MENGHAI, China (Reuters) - Yan Wenliu leans on the side of his cart as he prepares to leave his sugarcane field in Southwest China, bewildered by the formidable new pest that has ambushed his crops this year.

An armyworm, which usually comes out at night, is seen on sugar cane crop around dusk at a village of Menghai county in Xishuangbanna Dai Autonomous Prefecture, Yunnan Province, China, July 12, 2019. REUTERS/Aly Song

“I don’t know what it is,” says Yan, a 36-year-old farmer from Menghai county in Yunnan province. “But it is bigger than other ones. I have never seen this worm before.”

The creature Yan is unable to name is the fall armyworm, the larva of the fall armyworm moth.

Known locally as the “heart-devouring worm,” the destructive pest has spread more than 3,000 km (1,865 miles) north since migrating from neighboring Myanmar seven months ago, reaching 21 provinces and regions in China and posing a grave threat to grain output.

In Yunnan alone, where the pest struck first in China, some 1.29 million mu (86,000 hectares) had been affected by mid-June, including corn, sugarcane, sorghum and ginger crops.

First found in the Americas, fall armyworm has spread through Africa and Asia since 2016, with the moths flying up to 100 km (60 miles) a night. It can’t be eradicated and its management is both costly and difficult.

This poses a formidable challenge in China where about 90% of crop production comes from small farms of less than a hectare (2.5 acres) and owners lack basic knowledge and resources to tackle the pest.

Beijing warned earlier this year that armyworm was a severe threat to the country’s food security and in May launched a campaign to “snatch grain from the insect’s mouth.”

Millions of yuan have been allocated to affected regions and experts sent to educate farmers.

In Yunnan, the government has set up 3,500 monitoring sites at local agriculture bureaus and conducted frequent field inspections, the provincial agriculture bureau said in an email to Reuters.

Local authorities have also provided training to farmers and pesticide dealers on identification and prevention of armyworm, the bureau added.

(Graphic: Fall Armyworm invasion of Asia IMG, tmsnrt.rs/2XYNbIX)

PESTICIDE OR PENNILESSTo those in Yunnan, the solution to the worm problem seemed obvious - pesticide. “You have to keep spraying chemicals. If you don’t kill the worm, you will end up penniless,” says sugarcane farmer Yan in Mengkang village.

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But paying for the pesticide in the quantities required has left many farmers out of pocket, while a failure to follow the complex regime needed - using different pesticides at different crop growth stages and rotating them to prevent resistance - means the money is often wasted.

“You just can’t kill them,” says Yan Hannen, a 44-year-old farmer, from nearby Nuodong. “I have been farming for 20 years but have never seen this many worms.”

A frustrated Yan applied pesticides fives times to his last crop of sweet corn, but output nearly halved. He has already sprayed his new crop twice, to little effect.

“They told me to use one bucket but I used three. It still did not work. What can you do?” he asked.

Local government has held many meetings to brief farmers on the pest and villagers have improved their approach to using pesticides, said Yan Xiangwa, a village official in Nuodong.

But for farmers who have already battled severe drought this year, the latest threat has put their entire livelihoods at risk.

Villagers tend to give up treatment due to the high cost, the Yunnan provincial government said in a report last month, adding that sufficient human resources for plant protection were also lacking at the local level.

Yu Xianger, another Nuodong farmer, sprayed pesticide on her 2 mu (0.13 hectare) corn field without results and is thinking about finding work in the city.

“The worms have devastated my corn crops this year. And there’s nothing much else I can do,” she said.

(Graphic: Areas suitable for Fall Armyworm , tmsnrt.rs/2XYgvPY)

COMPLEX FIGHT

Experts say the fight against armyworms is difficult and the enemy is a tough one. Adept at hiding, the pest is hard to detect and prefers to venture out at night, to feast on plants and fly to new pastures.

“Local farmers here didn’t use much pesticide before and wouldn’t buy chemicals until they saw the worms, meaning they might have missed the best time to kill them,” said Yao, a sales manager for pesticide supplier Jingbo Agrochemicals Technology Co Ltd in Xishuangbanna, Yunnan province.

The villagers’ slow response to the arrival of armyworm was not helped by the absence of a trapping system involving lights and pheromones that Beijing says is currently being deployed nationwide.

The Yunnan agriculture bureau says it has set up more than 30,000 such trapping systems in the province and is continuously carrying out preventive measures and treatment against the pest, involving chemicals and natural enemies.

While some villages have been badly affected, the government says the province as a whole has been managing the problem.

The damage has been “effectively controlled” in Yunnan, with total corn crop losses limited to within 5%, it said in the email. This year’s summer grain output in Yunnan increased by 16,200 tonnes from the previous year, the bureau said, citing official statistics.

Despite the problems in the country’s south, the outlook for China’s main corn production area in the north is “much better,” says Hu Gao, professor of insect ecology at Nanjing Agricultural University.

Control and prevention measures have given the region, which accounts for more than 70% of China’s corn production, more time to prepare for an invasion.

The worm has yet to reach the northeastern provinces including Heilongjiang, the top grower of the grain, and some experts believe the lower temperatures in the region will protect it from a full attack.

Back in Yunnan, however, farmer Yan Hannei is thinking about switching to other plants like vegetables.

“I am going to lose so much money this year,” he says. “What can you do? I can only stop growing corn and grow something else.”