Scale & sooty mould posing challenges for grapegrowers

Increased infestations of scale and the related sooty mould have been growing problems for South Australian winegrape growers in recent seasons.

Adelaide Hills viticulturist and grower Kim Anderson says he sees every shoot whilst closely tending his 34,000 vines and any disease or bugs gives him “the cold sweats’’.

Kim and his wife, Michelle, who works for the University of Adelaide, grow a wide range of grapes over 14 hectares at Charleston, including Sauvignon Blanc, Chardonnay, Gruener Veltliner, Pinot Noir, Tempranillo, Graciano, Maturana Tinta and Grenache Gris.

Their grapes are sold predominantly to the locally-based Somerled Wines and Artwine, as well as to Cape Barren Wines at McLaren Vale, while they also produce Chardonnay, Gruener Veltliner and Tempranillo wines under their own brand, ‘Almondcart Wines’.

Kim says he would love to achieve 4 tonne per acre grape yields for most varieties and the Chardonnay did hit 5 t/ac last year, but average yields were around 3.5 t/ac

Scale started to become more noticeable in 2015 and then increased again in the last season, with sooty mould following the same trend.

“I collected adult scale samples nearly every day and, with my microscope, could see precisely when their eggs started to hatch. This occurred just before flowering last season,’’ Kim says.

“When scaley eggs start hatching, the scale crawlers emerge very rapidly, and I didn’t see any eggs that failed to hatch. Seven hundred or more scale hatch from under every adult. This means there could be thousands of crawlers on every shoot unless you have a lot of predators. The crawlers move very slowly – much, much slower than predatory mites – and only make it from the woody tissues and along the new shoots to about leaf seven or eight, where they pack themselves tightly along the sides of the bigger leaf veins.

“A few weeks before harvest, I found that crawlers had fattened up and matured into small adults – dark brown and stuck to the green shoots, petioles or rachises – and these had about 80 or so eggs under them.

“Once the scale has settled onto a leaf, they insert their stylet into the cells and start drawing sap. The stylet is dark, thin and long and they use it to access proteins they need for growth. They require protein to complete their life cycle and draw a relatively large amount of sap for a small amount of protein, so the unwanted liquid, containing significant amounts of sugar is secreted being the honeydew that we see sticking to the leaves.

“Sooty mould grows well on the sugary exudate, so by harvest – as I found – you can have a very dark, sticky and ugly fruit-zone. I had also decided to reduce the amount of copper I used during the season, as I had found alternatives for downy mildew control and this may have contributed to the sooty mould outbreak.

“High levels of sooty mould can cover the leaves and reduce photosynthesis.

“We have sprayed oil for the scale in the past, but when grafting, we pulled back the bark and saw hundreds – and we couldn’t see how oil would kill them. We thought we would need to spray when they are out and about.’’

The Andersons ended up spraying half of their vineyard with Movento® insecticide, which has only been used in winegrapes in recent seasons following registration for control of mealybugs and suppression of scale and thrips.

After leaf uptake, most systemic insecticides are mainly translocated in the plants’ xylem along with water and nutrients and are transported upwards. Movento is translocated in the plants’ phloem as well as xylem, resulting in transportation upwards and downwards to provide protection for most plant parts. Movento, from Bayer, is a two-way systemic insecticide and 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 highly compatible 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.

Movento is also very compatible for tank mixing and requires a recommended adjuvant to help penetrate the leaf material.

“They come back if you don’t kill the progeny,’’ Kim says.

Bayer Commercial Sales Representative Darren Alexander says Movento should be applied in winegrapes no later than E-L18, which is when 14 leaves are separated and flowers caps are still in place but starting to fade from green to orange.

“Growers should apply it from three to four leaf stage through to this pre-flower stage,’’ Darren says.

Kim says the difference in control between the area treated with Movento and the rest of the vineyard was dramatic.

“On one side, the scale went beserk. The infestation went crazy. The Chardonnay was a little more resistant, but the Gruener Veltliner and Pinot Noir were badly affected.’’

“We sold all the grapes from the area not treated with Movento to buyers with a 10% smut rebate – and one winemaker rejected the fruit. Another buyer asked us to spray water before picking to blast the honeydew off and dislodge some of the soot.’’

Kim says depending on conditions in the future, Movento may become part of his regular spray program.

“We will only be using Movento. We should probably hit the vineyard with Movento every two to three years, depending on pest numbers.’’