* 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.
Disney, a Dow component, slumped 2.5 percent to $98.51 after a Cowen and Company price target cut. Disney weighed the most on the consumer index.
Apple's fell 1.4 percent to $111.10 as investors continued to fret over the company's prospects in China, a key growth market for the iPhone maker. The stock was the biggest drag on the S&P and the Nasdaq.
Data from China showed its giant manufacturing sector shrank at the fastest pace since the depths of the financial crisis in 2009, exacerbating worries about its health that have been preying on economist's minds for months.
That decline comes on the heels of weaker-than-expected economic data in July, plus this month's yuan devaluation and a stock market plunge. Shanghai stocks dropped another 4 percent on Friday, bringing losses for the week to 11 percent.
World stock markets tumbled towards their worst week of the year on Friday and commodities had another bruising day.
"There are many, and legitimate, contributing factors to the global economic slowdown narrative. These include China-related issues, such as the recent devaluation of its currency, the stock market's boom and bust in recent months, and slower GDP growth," said Nigel Green, Chief executive of deVere Group.
"I believe that this volatility is likely to remain with us, at least until the end of the year ... But for most long term investors, fears of a near-term financial apocalypse are overdone."
At 9:36 a.m. ET (1336 GMT) the Dow Jones industrial average was down 166.69 points, or 0.98 percent, at 16,824.
The S&P 500 was down 19.08 points, or 0.94 percent, at 2,016.65 and the Nasdaq composite was down 65.72 points, or 1.35 percent, at 4,811.77.
The consumer discretionary index's 1.45 percent fall lead the decliners among the 10 S&P sectors.
Wall Street had tumbled on Thursday, with the S&P 500 and the Dow closing in the red for the year, on concerns that the decelerating Chinese economy would translate into slower global growth.
Concerns regarding China's slowing growth and its impact on the global economy and a U.S. inflation rate below the expected target has caused some investors to scale back bets that the Federal Reserve will raise interest rates in September.
Netflix fell 5.2 percent to $106.73 as the weakness in media stocks from Thursday looked set to continued.
Deere fell 5 percent to $86.04 after the maker of John Deere tractors, reported a 40 percent fall in quarterly profit.
Salesforce.com rose 3.7 percent to $70.25 after it raised its revenue forecast for the year, while HP rose 2.4 percent to $27.98 even though its revenue fell for the fourth straight quarter. (Reporting by Tanya Agrawal in Bengaluru; Editing by Savio D'Souza)