THROUGH A GLASS, DARKLY R. C. Kemerait; Jr. Department of Plant - - PowerPoint PPT Presentation

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THROUGH A GLASS, DARKLY R. C. Kemerait; Jr. Department of Plant - - PowerPoint PPT Presentation

Mar 12, 2023 248 likes •490 views

THROUGH A GLASS, DARKLY R. C. Kemerait; Jr. Department of Plant Pathology, The University of Georgia Cotton Incorporated Target Spot Summit Foliar Diseases of Cotton Historically considered incidental for cotton production in

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THROUGH A GLASS, DARKLY

  • R. C. Kemerait; Jr.

Department of Plant Pathology, The University of Georgia Cotton Incorporated Target Spot Summit

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Foliar Diseases of Cotton

  • Historically considered “incidental” for

cotton production in Georgia.

  • Various causes-

– E.g. Cercospora, Stemphylium, Alternaria – Stemphylium leaf spot tied to nutrient deficiencies, esp. potassium

  • Wet weather blight (Ascochyta blight)

– Phoma – Typically seen on younger plants – Rarely seen today

  • Aereolate mildew

– Ramularia – Sporadic occurrence

  • Corynespora leaf spot

– J.P. Jones 1963 – Southwest Asia- to – Include boll rots

Ascochyta wet weather blight Aereolate mildew, Appling Trial 2007

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Stemphylium Leaf Spot on Cotton

Seminole County 2009

Rome Ethredge

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Leaf Spot Disease in Attapulgus Stemphylium leaf spot 8 September 2009

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Cercospora Leaf Spot on Cotton

Colquitt County 2009

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Cercospora Leaf Spot on Cotton

Colquitt County 2009

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Fungicides for Foliar Diseases of Cotton

  • Topsin-M

– Section 18 in Florida – Specifically for hardlock – May also benefit leaf health

  • Headline (pyraclostrobin)

– Received Section 3 label in 2007 – Single application expected – Labeled for foliar disease control – “Plant Health” benefit?

  • Quadris (azoxystrobin)

– Supplemental label received in July 2008

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2007 Appling County Fungicide Trial

Photograph by Sandy Newell

Untreated Plot/Areolate Mildew

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2007 Appling County Fungicide Trial

Photograph by Sandy Newell

Pyraclostrobin mid-canopy/Areolate Mildew

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Appling County Fungicide Trial 2007

1402.7 1450.7 1449.3 1488 1386.7 250 500 750 1000 1250 1500 LINT (lb/A) Untreated Headline, 6.14 fl oz Caramba, 12 fl oz Quadris, 9.2 fl oz Topsin, 16 fl oz

A A A A A

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Two shots of Headline (6 fl oz/A) and 0 lb/A vs 180 lb/A potassium

Stemphylium leaf spot 2010

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Cotton Fungicide Studies

2004 + 2005 Tifton, 2005 + 2006 Attapulgus, 2007 Appling Co. 2 (3) Applications beginning at full bloom

  • 100
  • 50

50 TIF 2004 AT 2005 TIF 2005 AT 2006 APP 2007

Value ($/A) compared to control

Headline, 6.14 oz Headline, 9.2 oz Quadris, 6 oz Quadris, 9 oz Topsin , 16 oz Topsin, 16 oz (4) Bottom line- 10 times made a little money, 10 times lost money

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In desperation, “BOB!! It CAN’T all be potassium deficiency”

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Leaf Spot Diseases in Decatur County (likely Corynespora and/or Cercospora) 8 September 2009

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Corynespora cassiicola

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2010 Attapulgus REC, Decatur County

Stemphylium and Corynespora Leaf Spots (Affected leaves only) Fungicide programs analyzed across cotton varieties 3.4 4.4 9.8 2 4 6 8 10 Headline, 6 fl oz/A Headline, 12 fl oz/A Untreated %Leaf Area Affected Fungicide Program

August 23 2010 LSD=3.221

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2010 Attapulgus REC, Decatur County

Stemphylium and Corynespora Leaf Spots Fungicide programs analyzed across cotton varieties 3440 3413 3348 2000 2500 3000 3500 4000 Headline, 6 fl oz/A Headline, 12 fl oz/A Untreated Seed cotton (lb/A) Fungicide Program

Prob(F)=0.7285

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2010 Thomas County Field stripped with/without Headline 6 fl oz/A

RJ Byrne

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2010 Commercial Grower Trial, Thomas County

Corynespora Leaf Spot RJ Byrne, UGA Cooperative Extension

25 72 25 50 75 100 Headline, 6 fl oz/A Untreated % Defoliation Fungicide Program

P<0.05

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2010 Commercial Grower Trial, Thomas County

Corynespora Leaf Spot RJ Byrne, UGA Cooperative Extension

1318 1254 1100 1200 1300 1400 Headline, 6 fl oz/A Untreated Lint (lb/A) Fungicide Program

P<0.1

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Through a glass, darkly……

  • Stemphylium leaf spot.

– Neither disease severity nor defoliation affected by fungicides. – Yield not affected by fungicide applications. – Disease severity and defoliation significantly affected by pre‐plant application of potassium but in‐season foliar application of potassium.

  • Corynespora leaf spot disease

– Disease severity and defoliation reduced with application of fungicides. – Yields increased with application of fungicides, statistically significant (64 lb/A lint) in one trial. – Best timing….. – Best fungicides…. – Best recommendations……. – Best economics………. – Boll rots……….

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Foliar Diseases of Cotton

  • Historically considered “incidental” for

cotton production in Georgia.

  • Various causes-

– E.g. Cercospora, Stemphylium, Alternaria – Stemphylium leaf spot tied to nutrient deficiencies, esp. potassium

  • Wet weather blight (Ascochyta blight)

– Phoma – Typically seen on younger plants – Rarely seen today

  • Aereolate mildew

– Ramularia – Sporadic occurrence

  • Corynespora leaf spot

– J.P. Jones 1963 – Southwest Asia- to – Include boll rots

Ascochyta wet weather blight Aereolate mildew, Appling Trial 2007

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Acknowledgements

– BASF – Calvin Perry – Billy Mills – Jared walls – Michael Foster – Lina Young – Joy Carter – Jeannette Mixon – Benji Baldree – Jhen Bennett