Afternoon Market Losers

GenMark Diagnostics GNMK dropped 25.12 percent to $11.33 after competitor Luminex's LMNX Natural Molecular released a new product.

Lululemon Athletica LULU fell 16.40 percent to $68.86 on news of CEO Christine Day's resignation.

LDK Solar LDK tumbled 10.49 percent to $1.47 after posting a wider first-quarter loss and declining revenues.

Real Goods Solar RSOL is down 10.30 percent to $2.96, likely on sector news of LDK's missed earnings.

Navistar NAV slumped 6.70 percent to $32.00 on Q2 results.