Tomato Powdery Mildew

Introduction

Powdery mildew is a common fungal disease that impacts many plants. It is caused by mainly by Oidium neolycopersici and Leveillula taurica on tomatoes. These are obligate pathogens meaning they need living tissue to grow and develop. It is most prevalent on the leaves which can limit yields due to the negative impact on photosynthesis. When conditions are warm and dry (lack of rain) with moderate to high humidity, growers are most likely to see this disease on their plants. Initial onset can also be encouraged by fruit set stress on the plant and unlike what many people think, this disease does not require leaf wetness to cause infection.

Note: The species of powdery mildew that infect other plants like lilac may look similar macroscopically but are a different species, so there is no need to worry about cross infection.

Symptoms

Early on there will be pale yellow, irregular blotches or spots on upper and/or under leaf surfaces, often starting on lower leaves. These will quickly progress to a white or faint gray powdery fuzz that is the spores and conidia of powdery mildew. The fuzz will start as isolated spots on the leaves that will not be limited by leaf veins. These isolated regions will expand to form larger colonies on the outer portion of the leaf.

Host Crops: Solanaceae family (Tomatoes, Peppers, Eggplant)

Identification of Disease

Powdery mildew thrives in warm, dry weather with moderate to high humidity levels but can be suppressed with rain. Optimum temperatures are 60–81°F (15–27°C) with infection occurring below 86°F (30°C). Higher temperatures may slow the disease spread and leaf death. Unlike many other foliar diseases, powdery mildew does not require leaf wetness. It spreads via windblown spores commonly prevalent in the late summer and early fall when temperatures are going through large fluctuations. Coastal areas that have fog, as well as high tunnels, can both be areas of increased disease pressure.

References

Blogs.cornell.edu. (n.d.). Powdery mildew on tomatoes. Cornell University. https://blogs.cornell.edu/livegpath/gallery/tomato/powdery-mildew-on-tomatoes/

Extension.oregonstate.edu. (n.d.). Managing powdery mildew on greenhouse tomato in western Oregon (EM 9413). Oregon State University Extension Service. https://extension.oregonstate.edu/catalog/pub/em-9413-managing-powdery-mildew-greenhouse-tomato-western-oregon

Lucidcentral.org. (n.d.). Tomato powdery mildew. Lucidcentral. https://apps.lucidcentral.org/pppw_v10/text/web_full/entities/tomato_powdery_mildew_314.htm

Pnwhandbooks.org. (n.d.). Tomato (Solanum lycopersicum) - powdery mildew. Pacific Northwest Pest Management Handbooks. https://pnwhandbooks.org/plantdisease/host-disease/tomato-solanum-lycopersicum-powdery-mildew

Purdue University. (n.d.). Tomato diseases. Agricultural Economics, Purdue University. https://ag.purdue.edu/department/arge/swpap/tomato-diseases.html

Ucanr.edu. (n.d.). Powdery mildew on greenhouse and coastal tomatoes. University of California Agriculture and Natural Resources. https://ipm.ucanr.edu/agriculture/tomato/powdery-mildew-on-greenhouse-and-coastal-tomatoes/#gsc.tab=0

Consult and follow pesticide labels for registered uses. To avoid potential phytotoxicity problems, spot test before widespread use. No discrimination is intended for any products not listed.

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Tomato Powdery Mildew

Introduction

Symptoms

Identification of Disease

Prevention

Variety Selection

Cultural

References