MADIKERI India (Reuters) - It's 10 o'clock in the morning and a dozen workers are uprooting coffee plants, piling them in the corner of a field at M.G. Bopanna's plantation in Karnataka where they lie ready to be burned.
The plants are bursting with green cherries but inside their hard bark lurk destructive white stem borer beetles. The bushes have to be destroyed to prevent the tiny winged creature from threatening Bopanna's entire crop of arabica coffee.
The beetle, which bores through plants' bark and feeds on their stems, is thriving this year due to unusually warm weather and scant rains in arabica growing areas in India, the world's sixth biggest coffee producer.
If the hot spell continues and the pest continues to spread, India's coffee crop could fall to its lowest in 17 years when the harvest starts in October, pushing up global prices that are already rallying due to drought in top exporter Brazil.
The damage caused by the beetles is so severe that Bopanna has hired an excavator to uproot affected bushes on his 63 acre plantation at the hill station in the tropical forest of the Western Ghats, west of high-tech hub Bangalore.
"Every time we think we have uprooted all the infected plants, then after a few weeks we find more," says Bopanna, 69, who has tended the plantation bought by his father for nearly four decades.
"Earlier whenever there was an outbreak, we used to uproot five to 10 plants per acre. This year I have uprooted more than 200 plants per acre," he said.
There is no effective pesticide to control white stem borers, so the state-run Coffee Board advises farmers to uproot and burn infested plants to limit their spread.
"You may take all precautions, but if your neighbour is lethargic then white stem borers will fly from your neighbour's plantation," said N. Bose Mandanna, a grower from Madikeri who has removed all affected plants from his 34 acre plantation, five kilometres west of Bopanna's field.
In most years heavy rainfalls and low temperatures restrict the spread of the white stem borer. But this year southern Karnataka state's Kodagu and Chikmagalur districts, which account for two-third of India's total coffee production, have received half the usual rainfall since the start of monsoon season on June 1.
The state run weather department said earlier this month that rainfall in July and August is expected to remain below average.
"The pest infestation will rise quickly if rainfall remains subdued in the next few weeks," says Mandanna, a fourth-generation arabica coffee planter.
India's arabica coffee production could drop as much as 20 percent in the 2014/15 season to 60,000-70,000 tonnes, said a spokesman at Ruchi Soya, a coffee exporter.
That would pull down India's total coffee output, three quarters of which is exported, to 260,000 tonnes, the lowest level since 1997/98, estimates Ruchi Soya.
Italy, Germany and Belgium are the main buyers of Indian coffee and usually pay a premium for it over global prices. Starbucks, J.M. Smucker Co and Kraft Foods Group are leading buyers of arabica.
Bopanna and other farmers are replacing affected plants with new seedlings, cultivating instead a robusta variety that is cheaper than arabica but resistant to white-stem borer.
"I would love to have an entire coffee plantation with arabica, but I have to consider earnings as well. How I would pay workers if the pest damages my entire arabica crop?" asks Bopanna, who is planning to convert 16 acres to robusta this year.
Arabica coffee is typically roasted and ground for brewing and can range widely in quality, with some reaching the highest levels. Robusta, on the other hand, is more bitter and either processed into instant coffee or added to a roasted blend to reduce the cost.
India, which started coffee cultivation in 1670 with seven smuggled beans, produced mainly arabica until a few decades ago. Now arabica accounts for just one third of India's total output compared to 82 percent in 1950.
That share will fall further unless the Coffee Board develops new arabica varieties that can withstand white stem borer, says Marvin Rodrigues, former chairman of the Karnataka Planters' Association.
"Farmers can't absorb shocks of white stem borer," said Rodrigues said.
"It is not hurting just one year's income; it is squeezing four year's earnings."
Coffee seedlings start flowering and produce cherries only after four to five years, meaning the impact of this year's pest infestation will persist in India's arabica production for at least that long.
Besides, arabica is also a labour-intensive crop at a time when wages are rising quickly due to labour shortages yet yields around half the cherries of robusta.
"Though robusta prices are lower than arabica, it is economical to have robusta. You can recover at least input cost even during bad year," said Sundaram Ramasamy, executive director at Amrutha Coffee.
For Bopanna though, this year's crop will be costly.
"Hopes of a bumper crop flourished with widespread flowering in March, but white stem borer ruined those expectations," he said.
"I was expecting a crop of 15 tonnes, now harvesting 10 tonnes seems difficult."
Reporting by Rajendra Jadhav; Editing by Rachel Armstrong