One of two plants that mixes concrete in Songjiang District of Shanghai, has been ordered to shut down as its heavy dust is believed to have caused hectares of fruit trees to die after their growth was unnaturally accelerated.

The plant was reportedly still operating yesterday and one owner of a pear orchard has threatened legal action if it does not comply.

Shen Xuefang, 44, the owner, said potential losses on next year's harvest could exceed 400,000 yuan (US$58,561) because chemicals in the dust caused the pears to ripen early.

"The withered branches and dying leaves are all caused by the two plants," said Shen.

"The whole area surrounding the two plants was filled with heavy dust as soon as they began operations."

Liu Fengqiang, deputy director of the Songjiang District Environmental Protection Bureau, said the mixing plant in question had been shut down because it was unlicensed.

Specialists from the bureau checked the two plants last week after they received complaints from farmers.

According to Liu, the prohibited plant was built by the company in August.

It built a plant in 2006 east of Shen's orchard which proved to be environmentally safe, Liu said.

Shen's technical adviser, Fei Libing, predicted an 80-percent loss of next year's pear production due to the shortening of the trees' growth cycle and a nutrient loss caused by dust.

"The dust from the mixing plants contains alkaline and this kills leaves," Fei said.

"Then the dead leaves fall onto the ground and become fertilizer for new trees that are expected to bloom and bear fruit next year, thus unnaturally accelerating growth speed."

However, the company that owns the two concrete-mixing plants refused to admit the heavy dust they produced was the main reason for accelerating the growth cycle of Shen's pear trees with such deadly results.