Winetech Technical Yearbook 2022

F

C

G

Worm-like Colomerus mites in a dormant bud (F) and on the bunch primordium in the bud (G) are only visible under a microscope.

instructions, because some products should not be applied during flowering. • If leaf galls are first noticed during the growing season, it is important to apply control before too many hairs (trichomes) develop in the galls, as they will reduce mite exposure to the contact miticides. SAMPLING FOR BUD ANALYSIS • Cut shoots before pruning when vines are dormant. • Cut 12 - 16 shoots distributed through the block (1 - 2 ha) – fewer shoots do not provide adequate representation of mite occurrence and distribution in the block (can miss infested spots). • Cut shoots back to the first six buds. • Secure shoots from each block securely – shoots that become detached cannot be assigned to the correct block or sample. • Place in a plastic bag and keep out of the sun so that buds do not desiccate. • Keep samples cool (fridge), but do not freeze. • Mark each bundle of shoots (sample) clearly with the farm name and block number. • All samples must be accompanied by a completed and signed ARC application form for diagnostic services.

D

E

Leaf galls (C & D) and leaf curl (E) caused by mites feeding on the underside of leaves during the growing season. Thick hairs (trichomes) protect the mites and repel pesticide sprays.

• If bud analysis shows infestation of ≥50% in a vineyard, control measures should be applied over at least two to three consecutive seasons to achieve satisfactory control. TREATMENT FOR LEAF GALL DAMAGE • Sulphur suppresses mites and can help to suppress leaf gall and leaf curl damage, but it will not control outbreaks. • In vineyards where severe leaf gall symptoms occurred in the preceding season, the first spray application is done at 10 cm shoot length to target mites when they migrate from the dormant buds to the new leaves. Pay close attention to the label

REFERENCE https://www.wineland.co.za/the-bud-mite-identity-crisis/

For further information, contact Elleunorah Allsopp at 021 809 3007 or allsoppe@arc.agric.za. For bud analyses, contact Muriel Knipe at 021 809 3463 or knipem@arc.agric.za.

39

WINETECH TECHNICAL YEARBOOK 2022