US STOCKS-Wall St slumps as weak Chinese data adds to growth fears
* World stocks tumble towards worst week of the year
* Apple weighs the most on the Nasdaq, S&P
* All 10 major sectors fall
* Deere falls after reporting drop in profit
* Indexes down: Dow 0.98 pct, S&P 0.94 pct, Nasdaq 1.35 pct (Updates to open)
By Tanya Agrawal
Aug 21 (Reuters) - Wall Street slumped at the open on Friday, falling for the fourth straight session, as more grim data from China spooked investors already worried about the pace of global growth.
The Dow Jones industrial average was poised to for its sharpest weekly fall since November, 2011. The Nasdaq composite and the S&P 500 were on track for their steepest weekly fall since May 2012.
All 10 major S&P sectors were in the red, led by the consumer sector, and seven of the 10 were down more than 0.8 percent. Continuación...