 No Fungicide

14 Dixon Springs, IL 2009 Southern Corn Rust Infestation Applications made at R1 (silking)

15 2015 Corn foliar fungicide trial Princeton, KY 3 fungicide application timings R3 (milk) R4 (dough) R5 (denting)

16 R3 July 21, 2015

17 R4 July 27, 2015

18 R5 August 10, 2015

19 Relative yield response (bu/a) Princeton, KY Southern rust first observed on July 28th R3 (milk) R4 (dough) R5 (denting) Growth Stage (7/21) (7/27) (8/10)

20 Non-treated R3 application Southern rust had limited impact on yield in 2015 (arrived too late relative to the corn growth stage) R4 application in this trial. R5 application Gray leaf spot was the primary culprit.

21 Relative yield response (bu/a) Princeton, KY Southern rust first observed on July 18th R1 (silking) R3 (milk) R4 (dough) Growth Stage (7/8) (7/25) (8/3)

22 How late is too late? Crop stage when southern rust first detected Vegetative VT (tasseling) R1 (silking) R2 (blister) R3 (milk) R4 (dough) R5 (dent) R6 (black layer) Possible benefit from spraying Not likely to find southern rust at this stage unless corn is planted very late Yes Yes Yes Yes Maybe, with severe disease pressure Unlikely No From new southern rust publication at

23 Southern rust of corn Management: Unfortunately, nearly all corn hybrids are susceptible, so risk of yield loss is present if disease shows up early enough Know the whereabouts of southern rust Kentucky Pest News, UK Grain Crops Blog, The Bulletin, ipipe Apply a foliar fungicide at the right timing, if the risk warrants it

24 Southern rust tracking on the ipipe system: ext.ipipe.org

25 Southern rust tracking: ext.ipipe.org

26 Where do these observations come from? Extension specialists and diagnostic labs from each state Tweets! Searched Twitter for tweets about southern rust Observations from non-university/extension sources were yellow (suspect) until confirmed by University/Extension sources

27 Using Twitter to track southern rust Twitter Twitter users tweet: picture of disease, disease name, and county and state in which it was found ipipe system (integrated pest information platform for extension and education) was used to upload these findings onto an observation map (funded by a grant from the USDA-NIFA)

28 Frogeye leaf spot of soybean

29 Frogeye leaf spot of soybean The most damaging foliar disease of soybean that regularly occurs in Kentucky and this region Favorable conditions include, wet, warm, and humid weather

30 Sporulating lesions

31

32 2010 IL KY TN G. Zhang et al. (2012) Plant Dis. 96:767 Research funded by the Illinois Soybean Association

33 IL MO KY TN AR MS LA AL IN NC Confirmations of QoIresistant Cercospora sojina isolates were made by the Bradley lab (Univ. Illinois), or the Kelly lab (Univ. Tennessee). Soybean leaf samples were collected by university and extension plant pathologists from several states. Research funded by the United Soybean Board

34 Soybean Fungicide Trials Fungicides applied at R3 (beginning pod) Frogeye leaf spot-susceptible variety used Severe frogeye leaf spot pressure

35 FLS severity (%) Princeton, KY 2015 IL KY QoI LSD 0.05 = MBC QoI MBC QoI SDHI QoI QoI QoI 10 0

36 Non-treated

37 Headline

38 TopGuard

39 Non-treated

40 Headline

41 TopGuard

42 Yield (bu/a) Princeton, KY LSD 0.05 = 5.4 MBC QoI MBC QoI SDHI QoI QoI QoI 40 QoI

43 FLS severity (%) Princeton, KY 2016 IL KY QoI LSD 0.05 = MBC QoI MBC QoI SDHI QoI QoI QoI

44 Yield (bu/a) Princeton, KY LSD 0.05 = 7.4 QoI MBC QoI MBC QoI SDHI QoI QoI QoI

45 FLS severity (%) Dixon Springs, IL 2015 IL KY LSD 0.05 = QoI MBC QoI MBC QoI SDHI QoI QoI QoI 0

46 Yield (bu/a) Dixon Springs, IL QoI MBC QoI MBC LSD 0.05 = 6.1 QoI SDHI QoI QoI QoI

47 Soybean Variety X Fungicide Trial Funded by the Kentucky Soybean Promotion Board Five locations in which frogeye leaf spot was rated Locations managed by Univ. KY Soybean Performance Variety Trials Coordinator (Dr. Claire Venard) Butler Co. Caldwell Co. Calloway Co. Fayette Co. Hancock Co.

48 Soybean Variety X Fungicide Trial Three fungicide treatments: Non-treated Headline (solo strobilurin product) Quadris Top (strobilurin triazole product)

49 Frogeye leaf spot severity (%) Frogeye leaf spot severity across all locations Nontreated Headline Quadris Top 60 LSD 0.05 = * 0 Susc Mod Res Res

50 Yield (bu/a) Yield across all locations Nontreated Headline Quadris Top * LSD 0.05 = Susc Mod Res Res

51 Summary The solo strobilurin product did not significantly reduce frogeye leaf spot compared to the nontreated control Due to fungicide resistance In general, the largest yield response to fungicides occurred on frogeye leaf spot-susceptible varieties

52 Fungicide is not the only way.. Frogeye leaf spot can also be managed by growing resistant soybean varieties Soybean varieties that contain the Rcs3 gene will be resistant to all known races of the fungus that occur in the U.S.

53 UK Soybean Variety Testing Trial Calloway Co., KY

54 KYgrains.info

55 Thanks for your attention!

56 Fungicide studies in Southern IL, : stalk rot and foliar diseases Belleville (SW IL), Dixon Springs, IL (SE IL) Headline fungicide (9 fl oz) vs. Non-treated Evaluated stalk rot when kernels were at black layer stage Belleville Dixon Springs

57 A 5 is a 4 that is lodged due to stalk rot. Photo by Ron Hines

58 Stalk rot severity (0-5) Ear leaf severity (%) Fungicide Effect on Stalk Rot Nontreated Fungicide A B B B Belleville Dixon Springs Location Nontreated Fungicide A B B B Belleville Dixon Springs Location

59 Disease Pressure at Belleville, IL (Primarily Southern Rust) Untreated VT

60 Fungicide Effect on Stalk Rot 2009 A A B B B B B B

61 Fungicides and stalk rots Conclusions: When foliar disease pressure was high, fungicides controlled foliar disease No direct control of stalk rot pathogens with foliar fungicides, but by allowing leaves to keep photosynthesis rates, it decreased cannibalization of stalks, which reduced the presence of stalk rot