The Influence of Powdery S U Mildew on Pecan Nut Quality A g C - - PowerPoint PPT Presentation

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The Influence of Powdery S U Mildew on Pecan Nut Quality A g C - - PowerPoint PPT Presentation

Dec 30, 2023 355 likes •888 views

L The Influence of Powdery S U Mildew on Pecan Nut Quality A g C Charles J. Graham e n Pecan Research/Extension Station t e r L S U A g C e n t e r Pecan Scab L S U A g C e n t e r Several diseases at same time.

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The Influence of Powdery Mildew on Pecan Nut Quality

Charles J. Graham

Pecan Research/Extension Station

L S U A g C e n t e r

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Pecan Scab

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Several diseases at same time.

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STUART PECAN

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POWDERY MILDEW

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Powdery Mildew

The fungus Microsphaera penicillata (Wallr.:Fr.) Lev causes powdery mildew of pecan. On pecan, powdery mildew primarily appears mid‐to‐late season and will generally only affect fruit, but can be found on leaflets occasionally. Powdery mildew can occur sporadically and may not be present each year.

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Powdery Mildew

Gottwald et al. (1984) found that powdery mildew had no effect on net photosynthesis or dark respiration of nuts, but 50% coverage on the shuck reduced kernel oil, protein, and free fatty acids.

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Powdery Mildew

Brenneman and Bertrand (1989) reported that disease levels were significantly negatively correlated with kernel weight, but the percent fill of nuts were not correlated with disease severity.

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Powdery Mildew

Olsen et al. (2003) reported no significant differences in nut weight, kernel weight, percent fill, or kernel color ratings on infected and non-infected ‘Wichita’ and ‘Western’ pecan varieties.

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L S U A g C e n t e r

Pecan Cultivars Susceptible to Powdery Mildew

  • Curtis
  • Desirable
  • Farley
  • Moore
  • Pabst
  • Wichita
  • Western
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Initial infection

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Advanced infection

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SHUCK DECLINE

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Shuck Decline Stem-end Shuck Dieback Blight Tulip Disease

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L S U A g C e n t e r

Pecan Cultivars Most Susceptible to Shuck Decline

  • Success
  • Desirable
  • Forkert
  • Choctaw
  • Pawnee
  • Oconee
  • Creek
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TEST CONDITIONS

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Orchard Description

  • Orchard planted in 2005.
  • Six cultivars: Caddo, Desirable, Elliott,

Nacono, Oconee, Pawnee

  • Only 4 fungicide applications:

Prophyte, Elast, Super Tin, Agri-fos

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L S U A g C e n t e r

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Data Collection

  • 25 random nuts of uninfected,

powdery mildew infected, and with shuck decline symptoms collected from each individual tree.

  • Four replicant trees for each cultivar.
  • Individual nut length, nut diameter,

nut weight, kernel weight, oil content.

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RESULTS

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Desirable

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‘Desirable’ Pecan

TRT Length Width Control 44.27 a 24.22 a

  • P. Mildew

42.92 b 23.84 a Shuck Decline 42.95 b 23.91 a

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L S U A g C e n t e r

‘Desirable’ Pecan

TRT Nut Kernel Percent Weight Weight Kernel Control 10.29 a 5.48 a 53.17 b

  • P. Mildew

9.47 b 5.20 b 54.85 a Shuck Decline 9.67 b 5.26 ab 54.32 ab

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L S U A g C e n t e r

‘Desirable’ Pecan

TRT Nuts/lb % Oil Control 44 a 67 a

  • P. Mildew

48 b 64 a Shuck Decline 47 b 62 a

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Oconee

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‘Oconee’ Pecan

TRT Length Width Control 48.74 a 22.54 a

  • P. Mildew

48.08 a 22.21 b Shuck Decline 47.20 a 22.09 b

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L S U A g C e n t e r

‘Oconee’ Pecan

TRT Nut Kernel Percent Weight Weight Kernel Control 9.79 a 5.69 a 57.83 a

  • P. Mildew

9.12 b 5.32 b 58.02 a Shuck Decline 8.67 b 4.98 b 57.23 a

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L S U A g C e n t e r

‘Oconee’ Pecan

TRT Nuts/lb % Oil Control 46 a 71 a

  • P. Mildew

50 b 72 a Shuck Decline 52 b 70 a

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Pawnee

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‘Pawnee’ Pecan

TRT Length Width Control 47.22 a 23.90 a

  • P. Mildew

45.44 a 23.43 a Shuck Decline 46.15 a 23.60 a

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L S U A g C e n t e r

‘Pawnee’ Pecan

TRT Nut Kernel Percent Weight Weight Kernel Control 9.29 a 5.50 a 59.29 a

  • P. Mildew

8.76 a 5.32 a 60.84 a Shuck Dieback 9.03 a 5.40 a 59.74 a

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L S U A g C e n t e r

‘Pawnee’ Pecan

TRT Nuts/lb % Oil Control 49 a 74 a

  • P. Mildew

52 a 74 a Shuck Decline 50 a 74 a

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PECAN CULTIVAR SUSCEPTIBILTY

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Powdery Mildew

T

  • lerant

Susceptible Highly Susceptible

  • Caddo
  • Gloria Grande
  • Kiowa
  • Moreland
  • P-Cou 2
  • Sumner
  • Jackson
  • Littlepage
  • Maramec
  • Pawnee
  • Curtis
  • Desirable
  • Forkert
  • Melrose
  • Nacono
  • Oconee
  • Schley
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L S U A g C e n t e r

Powdery Mildew

Many growers regularly spraying for scab are surprised to see powdery mildew development on their nuts. Many of the fungicides that are effective for scab are not effective in controlling powdery mildew.

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Fungicides Labeled

  • Group 30, organotin
  • Group 3, DMI’s
  • Group M, guinidine acetate
  • Group 11, strobilurin
  • Group 1, thiophanate-methyl
  • Group 33, phosphonates
  • Group 6, G3 & G11 Mixtures
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Fungicides Labeled

  • Agri-Tin, Super Tin 4L, Super Tin 80WP
  • Enable, Orbit, Propimax, Bumper
  • Elast 400F
  • Abound, Sovran, Headline
  • T Methyl 70 WSB, Topsin-M
  • Agri-fos, Fosphite, ProPhyte, Rampart
  • Stratego, Quilt
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L S U A g C e n t e r

Fungicides Labeled

  • Agri-Tin, Super Tin 4L, Super Tin 80WP
  • Enable, Orbit, Propimax, Bumper
  • Elast 400F
  • Abound, Sovran, Headline
  • T Methyl 70 WSB, Topsin-M
  • Agri-fos, Fosphite, ProPhyte, Rampart
  • Stratego, Quilt
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L S U A g C e n t e r

SUMMARY

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Powdery Mildew

  • Desirable Pecan – significantly reduced nut

length, nut weight, kernel weight, nuts/lb, and oil content.

  • Oconee Pecan – significantly reduced nut

diameter, nut weight, kernel weight, and nuts/lb.

  • Pawnee Pecan – severe infection of

powdery mildew had no significant effect

  • n any of the measured quality

parameters.

L S U A g C e n t e r

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Summary

  • Powdery Mildew infection is sporadic in
  • ccurrence and not considered a significant

economic problem, therefore specific fungicide application for powdery mildew control is not recommended.

  • Fungicide choice for pecan scab control will

impact powdery mildew infection.

L S U A g C e n t e r

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QUESTIONS??