until fruit set is important. After fruit set, little irrigation is required because shoot elongation slows almost to a halt. Too much irrigation contributes to high canopy density, shading, and lower fruit quality.
After veraison, irrigation is required to replace water lost by evapotranspiration, as an aid to fruit ripening. Keep in mind that the feeding zone for a grape vine is the top metre of soil.
Too much water and the vine grows out of control. Too little and the deeper roots die.
Winter is the time to examine the visible problems of last year’s growth. Strong plants can be pruned to leave more buds than weak plants. If you choose a fixed number of buds per plant, you will have the same problems next year that you had last year. Strong plants will probably grow out of control and have to be hedged or topped, while weak plants may barely ripen their fruit. Perhaps flag the weak plants for special attention?
Add an extra drip emitter or spot fertilize them?
If there’s a weak, sandy area that you can define, perhaps it should be composted to increase organic matter? You get the picture. Some plants may have strong distal growth or strong shoots at the head, with stunted shoots in the centre of the cordon or cane. These are good candidates for Pendulum Bow training or perhaps overlap fruiting canes so that adjacent plants have vigorous distal growth near the weak central growth of the neighbouring plant.
You can thin unwanted shoots in June to bring the growth into balance of about 12 to 15 shoots per metre of VSP row length, regardless of planting density.
Other trellis styles can carry a different shoot density. Yield isn’t only affected by the number of clusters. The weight of individual clusters may be doubled when you compare clusters from primary or secondary buds. Anything that affected bud development or survival can contribute to this year’s low cluster size.
Were the renewal zones of your vines shaded?
Did mildew get out of control? Was it a cold, wet spring when the
28 British Columbia FRUIT GROWER • Summer 2015
first buds were forming?
Spur pruning retains the first buds formed in spring, and the clusters may not be as consistently formed as clusters formed later in warmer, drier weather. Attention to the factors affecting fruit development can have a dramatic impact on yield without significantly increasing your cost of production.
It’s hard to accept that the number of plants per acre is less important than the amount of foliage that covers the vineyard. If you were building a solar collector, would it
matter whether the networked PV units were each one square-metre or two square-metres? Would you hope to capture more energy if the PV units were overlapped? Keep your canopy open and
minimize the number of leaf layers. Expose the leaves to sun and the buds which form in their axils will be fully developed for next year’s crop. The bonus is that UV exposure is lethal to mildew spores and the canopy dries out more rapidly after heavy dew or rainfall. Work smarter, not harder.
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