Cucumber disease

Asked July 3, 2018, 7:42 AM EDT

My Bush cucumber plants have some white spots with a slight brown edge around them. I don’t see any insects on the plants other than an occasional ant Is this a fungus and how should I treat it? The plant look healthy otherwise and are 14 inches tall. I water well once daily unless it has rained and use a balanced vegetable fertilizer

Livingston County Michigan disease issues cucumbers

1 Response


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I can’t tell for sure from just the picture, but I think that your cucumber plants might have angular leaf spot, caused by a type of bacteria called Pseudomonas syringae pv. lachrymans.

Here are some other resources that can help you determine what type of spots your cucumbers might have:

Diagnostic Key: Disease of Cucurbit Leaves from Cornell University

Cucumber > Leaves > Spots on leaves from University of Minnesota Extension

To better determine whether the spots are from a pathogen, and which one, you can examine the leaves when they are moist, such as from morning dew, and look for “signs” of the pathogen. Can you see “ooze” that would indicate bacterial infection? Can you see any fungal spores or growth?

Now, you said that you water well once daily. Of course, it is good to make sure your plants have sufficient water, but I have a few questions about the watering:

· What time of day do you usually water?

· Are you wetting the leaves?

· Do you check that the soil is getting dry, and that your plants need water every day?

These things are important because plant diseases generally need moisture to survive, infect, and spread. When water sits on the leaves of a plant it provides a better opportunity for bacteria and fungi to infect; usually, the longer the water or water droplets sit on the leaves, the greater the chance of pathogen growth and infection. Thus, it is good to avoid wetting the leaves and water your plants in the morning, if you can, so that the leaves have time to dry out during the day. Only the roots need water! In addition, many fungal and bacterial pathogens can be spread by water splash. It is also good to avoid working with the plants when they are wet. These are all best practices; certainly, it’s better to water your plants at night than for them to die of drought. :-P

New transplants do generally need to be watered daily, and we have had some hot weather! But it still doesn’t hurt to stick you finger in the soil near the plants and see if it has dried out or not. Perhaps you could water deeply every other day. But do check the moisture level! You can also refer to this article on “Smart watering in the vegetable garden.”

I would start with thinking about your watering practices, as mentioned above. In taking an integrated approach to plant disease management, you start by thinking about your “cultural” practices, like watering, plant spacing, etc., and, if necessary, chemical control methods can also be considered.

Copper-based products can be considered to protect the cucumber plants from further infection and disease spread. Although, these products are not going to cure what is already diseased. When copper is used as the active ingredient in a pesticide product, it can have protectant properties against both fungi and bacteria. Here is a chart from the University of Delaware of some fungicides and bactericides that may be available for home use: Fungicides and Bactericides Available for Home Use 2015. Be sure to carefully read and follow all product label instructions. Also, be sure that the product is labeled for use on the specific host plant (i.e. cucumber or vegetables). Products with different active ingredients may be more effective against different types of pathogens.

Next year, you can also consider looking for plant varieties that are more resistant to diseases like angular leaf spot or powdery mildew.

Hope this helps! Let me know if you have further questions.



Resources compiled:

Cucurbits, Leaf Spots from UMass Extension

Diagnostic Key: Disease of Cucurbit Leaves from Cornell University

Cucumber > Leaves > Spots on leaves from University of Minnesota Extension

Smart watering in the vegetable garden from Michigan State University (MSU) Extension

IPM: Smart pest management for the vegetable garden from MSU Extension

Fungicides and Bactericides Available for Home Use 2015 from Delaware Cooperative Extension

Tables of disease resistant varieties from Cornell University