Photo caption: Zig-zag shoot growth caused by bud mites.
“Dynamite comes in small packages” is a relevant term when it comes to Colomerus vitis, as these mites are considered a devastating pest in grapevines. Talana Claassen, marketing advisor at VillaCrop provide useful advice on controlling grapevine bud mites in your vineyard.
The wormlike adult mites range from 0.14-0.20 mm in size and have the ability to reduce yield if left untreated. Colomerus vitis consist of three strains that cause a different type of damage, based on their feeding activity.
The three strains include:
1) Bud mite that feeds on and damages young buds.
2) Leaf blister mite that feeds on the leaves, causing galls.
3) Leaf curl mite that causes deformed leaves that curl.
The largest economic impact is caused by the bud mite strain, as damage to the young buds caused by feeding and toxins released during feeding, results in a decrease in grapevine fertility the following season. A high infestation of bud mites could result in the die-off of the primary bud, leaving only the secondary and tertiary buds to potentially burst, but these buds are infertile in most cultivars.
During spring bud mites are carried upwards by growing shoots, from there they migrate to the closest newly forming buds and penetrate them. Bud mites feed, multiply and overwinter within buds. The buds closest to the base of the shoot usually contains the greatest number of mites, but they can be found higher in the buds higher up on the shoot as well. A bud mite infestation are visible during spring, shortly after budbreak.
Symptoms include delayed and uneven budbreak, flat shoots with shortened internodes in a zig-zag growth formation, as well as smaller, deformed leaves and bunches. To accurately determine the extent of a bud mite infestation, canes should be sent to a laboratory to evaluate the dormant buds for the presence of bud mites under a microscope. Canes samples can be sent in for evaluation after leaf fall ( May) until prior to budbreak occurs.
Guidelines provided by the laboratories state that chemical control is required if the bud mite infestation exceeds 30% of the dormant bud samples sent in for evaluation. Recommended acaricides for the control of bud mites include fenpyroximate and fenazaquin. These acaricides, registered for the control of bud mite, work via a contact action with no systemic properties. An application should therefore be targeted for the time period when migration of the mites occur from dormant buds to newly developed buds.
When shoots have reached 10 cm in length and new buds develop, the first application should be applied, followed by a second application 14 days later. Under Under high infestation a third application might be required, which should be applied prior to any signs of flowering. In cases of a severe bud mite infestation, applications over a few seasons might be required to gradually lower the percentage bud mite infestation. In order to ensure effective coverage of the contact acaricide, a high water volume is recommended.
It is important note that any chemical control measure applied during spring of the current season, will only reduce the bud mite infestation of the following season. Application takes place during the migration of bud mites from the damaged dormant bud, containing the current seasons yield, to the newly developed bud, in which the following seasons potential yield will develop.