(Reuters) - Treasury Wine Estates Ltd , the world's second-largest wine company, warned on Monday its first-half earnings would slide 20 percent, as poor weather and higher corporate costs dragged, pushing its shares down eight percent. Treasury Wine, which was spun off from brewer Foster's Group last year, had warned in August that earnings growth would slow in 2013 due to higher costs as it builds inventory of premium wines. Investors were taken by surprise, sending shares in the maker of Penfolds, Beringer and Wolf Blass down 8.4 percent to A$5.04, its biggest one-day slide since listing.