Bug Eat Bug

A vineyard, especially at this time of year, is a beautiful sight, green, lush and bursting with life and the promise of grapes to come. As we explained recently, we need to be careful how we manage this natural system, and ideologically-driven methods aren’t necessarily the best. We implement ‘integrated pest management’, in other words, we look carefully at the ecology of the vineyard and the impact that any intervention has on the whole system.

One insect pest that we normally see at low levels in the vineyard, grapevine scale, has become a little more prevalent recently. Recent research undertaken here by a student from ANU suggests that the dry winter may be partly to blame – scale can tolerate frosts much better when its dry than when its wet.

Rather than spraying scale with chemicals that could also harm beneficial insects, we decided to release more beneficials, in this case purchasing ladybeetle larvae and releasing them onto the vines. This appears to have been a great success, the larva rapidly establishing themselves, feeding on immature scale and growing quickly.

However, there was a bit of a surprise as well – normally we don’t have much control of scale by parasitic wasps, but when Dr Paul Cooper, the leader of the ANU research team, came recently to collect some adult scale to infest vines for an experiment, he wasn’t able to find any that hadn’t been parasitised. So in one season we’ve been able to go from higher than normal levels of scale, to having the immature scale consumed by introduced ladybeetles, and the adults killed by parasitic wasps already here.

We’re left wondering if the change that we made to stop spraying elemental sulphur for powdery mildew control has been the factor that has allowed beneficials like the parasitic wasps to thrive just when we needed them. If we were an organic vineyard, we’d still be spraying sulphur and probably still killing the beneficials. Again, we’ll keep watching what happens and assessing everything on its ecological merits: there’s no room for ideology in a healthy vineyard.