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I have a grapevine on the southwest. It was put in by the previous owners so I don’t know the specific variety. I have not yet managed to harvest from this plant; we moved in a bit over a year ago and for the second year in a row we have plenty of grapes but they burst open before ripening and seem to be completely dry from the inside.

I’ve read that when this happens with tomatoes it can be due to excessive or irregular watering. We had a relatively dry summer so far and I have watered every 1-2 days during dry spells, but not when there was rainfall. When watering I used one watering can (10L) on this plant plus immediate surroundings (some small decorative flowers).

Apart from the problem with the fruits there are some red spots on some leafs, which looks a little like what aphids did earlier in the year to my red berry plants, although I don’t see any animals or eggs on the grapevine and it’s mostly the old foliage that’s affected.

Since moving in I have given the grapevine fertilizer once, this spring. I don’t have details about the soil, except that it’s primarily sand. This is in the Netherlands.

What may be causing the problems with this grapevine and how can I fix it for this or next year?

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  • Could it be a type of grape that is green in color when ripe ? And then split when overripe. Aug 7, 2022 at 16:31
  • @blacksmith37 nice idea, but I sampled one and it definitely wasn’t ripe, very sour.
    – user39350
    Aug 7, 2022 at 17:56
  • Are you having sunny but near freezing cold mornings? Aug 8, 2022 at 7:12
  • @PolypipeWrangler the lowest minimum was 9 degrees Celsius since half June.
    – user39350
    Aug 8, 2022 at 9:00

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This is a guess:

Leaf with red dots:

Grapevine Leafroll Disease virus:

Leaf symptoms first become apparent in early to mid-summer... In most red cultivars, GLD causes reddening of the interveinal areas while the primary and secondary veins remain green.

I think this description comes rather closed to your photo including roll of the leaf.

The burst open grapes:

Because especially the cracked grape in the background seems to be healthy without any fungus like for instance powdery mildew, then I think, as you suspect, it is likely because of irregular watering and rainfall. Often cracking in fruits happens on a wet day after a long dry period.

From Gardening know how:

The exact cause of grapes that are cracking open is still under debate, but all camps seem to agree that it stems from irrigation, either an over abundance or lack thereof. While grapes will adapt to lower water conditions, yields will be reduced. Ideally, irrigation is essential for optimum production and quality of fruit. The timing of this irrigation is of primary importance.

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