Microdochim Blight of Pumpkin White Speck

1
Microdochim Blight of Pumpkin(White Speck)

• L. H. Rhodes, R. M. Riedel,
• G. Sutton, L. Wutz, and R. Precheur
• The Ohio State University, Columbus

2
Microdochium Blight of Pumpkin (White Speck)

• A serious fungal disease of pumpkin and gourd.
• Favored by hot humid weather with frequent rains.
• Caused by the fungus Plectosporium tabacinum
  (formerly Microdochium tabacinum)

3
Importance

• Blights foliage of mature plants.
• Kills developing shoots.
• May kill small plants.
• Produces unsightly lesions on fruit.
• Reduces yield.
• Blights

4
Disease Symptoms
5
Diamond-shaped lesions are found on stems,
petioles, and leaf veins.
6
Lesions on fruit are small, irregular specks
7
Individual lesions merge together to form large
area of dead tissue.
8
Heavily infected green fruit.
9
Field Symptoms

• Disease appears suddenly and develops rapidly.
• Uniform development throughout field.
• Uniform development on individual leaves and
  fruit.

10
History of Microdochium Blight (White Speck) in
U. S.

• 1981 Louisiana
• Reported as a new disease of cucurbits
• Given name White Speck
• Pathogen described but unidentified.
• 1988 Tennessee
• 1989 Found in Ohio (Ross Co.)

11
The Pathogen Plectosporium tabacinum

• Also known as Fusarium tabacinum, Microdochium
  tabacinum, Plectosphaerella cucumerina and at
  least 5 other names.
• Parasitizes a wide range of hosts, from tobacco
  to crawfish.
• Found worldwide.
• Considerable isolate variability.

12
The Pathogen Plectosporium tabacinum

• Produces masses of spores in lesions on host
  surface.
• Spores dispersed primarily by splashing water.
• Importance of windborne spores not known.
• Survival most likely in infested crop debris in
  soil.

13
Hosts

• Wheat
• Milkweed
• Violet
• Muskmelon
• Pumpkin
• Many other plants

• Beet
• Tomato
• Potato
• Tobacco
• Celery
• Ginseng

14
Are Weeds Sources of Inoculum in Pumpkin Fields?
15
2003 Weed Survey

• Examined weeds in Clark, Highland, Miami,
  Champaign, Holmes, and Franklin Counties.
• Weeds were growing among pumpkins with obvious
  symptoms of Microdochium Blight.
• Laboratory culturing done on lesions if
  questionable.

16
Weed Species Examined

• Purslane
• Canada thistle
• Giant ragweed
• Velvetleaf

• Lambsquarters
• Redroot pigweed
• E. Black Nightshade
• Dandelion
• Penn. smartweed

17
2003 Weed Survey

• No confirmed infection in any weeds examined.
• Detached leaves in moist chamber were colonized
  by P. tabacinum when artificially inoculated.
• Further experimental inoculations now being done
  in greenhouse.

18
Pathogen Variability
19
Isolate 12-1 Pumpkin
Isolate 12-2 Bur-cucumber
Isolate 12-3 Pumpkin seedling
Isolate 12-4 Gourd debris
Control
Isolates vary in ability to cause disease in
pumpkin.
20
Severity of 4 isolates of Plectosporium tabacinum
on Pumpkin (Greenhouse tests)
21
Severity of 4 isolates of Plectosporium tabacinum
on Pumpkin (Greenhouse tests)
22
Options for Control

• All commercial varieties are susceptible.
• Currently, fungicides are the only option for
  adequate control.

23
Effects of Fungicides on Disease Severity Ratings
for Microdochium Blight of Pumpkin, 7 days after
spraying.
24
Effects of Fungicides on Disease Severity Ratings
for Microdochium Blight of Pumpkin, 14 days after
spraying.
25
Acknowledgments

• Research support provided by
• The Ohio Vegetable and Small Fruit Research and
  Development Program.
• USDA/Ohio Department of Agriculture Block Grant.
• Ohio Agricultural Research and Development
  Center.

26
Acknowledgments

• Special thanks to
• Becky Lyon
• Jennifer Ariss
• Andy Wyenandt
• Harold Brown