Handbook for Irrigation of Wine Grapes in South Africa

Figure 6.25

Chapter 6

A

B

FIGURE 6.25. Examples of grapevine leaves showing (A) blisters on the adaxial side and (B) felt galls on the abaxial side caused by erinose mite.

Figure 6.26

TABLE 6.1. Effect of leaf damage ca sed by erinose mite on midday Ψ L

in Cabernet

Sauvignon near Philadelphia. Leaf status Number of leaves

Leaf area (cm 2 )

Infected area (%)

Leaf water potential (MPa)

Unscathed

20

138±19

0

-1.28±0.07

Infected

20

131±21

2.4±2.1

-1.32±0.12

Black vine weevils are another common pest which may cause extensive leaf damage in vineyards (Fig. 6.26). A pilot study, similar to the one mentioned above, was carried out to determine the effect of leaf damage on midday Ψ L in Mourvèdre grapevines. Under the prevailing conditions, leaf damage caused by black vine weevils did not affect grapevine water status (Fig. 6.27). Since erinose mites or black vine weevils do not seem to damage the veins of laminae, it is unlikely to impair water supply to the rest of the leaf. This probably explains why grapevine Ψ L was not affected.

FIGURE 6.26. Example of damage caused by black vine weevil to Mourvèdre leaves.

IRRIGATION OF WINE GRAPES 167