A few weeks ago I noticed some mold spots on my grape vine leaves. I removed the bad leaves but was obviously too late, or the removal was ineffective. I now notice that my butternut squash leaves are dying too. They are about 20 yards apart. Coincidence? - I don't think so. I would like to use an organic remedy but if I have to go nuclear, I will!. I have attached 2 images of the grape vine leaves and 2 of the butternut squash.,
Both grapes and Cucurbits get Powdery Mildew, and probably some other fungi. Look up Downy Mildew, or find out if there are other fungi in your area.
The best control of any fungus is to get the spray on the plant before the fungus spores land on the leaf. Then the fungus is killed while it is still exposed, before it goes inside the leaf.
The rest of this is aimed at Powdery Mildew, but control of other fungi will be similar.
You can spray now, hoping to minimize further damage, and perhaps reduce the population that will be trying to overwinter.
The most 'natural' sprays are those that affect the pH of the leaf surface, usually making it more alkaline than the fungus can tolerate. One recipe includes baking soda (bicarbonate of soda). The problem with this is that it lands on the soil and makes the soil more alkaline. If your soil needs this sort of thing, then go for it! But most soil is already alkaline enough, and spraying baking soda more often than perhaps once a year is not good for it. If you are on a peat soil then it is probably OK to use baking soda. If you are on a high calcium soil then do not!
Over the winter I would again spray the grapes so that any spores overwintering in the bark might be killed. Then, in the spring, as the leaves are starting to leaf out spray again.
The natural remedies are not systemic. They do not enter the plant system, so need to be sprayed on often to protect the new growth. There are man made remedies that do have some slight systemic properties, so might be used less often.
Other controls include pruning the plant so there is plenty of air movement through the leaves.
Squash and its relatives are grown as summer annuals, so if you can get them off to a good start, and get the crop pretty close to harvest it won't hurt anything to let the leaves die off from this fungus. Your technique of removing the worst affected leaves is helping to open up the plant and allow more air through as well as removing some of the reproducing bodies of the fungus.
Charlie - didn't you have some unusual summer weather this year? I've had lots of rain and high humidity this year and am suffering with mildew on squash leaves and am losing cucumber leaves one by one. Some of my roses are suffering from black spot as well. Could your problems be due to your weather?
Thank you Diana and Cindy. I have tried the bicarb of soda but that did not seem to work. I have taken my (meagre) crop and will see if the harsh English winter can clear things up. A comment on the English weather: every summer brings unusual weather - this is England after all!
