Today I noticed powdery mildew (I think) on two different cucumber plants. What should I do?? Some say sulphur but the directions on the box say not for cucumbers. I appreciate your advise. Thanks, Bev
take off the leaves to try to keep it from spreading - keep the plants as dry as possible and hope for low humidity - there are few ways to deal w/ mildew otherwise, and fungicides [especially sulpher] seem to be more prevention that cure - the focus commercially for mildew on tomatoes, cukes and peppers is to use resistent varieties, keep humidity low, use fungicides before it hits
you may also have something else, like downey midew, or another thing altogether
I take powdery mildew as a sign to pull the plant out and replace it with something else. If it happens often in your garden, you might plan to have backup cuke plants next year.
I hear a ten percent milk solution will prevent and treat powdery mildew. That's one part milk to nine parts water sprayed early in the morning or in the evening to prevent burning the plant by wetting it in full sun.
Either/or a teaspoon of baking soda in 1 quart of water, wit a couple of drops ofa light oil (such as corn, cannola, peanut), or a 50/50 mixture of fat free milk and water stops PM in a short time when it appears on my lilacs. No real reason to remove the leaves.
I've been the Cornel Forumla (basically, baking soda as described above, exact recipe at (pdf):
I spray once or twice a week and it has significantly slowed down (not completely stopped) powdery mildew on pumpkins, lemon cucumbers, and watermelon, as well as "rust" and some type of mildew on some old roses.
You've got what? A couple of weeks at most until frost gets these plants? The PM just isn't going to significantly impact your fruit production (which will be declining with cooler temps anyway) in the meantime.
Powdery Mildew is mostly opposite of downy mildew in that it thrives in dry weather, not humidity. Powdery Mildew does not require free water to propogate. The hyphae only burrow into the epidermis layer of the upper side of the leaf. Some home spray remedies work because any spraying (water too) during the day will remove the fungal structures off the leaf surface (it is delicate).
However, increasing daytime free moisture will reduce powdery mildew and quite possibly increase the likely infestation of moisture-loving downy mildew. Downy mildew is much more destructive and attacks through the leaf structure itself. If you have that fuzzy mildew on the underside of the leaf, then you are quite sure to have downy mildew setting up shop there.
Sulfur dust has been the #1 remedy for powdery mildew, however you will want to sample this on a leaf and be careful with this and any fungicide material.
The link to The Cornell University Âfungicide' formula doesn't work, so here it is :
"1 tablespoon each of baking soda and either a light horticultural oil or regular vegetable oil, to 1 gallon of water. If using vegy oil, then add a bit of insecticidal soap. Shake well before and during application. This treatment helps reduce blackspot and mildew"
(taken from here: http://southerncaliforniagardenclub.org/Tips%20&%20Hints.htm )
From my childhood i remember, we used fresh manure (1 part of manure to 10 parts of water) - to spray on leaves. Usually it worked.
I started experimenting last year spraying with tea made from herbs immune to mildew. So far I have had good luck with rosemary tea and Mexican oregano tea.
Spray it with Neem every 3 days & it may clear up. I spray most vegtables with neem & it seems to stop most mildew & insect problems. search the web for more info