Winetech Technical Yearbook 2022

NOVEMBER

The bud (erinose) mite – identity crisis DEBATES ABOUT WHICH MITES ARE RESPONSIBLE FOR SYMPTOMS LIKE MALFORMED SHOOTS, LEAVES AND BUNCHES, DEAD BUDS, LEAF GALLS AND CURLED LEAF EDGES IN GRAPEVINES HAVE BEEN GOING ON FOR DECADES. COLOMERUS VITIS WAS THOUGHT TO BE A SINGLE SPECIES WITH THREE BIOLOGICAL RACES (BUD MITE, LEAF BLISTER MITE AND LEAF CURL MITE) CAUSING THE DIFFERENT SYMPTOMS.

A

BY ELLEUNORAH ALLSOPP, DAVINA SACCAGGI & BARBARA VAN ASCH

TREATMENT FOR BUD MITE DAMAGE • Spray applications only target the mites while they migrate from dormant to new buds. Contact miticides do not reach mites inside the buds. • At least two sprays per season are required, because the mites do not migrate to the new buds all at the same time. Pay attention to the label instructions about the correct timing of sprays.

AIM Research, funded by Winetech and Stellenbosch University, aimed to determine whether it is possible to distinguish between the mites causing the different types of symptoms when analysing dormant buds. METHOD Mites were extracted from dormant buds, summer buds and leaf galls. Traditional morphological methods, namely light microscope slides and scanning electron microscope (SEM) imaging, were used for

visual descriptions of the mites from the various tissues. DNA was extracted from mites obtained from the different tissues. These genome sequences were compared with each other and with sequences available on the GenBank database to distinguish between genetic groups or species. RESULTS The genetic and morphological analyses showed Colomerus vitis is a species complex consisting of at least five species worldwide which can be distinguished genetically, but not morphologically. Three of these species occur in South Africa. They often occur together in the same bud or leaf gall, and it is not possible to associate any one species with a specific symptom. WHAT DOES THIS MEAN FOR BUD MITE CONTROL? • All three species of Colomerus mites overwinter in dormant buds. Bud mite symptoms develop when mite feeding damages the bunch and leaf primordia in the dormant buds. During the growing season, the mites migrate to the new buds that develop on the shoots or to the leaves, where their feeding results in the formation of leaf galls or leaf curl. • Microscopic analysis of dormant buds remains the only method to confirm the presence of bud mite, since various other factors can also cause malformation of shoots, leaves and bunches, as well as infertile buds. • Bud analyses cannot determine whether the overwintering mites in the dormant buds will cause bud mite, leaf gall or leaf curl damage. • Bud analysis, together with the type of symptoms that occurred in the vineyard during the previous season(s) will determine whether control measures will be aimed at preventing bud mite and/or leaf gall damage.

A

B

Shortened internodes and malformed leaves (A) and malformed bunches (B) due to feeding of mites in dormant buds.

38

WINETECH TECHNICAL YEARBOOK 2022