New Zealand's land-based primary industries need to get ready for more and more serious crop disease as climate change causes more and longer droughts, according to new research.

In the journal Australasian Plant Pathology, the authors say that climate change is expected to bring more droughts in many parts of New Zealand, and more droughts are "likely to increase the severity of a wide range of diseases affecting the plant-based productive sectors".

Scientists 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. They found that in most instances "increased drought is expected to increase disease expression".

The probable negative effects of drought include "a predisposition of hosts to infection through general weakening and/or suppressed disease resistance".

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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," the authors said.

But the news is not all bad.

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

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

In an extended case study the authors said 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.

Lead author Dr Steve Wakelin, of the Bio-Protection Research Centre and Scion, said it was essential 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."