(Recasts, adds detail on causes of decline, context)
SANTIAGO, May 30 (Reuters) - Chile reported an unexpectedly low wine harvest in April, contributing to the country's weakest industrial output reading in nearly three years, according to government data published Tuesday.
Chilean manufacturing production fell 7.5 percent in April from a year earlier, significantly underperforming market expectations, with a Reuters poll forecasting a 1.5 percent decline.
It was the biggest year-on-year decrease since August 2014.
Calendar effects - there were three fewer working days than a year ago - took their toll, but the statistics institute INE also cited lower wine production due to a shortened harvest and falling demand, with weather conditions also affecting some fruit and vegetable output.
A torrid southern hemisphere summer forced the wine harvest in Chile to begin earlier than usual, although wine-growers to date have said they did not expect that to affect volumes.
A competitive market and falling demand in Britain due to a weaker pound have also hurt Chilean wine exports.
Copper makes up over half of Chile's export earnings, but the South American country is also an important producer of wine, fruit, salmon and paper.
Copper production fell 1.8 percent year-on-year, INE also reported on Tuesday, as the giant Escondida mine slowly ramped back up output after a strike in February and March. (Reporting by Rosalba O'Brien; Editing by Bill Rigby)