Grape vines grown under glass can suffer from shanking, which means that individual berries within a bunch do not colour up properly, and eventually shrivel up. The affected grapes are inedible.
Plants affected: Grape vines grown indoors
Main causes: Cultural
Timing: Late summer
Shanking occurs when within a bunch of grapes, individual berries fail to develop their colour. Black grapes remain red and white grapes remain translucent. Affected grapes persist on the bunch, becoming wrinkled and eventually resemble raisins. The flavour of these grapes is unpleasantly sour and watery.
This problem generally results from a variety of growing problems. These include:
- A poor root system, usually due to waterlogging
- Soil compaction
- Poor nutrition
- Excessive pruning when in leaf
- Pest and diseases
- Spring chilling in unheated greenhouses
Some simple measures can help prevent shanking:
- Avoid cropping young vines in the first two years after planting, and allow only three or four bunches in the third year
- Do not exceed more than one bunch per branch on established vines
- Pinch out new shoots regularly during the growing season, following the relevant pruning and training methods
- Cut out the affected berries
- Ensure that the vine has adequate but not excessive watering or feeding to its root area
- Give a foliar spray feed as an instant boost
- Ensure there is adequate drainage
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