Harley-Davidson (HOG) is retreating after Citigroup, in a note to investors earlier today, estimated that the company's U.S. sales growth slowed down significantly in June, compared with the same period in 2011. After conducting dealer checks, the firm believes that the motorcycle maker saw its U.S. sales growth slow dramatically to a low single digit percentage increase last month, versus a high teen percentage increase in June 2011. The firm adds that Harley-Davidson's U.S. retail sales are on track to rise 4%-5% in the second quarter, down from a 26% surge in the first quarter. The warmer winter weather may have caused some customers to buy the company's motorcycle's earlier in the year than usual, said Citi, which maintains a $61 price target and Buy rating on the shares. In early trading, Harley-Davidson dropped $1.43, or 3.04%, to $45.62.