Vines have a really useful system SHUT DOWN mechanism. If physiology-cell-tissue variables Red-Line then the chemical signals in the leaves, shoots, and grapes start to move. Chemicals like mammal hormones move though much slower and the message is to SHUT DOWN. If the season is too tough then they will just shut down for the season, it just sends messages to the leaves that OK that’s enough for this year we are shutting up the shop, we will try again next year.
So it drops its leaves the carbohydrates seep away from the shoots and leaves into the cordons, trunk, and deep into the roots, especially the roots, it harbors its photosynthate goodies and then waits, it sleeps bears out he winter in suspended animation. It gathers its goodies into its trunk and mainly its roots and hibernates until next season in which it will try its luck again, the next season bears the hope of a season that could be more conducive to growth and grape berry formation, perhaps a luckier fruit set period, perhaps better rain, hope springs eternal for the possibilities of next season.
Extreme Vine Stress and the tripping of this automatic shutdown sequence.
During the season it is the leaves that give us the best indication of grapevine stress: the leaves are not as green as usual, they may be curling on the edges, there could be holes in them and some leaves have died and have already fallen to the ground. Catch the grapevine stress early to prevent a system-wide vine shutdown.
So the leaves give us the best and easiest visual indication of grapevine stress. When you see evidence of grapevine stress it gives us some time to take some corrective action be it the need for more water(irrigation), the soil may be waterlogged, the nitrogen levels in the vine could be low or some pest is draining the life force from the grapevine trunk. Either way, unhappy leaves mean it’s time to do some doctoring deduction on the grapevine.
Failure to take the right corrective action triggers the vine shut down sequence so that the leaves drop and any bunches of grapes also drop to the ground and your season of grapes is over a lot of investment for the year be it in dollars or time has been lost.
Heat-Related Grape Vine Shutdowns.
Something to bear in mind is the effect of heat on vine shutdown. The vines are growing in spring and summer. In spring the problem will be cold, if the temperature goes below 10 degrees Celsius (50 degrees Fahrenheit) the leaves stop functioning at the top end over 32 degrees Celsius (90 degrees Fahrenheit) the vines also stop functioning. So the photosynthesis stops and the grapevine is under stress. Too many of the heat stress days in a row can force the vine into a full shutdown. The leaf photosynthesis machinery starts up again when the temperature gets back into the right growing range.
Best, Planned Annual Vine Shutdowns.
Do not ignore the vine after you have taken the grapes. You need to invest in next season. The leaves still need to function for as long as possible so that the carbohydrates translocate into the roots. Keep up the water so that it invests as much as possible for next season. These reserves are the starter-motor for next season’s first growth it creates the vegetative burst prior to the shoots becoming net providers of photosynthate goodness.
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