Whitish spots and yellow spots - Ask Extension
What is causing these whitish and yellow spots on my cucumber leaves?
Knowledgebase
Whitish spots and yellow spots #799507
Asked July 05, 2022, 2:32 PM EDT
What is causing these whitish and yellow spots on my cucumber leaves?
Baltimore City County Maryland
Expert Response
Hi-
There are several cucurbit diseases that start off with this indistinct yellow/tan spotting: anthracnose, target leaf spot, angular leaf spot, cucumber downy mildew (active in states around us and is likely in MD).
This appears to be anthracnose. If it is, the dried lesion centers will drop out leaving holes in leaves. Cucurbit diseases
all tend to slowly and steadily send plants into a death spiral (quicker in hot, wet weather of course). Infections that occur prior to flowering/fruiting often greatly limit fruit production.
You can try protecting them with a copper-based fungicide, though that will not cure the existing infection and is most effective when applied as soon as symptoms are observed.
Verify the product label includes vegetables as safe for spraying, and follow its instructions about how to apply, when to re-apply, and how long to stop applying prior to harvest. Avoid making applications during temperatures above 85 degrees. Since the plants are relatively young, removing badly infected leaves may deprive the plant of foliage needed to produce flowers and fruits to continue producing. Be sure not to leave any plant parts in the garden whenever you decide to remove the plants.
You can plant a second crop within the next 2 weeks. Consult this Cornell University web page listing disease-resistant varieties.
Additional information:
There are several cucurbit diseases that start off with this indistinct yellow/tan spotting: anthracnose, target leaf spot, angular leaf spot, cucumber downy mildew (active in states around us and is likely in MD).
This appears to be anthracnose. If it is, the dried lesion centers will drop out leaving holes in leaves. Cucurbit diseases
all tend to slowly and steadily send plants into a death spiral (quicker in hot, wet weather of course). Infections that occur prior to flowering/fruiting often greatly limit fruit production.
You can try protecting them with a copper-based fungicide, though that will not cure the existing infection and is most effective when applied as soon as symptoms are observed.
Verify the product label includes vegetables as safe for spraying, and follow its instructions about how to apply, when to re-apply, and how long to stop applying prior to harvest. Avoid making applications during temperatures above 85 degrees. Since the plants are relatively young, removing badly infected leaves may deprive the plant of foliage needed to produce flowers and fruits to continue producing. Be sure not to leave any plant parts in the garden whenever you decide to remove the plants.
You can plant a second crop within the next 2 weeks. Consult this Cornell University web page listing disease-resistant varieties.
Additional information:
https://ag.umass.edu/vegetable/fact-sheets/cucurbits-anthracnose
https://extension.umn.edu/diseases/anthracnose-cucurbits
https://plantpath.ifas.ufl.edu/u-scout/cucurbit/target-spot.html
https://content.ces.ncsu.edu/cucurbit-downy-mildew
https://ag.umass.edu/vegetable/fact-sheets/cucurbits-leaf-spotshttps://extension.umd.edu/resource/cucumbers
Thank you for this information. I thought Marketmore cucumbers were supposed to be resistant to this disease. I guess it is not totally immune. Tiny white spots seem to be on the leaves of almost everything in the garden in the front yard and backyard, including flowers, vegetables, foliage plants. It does not look like powdery mildew. Is this a virus? (See attached)
Thanks.
Terry
Hi-
I am a big fan of Marketmore cucumber. Yes, the degree of disease resistance can vary between varieties listed as having resistance to a particular disease. No cucumber varieties are 100% immune. When conditions are especially favorable- warm, wet weather and lots of inoculum- infection of resistant varieties is more likely.
The white spots on the bean leaves is most likely from leafhopper feeding. If you brush the plants you will see them fly up. Tiny white dots (stipples) on plant leaves are usually a symptom of feeding by some type of sucking insect pest- thrips, leafhoppers, planthoppers, bugs, whitefly, aphids, spider mites, etc. Examine leaf undersides with a hand lens to try to find and identify the pest(s).
Jon
I am a big fan of Marketmore cucumber. Yes, the degree of disease resistance can vary between varieties listed as having resistance to a particular disease. No cucumber varieties are 100% immune. When conditions are especially favorable- warm, wet weather and lots of inoculum- infection of resistant varieties is more likely.
The white spots on the bean leaves is most likely from leafhopper feeding. If you brush the plants you will see them fly up. Tiny white dots (stipples) on plant leaves are usually a symptom of feeding by some type of sucking insect pest- thrips, leafhoppers, planthoppers, bugs, whitefly, aphids, spider mites, etc. Examine leaf undersides with a hand lens to try to find and identify the pest(s).
Jon
