Evaluation of Fungicides for the Control of DampingOff of Tobacco Caused By Rhizoctonia solani

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Evaluation of Fungicides for the Control of
Damping-Off of Tobacco Caused By Rhizoctonia
solani

• R.A. Brammall, A. White and J. DeBruyn
• Canadian Tobacco Research Foundation
• P.O. Box 1, Delhi, Ontario, Canada
• N4B 2W8

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Tobacco Transplant Production in Canada
Tobacco transplants are commonly produced in muck
bed greenhouses Greenhouses using dry or float
Styrofoam cell trays are becoming more common
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Transplant Production Substrates

• Bed culture - Muck mixture of degraded organic
  matter (60-65) with small amount of sand or clay
• Tray culture peat-based mixtures

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All Systems are Susceptible to Damping-Off and
Target Spot Caused By R. solani
R. solani diseases were previously controlled
with benomyl in Canada
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Study Objective

• To identify fungicides and rates suitable for the
  control of Rhizoctonia diseases in tobacco
  transplant production greenhouses
• To assess the effects of treatments on flue-cured
  tobacco quality and yield

R. solani sclerotia in soil
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Test Fungicides

• Thiophanate-methyl (Senator 70WP)
• Trifloxystrobin (Flint 50WG)
• Azoxystrobin (Quadris 250FL)
• Pyraclostrobin (Headline EC)
• Pyraclostrobin Boscalid
• (Pristine WG)
• Boscalid (Endura 70WG)
• Famoxadone Cymoxanil
• (Tanos WG)
• Copper sulfate (Phyton 27)
• Copper hydroxide (Kocide DF)

Candidates selected by potential for registration
in Canada
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Fungicide Studies 2002

• Contrast effectiveness of thiophanate-methyl,
  pyraclostrobin, trifloxystrobin and azoxystrobin
  with benomyl for controlling disease at varied
  rates and effects on yield and quality

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Bioassay Procedure

• Trays seeded with 10 mg seed/200 cm2 and covered
• Day 7 - inoculate with R. solani-colonized rice
  grain for 24 h remove inoculum
• Treat with fungicides after additional 7 days
  (5ml spray volume/200 cm2)
• Measure area affected by Damping-Off after 7-14
  days

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Inoculation Procedure

• Three-week-old colonized rice grain
• Incubated under high humidity on media surface
  for 24 h
• Rice grain removed to leave a foraging mycelium
  of R. solani on and in media
• Produces a more natural inoculum potential

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Thiophanate-methyl (Senator 70WP) in Canada

• Efficacious at rates of 90-125 g product/100 m2
• Emergency Minor Use Registration by PMRA in 2004
  for tobacco
• Active ingredient currently under review
• Replacements may be required

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Fungicide Studies 2003

• Bioassay and field studies
• Strobilurin fungicides, boscalid, famoxadone
  (QoI) and copper compounds

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Efficacious compounds

• Azoxystrobin (? 4 ml product/100 m2)
• Trifloxystrobin (? 11.2 g product/100 m2)
• Pyraclostrobin (? 40 ml product/100 m2)
• Pyraclostrobin Boscalid (? 3.75 g product/100
  m2)
• Boscalid (? 5.31 g product/100 m2)
• Based on Dunnett One-Sided Test with no
  treatment or benomyl as controls.

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Non-Efficacious compounds

• Famoxadone Cymoxanil ( 54 g product/100 m2)
• Copper hydroxide ( 360 g product/100 m2)
• Copper sulfate pentahydrate ( 566 g product/100
  m2)
• Phyton 27 ( 250 ml product/100 m2)
• Based on Dunnett One-Sided Test with no
  treatment or benomyl as controls.

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Field Trial Procedures

• RCB, 4 replications/year standard cultural
  practices
• Fungicides applied twice in greenhouse (true leaf
  1 cm in diameter)
• Harvested plots 2 rows x 23.2 m long with 1.07
  m between rows/replicate
• Hand harvest 6 times/season and flue-cured as per
  normal practice
• Grade price based on 1998 minimum, the Ontario
  Flue-Cured Tobacco Growers Marketing Board

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Effect of treatments on yield and grade and
return indices, 2002/2003
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Effect of treatments on total alkaloids, reducing
sugars and their ratio, 2002/2003
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Strobilurins Induce Precocious Flowering in 2003
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Effect of greenhouse Damping-Off treatments on
plant growth and flower development in the field,
2003
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Conclusions

• Thiophanate-methyl was similar to benomyl for the
  control of Rhizoctonia Damping-Off
• Strobilurins varied in effectiveness
  Azoxystrobin and Pyraclostrobin Boscalid were
  the most effective strobilurin treatments
• Strobilurins caused growth regulatory effects in
  2003 season but not 2002

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Conclusions

• Famoxadone Cymoxanil, Copper sulfate and Copper
  hydroxide were ineffective at the tested rates
• The anilid fungicide, Boscalid, may be useful as
  a resistance management tool for the strobilurin
  fungicides

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