Pests that attack the plants humanity relies on for food have been creeping poleward at an average rate of almost 2 kilometers (3 miles) each year for the last 50 years, according to a new study of hundreds of harmful organisms in the journal Nature Climate Change.

The primary cause of the spread of the insects, fungi and viruses is humans transporting them with crops and farming equipment, but the broad swath of species moving poleward also appears to be riding on the back of global warming, which is making it possible for those pests to take root in places that were just too cold in bygone times, say the researchers.

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In all, 612 crop pests and pathogens were investigated by the University of Exeter's Daniel Bebber, Sarah Gurr and Mark Ramotowski of University of Oxford. This is the first study of so many pests -- including fungi, bacteria, viruses, viroids, water molds, insects and nematodes -- to look for a climate-related trend. What they found was that the average poleward shift was 2.7 kilometers (1.7 miles) per year since 1960, with significant differences among the pests. There were a few nematodes and viruses that were moving the other way, but they were in the minority.

The danger the pests pose is alarming because most of the largest crops grown in the world today are not really up for a fight against new pathogens, explained Gurr, who is a fungi researcher.

"In the process of boosting food production we have also created vast monocultures of, for instance, wheat," said Gurr. "These genetically limited plants are very vulnerable."

The situation is not a lot different than when the water mold Phytophthora infestans caused the Irish potato famine of the 1840s, or when the fungus Helminthosporium oryzae brought about the 1943 Great Bengal Famine, she said. By creating vast fields of genetically limited and identical plants, we've set the stage for another disaster.

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"We've skewed the arms race to the fungi," Gurr said, adding that there is a natural reservoir of between 1.5 and 5.1 million species of fungus out there.

What's more, while farmers are quick to spot a new pathogen, the poleward spread is not just happening on farms.

“What worries me is that there are a lot of these moving into natural systems that we don't see," said entomologist John Trumble of the University of California at Riverside. Nobody is monitoring natural systems with as much attention as they do for simply even a field of cantaloupes, for example.

Already forests in North America have seen this in many forms, Trumble explained, with newly introduced pests removing entire species from some landscapes.

Fortunately, we are not helpless against the assault, said Gurr. The best defense is more frequent and better inspections and more care when transporting materials and plants. Some countries, like Australia, do this very well and can serve as models for others, she said. Considering what's at stake and how global warming is helping the pests, there's no time to lose.