Not so pretty grapes
We planted ornamental grapes over a black wooden pergola in a sheltered sunny spot about three years ago and they grew well until this year when the leaves became very scraggly and around late February they started shedding early. My mother has them in the South Island and they do really well there, but I’m disappointed in ours. Any ideas? B Dunn, Waikato
It’s hard to tell for sure from your photos but I suspect the cause is one of the fungal diseases that grapes are prone to in warm, humid environments ‒ powdery mildew and downy mildew. And, from personal observation over the years, I get the impression some ornamental grape varieties are quite susceptible to these diseases, particularly to powdery mildew. In areas with drier summer conditions, such as Central Otago, these diseases are much less of a problem on grapes, while the closer you get to auckland and the north the more prevalent they become, in some years worse than others depending on the weather.
What can do you? In autumn, rake up fallen leaves from the vines and burn or bury them, and do the same with any prunings. There are several products you could choose from which could help. Yates Nature’s Way Fungus Spray contains both copper and sulphur which have broad spectrum fungicidal properties and are safe to use, even on edibles. Kiwicare Plant Health Spectrum contains a different type of fungicide as well as an insecticide. Both these should help control mildews. Always follow the label recommendations. Ideally, examine new growth on the vines early in the season and apply spray as soon as symptoms appear, before disease gets established.
If you don’t like the idea of spraying the good news is your vines will probably survive okay, some years they’ll be fine while in others the weather will favour the diseases rather than the vines. There is a plethora of information and homemade recipes online with ideas about how to control powdery mildew and other diseases using baking soda, milk and other ingredients, but most require such diligence in regular applications that they’re often impractical, while others may not be particularly effective. It may be worth considering replacing your grapes with a climber more suited to your environment. A visit to Hamilton Gardens could be worthwhile, to check out which climbers do well there.