New Zealand's crops could be hit by more - and more serious - disease as climate change brings harsher, longer droughts.

A team of Kiwi scientists say an increase in droughts over the coming decade is likely to increase the severity of a wide range of diseases affecting our vital primary industries.

The researchers - from the Bio-Protection Research Centre, Scion, Lincoln University, AUT University, Landcare Research and the University of Auckland - analysed the potential impact of climate-change-induced drought on several commercial plants and their diseases.

Their study, just published in the journal Australasian Plant Pathology, found that in most instances "increased drought is expected to increase disease expression".


The likely negative effects of droughts included a "predisposition of hosts to infection through general weakening and/or suppressed disease resistance", they wrote.

More frequent and more severe droughts could also lead to "emergence of enhanced or new diseases of plants that can reduce primary production".

"New plant disease pressures are expected to occur… with potentially devastating impacts for New Zealand's productive sectors."

Among the negatives, there were some positive spin-offs of a droughtier future.

"Drought may reduce the severity of some diseases, such as Sclerotina rot of kiwifruit and red needle cast (RNC) of radiata pine," they said.

And in some cases it could "activate systemic defence mechanisms resulting in increased resistance to infection".

In an extended case study the authors said that the effects of increased drought on New Zealand's Pinus radiata industry would depend on many factors, including whether drought happened early or late in the season.

"There is urgent need to study the impacts of the different levels of drought and different levels of RNC severity to understand the thresholds at which radiata pine plantations would still accomplish their economic and ecological roles."


Lead author Dr Steve Wakelin, of the Bio-Protection Research Centre and Scion, said it was essential that more research was carried out so each industry could prepare for the effects of drought.

"Many industries, such as agriculture and horticulture, may have time to gradually change over the next 20 or 30 years, to avoid the worst effects of drought or even take advantage of any opportunities the changing climate may bring.

"However, plantation forestry does not have the luxury of flexibility. What is planted now will need to not just survive but thrive in whatever climate and disease conditions are prevailing in the next 20, 30, or 40 years.

"It's essential that primary industries with a long production cycle start assessing and addressing the risks and opportunities a much drier climate will bring."

A previous New Zealand study found climate change could combine the same weather patterns that led to 2012-13's widespread $1.3 billion drought.

It also found there was now a 50 per cent greater chance of exceptionally high pressure systems occurring over New Zealand in summer than was the case a century ago.

New Zealand and climate change

• Under present projections, the sea level around New Zealand is expected to rise between 30cm and 100cm this century. Temperatures could also increase by several degrees by 2100. Climate change would bring more floods; worsen freshwater problems and put more pressure on rivers and lakes; acidify our oceans; put even more species at risk and bring problems from the rest of the world. Climate change is also expected to result in more large storms compounding the effects of sea-level rise.

• The latest greenhouse gas emissions inventory, which gives a picture of how much human-generated greenhouse gas is being emitted into and removed from our atmosphere, shows emissions as at 2016 have increased from 1990 levels by 19.6 per cent. New Zealand has pledged to slash emissions by 30 per cent below 2005 levels, and 11 per cent below 1990 levels, by 2030.

• The new coalition Government has promised greater action, with a proposed new Climate Commission and Zero Carbon Act and goals for a carbon-neutral economy by 2050 and 100 per cent renewable energy by 2035.