Grapevine disease Downy Mildew (Plasmopara vitikola) is a fungal disease that affects a grape leaves. (Getty Images)
Q. It happened again! I wrote last year about a white coating on my grapes which you diagnosed as fungus. Lost all the grapes. This year there are many bunches of grapes, all covered with the same white coating. I sprayed with copper but to no avail. The leaves and vines are involved with spots on the vines and rust-colored spots on the leaves. Any hope for the vine or should it be removed?
I’m sorry to hear that your grape troubles are still with you.
Powdery mildew is very common in grapes, especially in our Mediterranean climate. The spores will spread during rainy weather (which we’ve had a lot of this year), then establish when the temperatures rise. Powdery mildew, unlike most other fungal diseases, doesn’t need moist conditions to grow. It favors shade and mild temperatures, so if your grapes are not getting full sun that could increase the likelihood of powdery mildew.
If the infection is caught early, prune out the affected branches and spray every ten days until daytime temperatures reach 90. Sulfur, neem oil, horticultural oil, jojoba oil, and Serenade are all approved treatments for powdery mildew.
Since you report rust-colored spots on the leaves and fruit loss, I suspect your grapes may be infected with another, additional, disease. Measles (in grapes this is a fungal disease), Pierce’s disease, or (less likely) Phomopsis.
The likelihood of saving your grapevines depends on the extent of damage and your ability to improve the growing conditions. First, remove any affected branches and dispose of them in the trash. If all the branches are affected, you’ll probably just want to remove the whole plant. Is the vine getting full sun? Is it in a location that allows for good air circulation? Will you remember to spray it every 10 days? I would recommend starting over with a new grapevine in a new location.
Q. We have had one passion fruit vine for about 4 years that has never borne flowers. The vine grows long branches every year and we live in the Corona area. We have had other passion fruit vines that bore flowers and produced fruit.
Can you tell us why this vine doesn’t produce flowers?
If the vine is otherwise healthy (and yours seems to be), the plant may not be old enough to produce flowers. Most of our fruit-bearing plants haven’t produced fruit before they were 4 or 5 years old. It might just be taking its time.
Passion vines are not fussy about soil or growing conditions, but they do need full sun to flower. Give it a fence or trellis to climb so it can get more sun exposure.
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