Treasury Wine Estate shares have plunged almost 20 per cent after the owner of the famous Penfolds label warned it would miss profit targets due to problems its US wine business.

The global wine group’s chief executive, Michael Clarke, blamed the downgrade on changes in its US executive team, the rise in popularity of private labels among American wine drinkers, and discounting.

Recent drought, heat and fires in Australia will also impact on the cost of the local vintage, which is currently in harvest, the winemaker said in an overnight announcement to shareholders.

However, the biggest impact is from its Americas region, which reported a 17 per cent drop in earnings before interest and taxes for the first half of 2019/20 to $98.3 million.

The downgrade means the company now expects earnings growth of only 5 per cent to 10 per cent for the full financial year, instead of 15 per cent to 20 per cent as previously advised.

The wine group’s shares were down $3.54, or 21.22 per cent, at $13.14 at 1115 AEDT.