A Guide to Grapevine Abnormalities in South Africa - P.G. GOUSSARD

GRAPEVINE PESTS Erinose and bud mite 5.4

Erinose After overwintering in buds and egg-laying during bud swelling, hatched adult mites migrate to emerging leaves so as to exercise their feeding activities underneath these leaves. As a result, characteristic indentations (hollows) are created, with protrusions (galls) on the upper sides of the leaves (Photo 324). Young, individual galls are usually richly endowed with masses of white hairy growths on the bottom sides – which turn brown in due course when the galls become older (Photos 325 & 326). In general the galls are not a cause of concern, especially when they occur in limited numbers on a few leaves only on affected grapevines. On the other hand, instances where grapevines are already subjected to severe erinose infestation early in the growing season (Photo 327) – especially where leaves are affected to such an extent that: (i) white growths are noticeable even on the upper sides and (ii) bottom sides are completely covered and the impression is created that massive galls protrude across total leaf surfaces (with edges curling downwards) – should be seen in a serious light (Photos 328 - 330). Based on the fact that the normal physiological functions of leaves may be seriously impaired by erinose (Photo 331) – causing a weaker performance in affected grapevines in the vineyard – it makes sense to emphasise the economic importance of this pest phenomenon. Bud mite Unlike erinose, hatched adult bud mites do not migrate to emerging leaves, but penetrate basal buds especially (first four to six) of lengthening green shoots in order to feed, multiply and eventually overwinter inside them again. Such feeding activities – in the course of the growing season these are usually undertaken by escalating mite numbers at increasing depths in the buds – may cause serious damage to shoot primordia on the whole, or even just to specific leaf and flower cluster primordia. Where there is a high degree of infestation, primary buds may even be destroyed, which may result in a lack of bud burst – a situation that is usually followed by delayed or uneven bud burst of secondary and tertiary buds (which are often infertile) (Photos 332 & 333). In instances where primary buds that have been damaged by bud mite are in fact subject to bud burst and growth, characteristic, visually detectable abnormalities are caused in shoots and applicable organs, namely: (i) smaller, misshapen leaves with rounded tooth edges at the base and overlapping petiole sinus parts; (ii) stunted, blunt and compact bunches and (iii) flat shoots with shortened internodia and a zig-zag growth pattern (Photos 334 & 335). Based on the fact that bud mite may severely hamper normal physiological functions of basal leaves in particular, inducing smaller or even no crop yields – here too (as in the case of erinose) it is deemed justified that the economic importance of this pest be taken into account.

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