Viticulturist and passionate insect watcher Jenny Venus has some sage advice for grapegrowers as they head into spring: 'Follow the ant trial’.
It’s a simple strategy, but one that Jenny says could have significant impact on the overall health of a vineyard.
‘It’s important that growers monitor and check their vineyards for pests and diseases during winter and early spring. This is the time to look for diseases such as phomopsis and insect pests such as mealybug and grapevine scale’, said Jenny, a consultant viticulturist with Brad Case Contracting and Kimbolton Wines.
Jenny said both of these insect pests can cause significant issues throughout the season if they are not monitored early.
‘Mealybug and grapevine scale can spread viruses across vineyards, which can have a significant impact to the overall vineyard health. Even in the short term, these insects secrete honeydew that sooty mould grows on, causing a downgrade in fruit quality.’
Jenny said a handy hint when monitoring for insect pests in spring is to follow the ant trial.
‘Ants feed on the honeydew produced by mealybug and scale and hence are often found in association with the pests. If ants are present on the vines, peeling back the bark on the cordon or spurs will often reveal mealybug nymphs and juvenile grapevine scale.’
– Jenny Venus
If the insect pests are found in the vineyard, Jenny said tagging a few vines that are infested allows for easy monitoring later in the season.
Jenny said it is important for growers to know if mealybug or scale are present in their vineyard – and if they are, to determine the level of infestation.
‘If high numbers are found in spring, a spray prior to flowering or fruit set may be required.’
‘If left uncontrolled and the weather conditions are variable for breeding – that is, mild humid conditions – both scale and mealybug could have a significant impact on fruit quality.’
Ants feed on the honeydew produced by mealybug and scale.
Jenny said while dry, hot summers do not favour outbreaks of scale and mealybug, the conditions within a large canopy that is irrigated ‘are often quite different to the forecast weather conditions.’
‘Even though it may appear that the weather conditions may not favour a mealybug outbreak, the microclimate within the canopy may be conducive to mealybug and scale breeding and the production of honeydew and sooty mould.’
She said it was critical that grapegrowers understood the impact that mealybug and scale could have on their vineyard – and sought advice if they were unsure on how to monitor or what the pest looked like.
To learn more about mealybug management, read Wine Australia’s factsheet here.
How to monitor for mealybug in spring
By late September to November, mealybugs will be at the crawler or young nymph (juvenile) stage. You can check for them on the underside of leaves:
- use a 10x hand lens
- sample leaves in risk areas or areas previously infested
- select leaves near vine crown, and
- record the percentage of infested leaves from, say, a 100-leaf sample, taken as 25 leaf samples from each of 4 double rows within a block.
Source: Mealybug Management fact sheet