December 23, 2015

Overuse of pesticides is devastating China’s crops, study says

While the Great Recession is over, many of its aftereffects are still being felt—especially in China, where a shift in agricultural practices driven by the economic crisis may have devastating results, according to a new study that spanned 10 years.

In the early 2000s, the Chinese government decided to invest in chemical production facilities, which served them well on the international market until the global recession. Then, as exports plummeted, these facilities began to flood local markets with their products—including now-cheaper insecticides. Farmers began spraying their fields in earnest.

But, according to a study published in Ecological Applications, this sudden surge in pesticide usage had an unusual effect: While helping to eliminate much of a one of the top 100 invasive species, a pest known as the whitefly, it appears to actually have driven the growth of a different subtype of the same species.

This would all be fine and dandy, except for one enormous issue: This now-booming subtype of whitefly is an enormous plant disease carrier—and as of 2012, it had become dominant in all but two of the 28 provinces and territories examined. (Six, including contentious Tibet and Taiwan, were not included in the study.)

Pesky pesticides (or something like that)

The whitefly is not native to China, and has actually invaded 60 other countries in the past two decades as well. These pests have caused enormous agricultural losses, and naturally many countries have turned to pesticides to reign in the damage—but when they are used improperly, it causes even more problems.

This seems to be the case in China, where the majority of crops come from small family farmers. These farmers are generally less educated by their government in terms of proper insecticide use. And because of this, and the sudden availability of pesticides, many have been dousing their crops to eradicate the whiteflies.

But, as the international team of researchers discovered, the two subspecies of whiteflies prominent in China react differently to pesticides. In areas without the chemicals, the non-disease carrying subtype (known as MEAMI, the Middle East-Asia Minor I subtype) almost always out-competes the subtype that spreads plant viruses. But when faced with three different insecticides in their study on tomato and cucumber plants, the MED flies were generally resistant to them—and began to exclude the MEAMI flies entirely.

In fact, other studies found that MED (the disease-carrier) is 1200-1900 times more resistant to certain pesticides than MEAMI—which was clearly reflected in its spread across China. As the pesticide use shot up, MED began to dominate.

And as mentioned before, unlike MEAMI, MED is a strong disease vector. In particular, it carries tomato yellow curl leaf virus, a devastating crop disease. In India—which has a farming infrastructure similar to China—outbreaks of the virus lead to 50-100 percent yield losses of tomato crops.

Or, to put it in a different perspective: In the early 2000s, this virus led to a $300 million loss of crops in the US and Europe.

But MED can carry hundreds of viruses that can harm crops, not just tomato yellow curl leaf virus—making it an even more worrisome threat.

There is likely to already be a good amount of damage wrought throughout China's crops, but the Chinese government doesn't make such figures publicly available. However, as the pest has touched (two out of 28) or dominated (26 out of 28) every single studied province, it's safe to say it's more than a small issue.

The problems don’t end there, though: One specific family of pesticides—neonicotinoids—has been tied to the alarming plummet in pollinator populations, like bees. In fact, the European Commission has approved a two-year ban on their widespread use, in efforts to combat the decline of pollinators.

However, Chinese farmers continue to increase their use neonicotinoids and other synthetic insecticides, which as of yet have unknown ecological effects. Meaning it’s not just their crops that are in danger, but their pollinator populations as well—and the other areas of the ecosystem downstream from both of them, too.