Effects of Climate Change on Pests

Lincoln University postgraduate research fellow, Dr Marco Jacometti, this year started a three-year study which will artificially create the climatic conditions that the latest climate change models are forecasting for vineyards.

He will then look at whether mulches and inter-row plantings of buckwheat will reduce numbers of common vineyard pest, the light brown apple moth (LBAM), by encouraging species which parasitise or predate them. The study also investigates whether these and other enhanced ecosystem services could be harnessed to reduce the incidence of botrytis.

LBAM damage grapes, increasing their susceptibility to grape bunch-rot, Botrytis cinerea, which each year costs the New Zealand grape-growing industry around $5 million in disease control and damaged crop.

Climate change will make the climate in most New Zealand horticultural areas warmer, drier and more variable due to an increase in the frequency of North West wind flows. These conditions will probably promote increased populations of vineyard pests and diseases at a time when the industry is rapidly running out of chemical controls.

This is due both to chemicals becoming less effective due to a continual build-up of resistance, and to markets becoming increasingly averse to chemical residues in food and beverage products. UK store Marks & Spencer, for example, tests for a minimum of 155 different pesticide residues.

New Zealand Winegrowers recognises the opportunity for wine producers to respond to clear market signals and achieve "nil detectable residue" wines while not compromising pest control, disease suppression and wine quality. Chairman, Stuart Smith, implores growers to use or at least trial sustainable practices in their vineyards, such as biological rather than chemical control of pests and diseases.

Winegrowers has set a target of seeing all businesses in the industry - predicted to be worth $1 billion this year - in accredited sustainability schemes by 2012.

However, there is growing concern that the biological control/natural systems which regulate pests and diseases may destabilise in climate change. The result could be increased pest pressure and disease epidemics; potentially devastating in monocultures like vineyards.

Marcos trial is replicating the effects of climate change in vineyards, enclosing small areas to lift temperatures 2-2.5 degC on average, with +4-6deg C peaks. The sun sails first trialed increased temperature by only about 0.5degC. Ventilated poly-houses are now being used. A proportion of these are made from plastic sheets plus quarantine mesh and a proportion from mesh only. All can have their hems lifted to allow insects in and out, meaning Marco will be able to look both at direct heat effects including possible changes in population dynamics while also allowing for natural behaviour.

The aim is to investigate biological tools for reducing populations of pests which damage grapes, making them vulnerable to botrytis infection, without resorting to chemicals. This will be vital, as global warming lifts the risk of disease in vineyards, chemical controls lose their efficacy, and the market demands residue-free wines.

Trial areas will be managed according to standard practice, or have ecosystem services enhanced by under-vine mulching and inter-row plantings of buckwheat.

These treatments may increase the prevalence of European earwigs - known nocturnal predators of LBAM - and Dolichogenidia tasmanica, a common LBAM parasitoid. Pest population densities and botrytis severity will be assessed inside and outside the climate chambers, before and after harvest.

While this is a new study, it builds on a previous Lincoln trial which demonstrated that buckwheat plantings can reduce LBAM numbers below an economic threshold by providing a favourable habitat for Dolichogenidia tasmanica.

Marcos doctoral research investigated various vineyard mulches, finding that they reduced botrytis pressure by breaking the lifecycle of this fungal disease.

Botrytis over-winters on vine debris in the vineyard. Marco found that mulch takes up space which otherwise could have been occupied by botrytis. It also changes Cation Exchange Capacity (CEC) activity in the soil, making calcium more available to vines which in turn strengthens grapes skin. This reduces susceptibility to botrytis infection, both because the disease is less likely to enter the fruit and also because it becomes more difficult for disease-carrying young LBAM caterpillars to penetrate.

The mulches were made from three waste-stream materials; shredded office paper; fermented marc (the pips and skin waste left behind after crushing grapes for winemaking) and mown inter-row grass. These different materials had different effects, with office paper causing vines to become less vigorous making it easier to balance vines vegetative and fruit production.

Marco is looking at ways of encouraging European earwig presence in vineyards. Mulches may help by providing resources like alternative food when LBAM populations are low, and increased shelter.

The study will also take a close look at earwigs lifecycle and lifestyle, to learn more about their potential as a beneficial insect.

Once techniques for replicating climate change have been perfected in the Lincoln vineyard, its planned to extend the study to commercial vineyards. In Hawkes Bay, Marco hopes to look at bio-controls for leafroll virus vector, citrophilus mealybugs, including parasitoids and beneficial ants.

This research is being supported by the Foundation for Research Science and Technology (FRST).