Insect control vital for South East grape growers

Winegrape growers in South Australia’s South East have been adopting a range of strategies to combat escalating mealybug, scale and sooty mould issues in the region, but they remain a concern, according to local Landmark Viticulture Agronomist Michael Zerk.

Originally from Naracoorte, Michael has been working in the region for five years mainly from the Padthaway area down to Mount Gambier. Prior to this he worked in the Adelaide Hills, Langhorne Creek and Barossa Valley wine regions for three years based from Landmark’s store at Strathalbyn.

He said mealybug and scale populations in vineyards had increased and, of course, were more pronounced in times outside the window of application for insecticide treatments.

Varying conditions in recent seasons have also presented challenges for insect control.

“In previous years, like in 2015, it has been warmer in spring, insects have moved out earlier and we couldn’t get two insecticide applications on. Last season it was cold and wet, growers were favouring fungicide applications and it was not as good for scale early. Then later, it became outside the window of application,’’ Michael said.

“Once the weather warmed up last year, we were coming into early December. Even the beneficial insects were coming out later.’’

He said scale had “smashed’’ some vineyards and there was also increased incidence of mealybugs getting inside grape bunches and causing havoc.

“The other problems with mealybugs and scale are that they exude honeydew, resulting in sooty mould, and these insects are also important vectors for spreading viruses.’’

“Yield potential can be affected and less canopy means heightened risk of sunburn, and flavour can be affected.

“With the sooty mould, you can get downgrading of quality.

“If I was a grower liaison officer (with a wine company), I would be noting it – it is a concern.’’

Michael said many vineyards in the region had been established for around 20 years and he noticed the insects and other problems were increasing with vine age.

“Some growers are not paying attention to how damaging they are. As populations build up, they are also sucking more and more nutrients out of plants and causing bad virus loads.’’

“With some insecticides, we are also knocking around beneficials, like lacewing that will try and get to the scale, and so scale numbers are getting to a point where the population explodes.’’

He said growers had previously tried using winter oil, although it cannot be used after budburst and there were issues around using high rates for optimum coverage.

Chlorpyrifos has been used prior to budburst and has been highly effective, but some companies prefer that it no longer be used in vineyards. A post-harvest application can be effective, or an early knockdown prior to budburst followed by “softer’’ insect control.

Movento, from Bayer, has only been available for use in winegrapes in recent seasons for control of mealybugs and suppression of scale and thrips. 

After leaf uptake, most systemic insecticides are mainly translocated in plants’ xylem along with water and nutrients and are transported upwards. Movento is translocated in plants’ phloem as well as xylem, resulting in transportation upwards and downwards to plant parts not contacted by the insecticide. Movento can better control sucking pests hiding on covered inner leaves than other insecticides, as well as populations that may have developed resistance to existing registered products.

It is also highly compatible with other products and with Integrated Pest Management (IPM) production systems, being ‘soft’ on most beneficial species when used as directed, including parasitoids, syrphid flies, lacewings, predatory midges, ladybird beetles, predatory bugs and earwigs.

“We initially started using Movento for mealybug control, with the idea that it would hopefully suppress scale, and we think it has been doing a good job on scale.

“Mealybug have been in big numbers and we have been happy with the effect on them.

“Even though we had a difficult last season, Movento was still good on mealybug – and for scale we just need the right season. It was a harsh season to judge this year – even picking was four weeks later than usual.’’
  
He said Movento applications had worked well in vineyards and because it had to be applied alone in some larger vineyards, careful planning was required so it could fit in with other applications, particularly fungicides.

“In vineyards with a maintenance program, it works really well. With mealybug, it is now the default decision. If we have alternatives, we will rotate, but otherwise we will use Movento.’’

“We may also look at some out-of-season applications and some chlorpyrifos.’’

Michael said he did have confidence in Movento after viewing its effectiveness on a trip with Bayer in 2012 to New Zealand as well as trial work by Landmark, with funding from the GWRDC.Michael said he was hoping to carry out some further field work with the product in the South East.