Hello – I’m located at College and Dufferin and have a well established grape vine in my backyard. I don’t know the variety – the grapes are green, seedless, small and quite sour. We love the vine for the shade it provides on an arbor over our patio. This year the leaves appear to be covered in small brown spots and they looked quite mangled. The spots seem to develop into holes and the leaves then wither. The stems are also covered in brown spots which I don’t remember seeing in previous years. Some of the leaves appear healthy at first but then seem to get the same problems as the others. I’m sending a picture. We love this vine so much I’m hoping we’re not going I lose it. If there is any advice you can offer we would be very appreciative.
The cool wet weather in Toronto this year has provided the perfect environment for the spread of plant fungal diseases. From your description, it would seem likely that your grape vine has been infected with anthracnose, a pathogen that includes several species of fungi that affect a broad range of plants and trees. In particular, your description of the brown spots that later turn into holes, is consistent with the “shot hole” effect that is characteristic of anthracnose, as are the lesions on the stems.
It is unlikely that a single season of an anthracnose infection will kill your vine, but there is a risk that without proper management, the disease may repeat over several years, putting enough stress on the plant to cause it to go into permanent decline. Left untreated this year, the anthracnose will likely continue to cause cosmetic damage to the leaves and stems, as well as the fruit later in the season. Although Ontario’s pesticide bans limits treatment options, there are likely some allowed foliar fungicides that may be effective. As well, you may want to consider a dormant application of a fungicide next spring before the leaf buds begin to swell as a preventative measure. Ask a reputable nursery about what effective options are available to you.
The pathogen overwinters in the cankers on the stems, and in fallen fruit and leaves left on the ground. In the spring, spores are produced, and are spread by rain. For this reason, it is important to cut out infected canes, and clean up fallen leaves and fruit in the fall. If you have any close neighbours with grape vines, you should encourage them to do the same, as the spores can spread up to seven metres from their source.
The Ontario Ministry of Agriculture, Food and Rural Affairs has produced this information bulletin on the biology and control of anthracnose in grapes that you may find useful.