Handbook for Irrigation of Wine Grapes in South Africa

Chapter 7

A useful guideline for irrigation of young grapevines is the qualitative, visual assessment of the shoot tips. Since there are usually no bunches on newly planted grapevines, shoot elongation will continue for a longer period, compared to mature, full-bearing grapevines. As long as the young grapevines experience no water constraints, shoot elongation will continue. The growth tips will appear to be “ahead” of the older, more matured leaves (Fig. 7.5A & B). If soil water becomes limited, shoot elongation will slow down, but the older leaves will continue to enlarge. At this stage, the older leaves seem to cover the growth tip (Fig. 7.5C). This symptom is often referred to as the “Christmas tree” effect, and serves as an indication that irrigation should be applied. At this stage the shoot tip should still be active, i.e. light green (Fig. 7.5C). When following this approach, it must be remembered that the young grapevines are not bearing any crop that could be damaged. Figure 7.5

A

B

C

FIGURE 7.5. Grapevine shoot tips indicating (A) no water constraints, (B) little water constraints and (C) the onset of water constraints.

Figure 7.6 Flat plastic caps or “Mexican hats” are sometimes fitted onto micro-sprinklers to restrict the wetting pattern (Fig. 7.6). Consequently, only a fraction of the available soil volume will be wetted, e.g. as in the case of drip irrigation. If this practice is applied in newly planted vineyards, root development will be limited to the wetted soil volume. The caps are usually removed in the second or third year to increase the wetted soil volume. At that stage, root development might not extend concomitantly due to natural re-compaction of the soil after deep preparation as discussed above. In many vineyards, inevitable wheel track compaction will cause an additional restriction to lateral root development into the work row.

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