Powdery mildew

Causal organism: Fungus

Important species

Powdery mildew of tomato, pepper, eggplant, potato and other solanacoeus crops, squash, cucumber and other cucurbits (Erysiphe orontii)

Powdery mildew of carrot (E. polygoni)

Powdery mildew of cucurbits (E. cichoracearum; Sphaerotheca fuliginea, Podosphaera fusca; P. fuliginea)

Host plants

Cereals, grasses, vegetables, ornamentals, weeds, shrubs, fruit trees, and forest trees

Affected plant stages

Seeding, vegetative, and reproductive stages

Affected plant parts

Leaves, petioles, stems, and sometimes, fruits

Symptoms

Photo courtesy of Andy Wyenandt
The Ohio State University


Powdery mildew is characterized by a dusty-white to gray coating and talcum powder-like growth commonly infecting plant's leaves. It begins as circular, powdery-white spots that turn yellow-brown and finally black. In most cases, the fungal growth can be partially removed by rubbing the leaves.

Powdery mildew is commonly found on the upper side of the leaf. It also infects the underneath surface of the leaf, young stem, bud, flower, and young fruit. The infected leaf becomes distorted, turns yellow with small patches of green, and falls off prematurely. Infected buds fail to open. Other injuries include stunting and distortion of leaves, buds, growing tips, and fruits. Infected seedlings will eventually die.

Conditions that favor development

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1. Warm and dry climate with high humidity
2. Infected seeds and planting materials
3. Overcrowded plants

Prevention and control

1. Plant resistant cultivars when available
2. Practice a wider spacing between the hills and the rows to increase air flow among plants, and light penetration
3. Practice crop rotation
4. Remove infected plant materials and alternative hosts
5. Prune overcrowded plants to increase air circulation, reduce the relative humidity, reduce infection, and increase the light penetration
6. Plow under all plant residues or remove plant residues after harvest. Do not place infected plant materials on the compost pile
7. Ginger powder extract
8. Neem seed extract
9. Papaya extract
10. Turmeric extract
11. Baking soda
12. Bordeaux mix
13. Seed treatment
14. Compost tea

External links

• ICARDA. Field guide to lentil diseases and insect pests: Fungi. http://www.icarda.cgiar.org/Publications/Field_Guides/Lentil/Lent1.Html
• Cornell University. Powdery mildew on cucurbits. http://vegetablemdonline.ppath.cornell.edu/factsheets/Cucurbits_PM.htm
• The Ohio State University. Powdery mildew on summer squash. http://www.ag.ohio-state.edu/~vegnet/problem/pb71801.htm
• UC. Powdery mildew on vegetables. http://www.ipm.ucdavis.edu/PMG/PESTNOTES/pn7406.html

References

• Brooklyn Botanic Garden. (2000): Natural disease control: A common-sense approach to plant first aid. Handbook # 164. Brooklyn Botanic Garden, Inc. 1000 Washington Avenue, Brooklyn, NY.
• CABI. (2004): Crop protection compendium. 2004 Edition. CAB International Publishing. Wallingford, UK.
• Ploetz, R.; et. al. Editors. (1998): Compendium of tropical fruit diseases. APS Press, The American Phytopathological Society. Saint Paul, Minnesota, USA.
• Thurston, D. (1998): Tropical plant diseases. Second Edition. APS Press. The American Phytopathological Society. St. Paul, Minnesota, USA.
• Wagner, Georg. (2004): Vegetables' pests. Personal Communication. Schopperplatz 14, 4082 Aschach / Donau.