Bayer AG (BAYRY) shares slumped to a four-month low in Frankfurt Thursday after the German drug and pesticides maker lowered its full-year sales and earnings estimates thanks in part to a surging euro and challenging business conditions.

Bayer said it expects full-year sales to rise to €49 billion ($57.43 billion), down 4% from its previous guidance and forecasts adjusted operating profit to grow "by a high-single-digit percentage" compared to its prior aim of a growth rate in the "low teens". The group said its planned acquisition of Monsanto remains on track and that its "making progress in our discussions with regulatory authorities"

Bayer shares were marked 3.36% lower in the opening hour of trading in Frankfurt and changing hands at €107.85 each, the lowest since April 26, extending their year-to-date decline to 9.6%.

Bayer said adjusted earnings for the three months ending in June rose modestly from the same period last year to €3.06 billion while overall group sales edged 3% higher to €12.19 billion.

The outlook changes followed the company's profit warning last last month, which it said was based on weakness in a key market in Brazil and the recent rise in the European single currency.

The Leverkusen, Germany-based group said at the time that weakness in its crop science market in Brazil would lead to a a €300 million to €400 million hit to its full-year earnings and added that "unfavorable currency developments" and a weaker-than-expected performance in its consumer healthcare division would also trim its bottom line.

The euro, Bayer's reported currency, has risen to a two-and-a-half year high of 1.1770 against the U.S. dollar over the month, capping its biggest quarterly gain in at least four years.

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