Farmer Buckley's exploding trousers

From issue 2477 of New Scientist magazine.

In 1931, the peace and quiet of the New Zealand countryside was shattered by a terrifying new phenomenon: suddenly and apparently at random, men's trousers began to explode. Some pairs detonated on the washing line, others as they dried in front of the fire. More seriously, some were occupied when they started to smoulder. At first there were just a few isolated reports, but soon the nation was in the grip of an epidemic of exploding trousers.

The explanation wasn't hard to find. The dangerously self-destructive garments all belonged to farmers who had been trying to destroy the ragwort that was ruining their pastures. This pernicious weed had reached New Zealand decades earlier and was now running riot across the country. The farmer's latest weapon in the war on the weed was sodium chlorate. But when combined with organic material, such as cotton and woollen fibres, the mixture becomes violently explosive.

RICHARD BUCKLEY was lucky. When his trousers blew up he wasn't wearing them. He was badly shocked, but as the Hawera Star reported on 12 August 1931, his quick thinking saved him from serious injury. “While Mr Richard Buckley's trousers were drying before the fire recently, they exploded with a loud report. Although partially stunned by the force of the explosion, he had sufficient presence of mind to seize the garments and hurl them from the house, where they smouldered on the lawn with a series of minor detonations.”

According to the Star, there was only one suspect in the case: sodium chlorate. Until recently the chemical had been more familiar to quarrymen than farmers, but when government scientists declared it the best ragwort killer they had seen, farmers began clamouring for it. Buckley, who farmed in Taranaki, on the western side of the North Island, was just one of a growing number of people falling foul of the new, miracle weedkiller. And not everyone got off so lightly. Some were injured and a few died. In one tragic case, a farm worker who wanted to check on his sleeping baby struck a match to see by. His clothes went up in flames and he died a few days later.

According to New Zealand historian James Watson of Massey University in Palmerston North, there was more to the rash of explosions than dodgy weedkiller and bad advice from the authorities. Ragwort, Senecio jacobaea, was accidentally introduced to New Zealand in the late 19th century and, like so many foreign invaders, quickly became a pest. By the 1920s, the weed was rampant. What made matters worse was that its proliferation coincided with sweeping changes in agriculture. “There was a massive shift from sheep farming to dairying,” says Watson, “and that meant ragwort was an even bigger problem.”

Ragwort contains a battery of noxious alkaloids: it is so toxic that even honey made from its flowers is poisonous. Livestock usually avoid the plant, but once it displaces grass and clover the animals have little else to eat. Sheep can eat it for months before showing signs of illness, but cattle and horses sicken quickly and can die of liver failure. The boom in dairy farming followed the arrival of new technology, first refrigerated ships, then motor vehicles and machines to separate cream from milk. The first refrigerated ships began to carry produce to the UK in 1882. At first they took mainly meat. Shipments of dairy produce only took off once motor vehicles began to replace horses, allowing farmers to get fresh milk to the local dairy factory. When farmers began to separate the cream themselves, the butter factories introduced collection rounds, picking up the cream from the farm gate. As demand and factories grew, dairy farms proliferated and spread into remote areas once thought too marginal to bother with. Between 1899 and 1919 the number of dairy cows doubled. Over the next two decades it doubled again.

“Although partially stunned by the force of the explosion, he had sufficient presence of mind to seize the garments and hurl them from the house” In the past, farmers had grubbed up ragwort by hand, a labour-intensive job that brought only temporary relief: any roots left in the soil simply re-sprouted. But hands were becoming hard to find. Even the unemployed baulked at the hard work and poor pay. By the late 1920s, farmers couldn't even turn to their families. Farmers who put their wives to work in the fields were frowned on. It wasn't respectable. Nor could they rely on their children. School had become compulsory and there were buses to collect children from the farms and inspectors with cars to check on any who didn't turn up.

In any case, the one-man operation was part of the New Zealand farmer's ethos. They adopted the latest labour-saving devices and kept abreast of agricultural research. And they would try anything to get rid of ragwort. “When sodium chlorate came along they saw it as a means of rescue. They would try anything that would save them from hiring labour,” says Watson. The first they heard of the weedkiller was in 1930, when a scientist at the department of agriculture wrote an article extolling its virtues. When a government expert said the weedkiller was far superior at killing ragwort than any other and would, “where properly applied…completely destroy all the plants”, then farmers listened. Within a year, imports soared from almost nothing to hundreds of tonnes.

The accidents started immediately. Mixed with organic material such as the fibres of a farmer's working clothes, sodium chlorate is extremely dangerous, forming compounds that will detonate at the first sign of a spark or a glowing cigarette. Sometimes just a shock or a knock is enough. Washing contaminated clothes made little difference. Why had the government recommended such a dangerous substance? “The scientists were more concerned with how effective it was against ragwort than how dangerous it was,” says Watson. This was a time when arsenic was recommended for getting rid of another serious weed, the blackberry. New Zealand's farmers were prepared to take the risks, and they didn't blame the authorities. “Quite the opposite. They'd have been annoyed if the government had got in the way of them using it,” says Watson. “If they hadn't had it, many would have been forced off the land. The accidents were the price they paid to keep their farms in production.”

Besides, by the time Buckley's trousers hit the headlines in Hawera, farmers must have known of the dangers of sodium chlorate. “Most men smoked then and that would undoubtedly have brought it to their attention,” says Watson. “You can't deal with it for long without discovering that it's dangerous.”

Farmers continued to use the weedkiller until the late 1930s, when word got around that those same government scientists were arguing about just how effective sodium chlorate really was. “Once farmers heard that it wasn't all that good, they started looking for alternatives.” They are still looking. Ragwort remains a serious pest in New Zealand. Today's weapons of choice are not herbicides but insects, the plant's natural enemies in its native Europe. The ragwort flea beetle was introduced in the early 1980s and has been very successful, destroying every single plant in some parts of the country. But the beetles haven't taken to the wetter climate of western New Zealand, where the ragwort problem is as bad as ever.

Earlier this year, Hugh Gourlay of Landcare Research, an independent research institute, began trials with two European species of moth that might be better suited to a wetter climate. The caterpillars of plume moths attack ragwort's roots. Plants attacked by the crown boring moth produce fewer seeds and their growth is restricted. “Studies in Australia suggest that both moths, but especially the plume moth, can reduce ragwort populations by up to 80 per cent in a wide range of climates,” says Gourlay. For now the moths remain confined to quarters until they've proved they won't attack any native plants. This time, scientists are keeping their miracle cure safely under lock and key until they are certain ragwort will be the only victim.

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