* Fiber slumps more than 7 pct in May
* Index fund roll seen adding pressure
* Speculators cut net long to three-week low -CFTC

NEW YORK, May 31 (Reuters) - ICE cotton sank for a ninth
straight session on Friday in its longest slide in three years
to post the largest monthly drop since September, after long
liquidation erased gains.
The most-active July cotton contract on ICE Futures U.S.
fell 0.77 cent, or 0.97 percent, to settle at 79.36 cents
per lb, after falling to a four-month low of 79.30 cents.
It was the front-month contract's longest stretch of
a down trend since June 2010.
Spot prices plunged more than 7 percent in May, the
second straight monthly loss after six months of gains.
"The funds are rolling out of July. As they do that, it's
weighing on the market because they're struggling to find
buyers," said John Flanagan of Flanagan Trading Corp. in North
Carolina, referring to the index fund roll out of the
most-active contract.
The Thomson Reuters-Jefferies CRB index, a
benchmark for global commodities, declined in May as investors
turned to equities markets.
Speculators cut their bullish bet in cotton futures and
options to a three-week low in the week ended May 28, U.S.
government data showed on Friday.
Prices rallied about 18 percent during the first quarter of
the year, after posting two years of losses, as speculators
boosted their bullish cotton stance to five-year highs in March.
The ICE December contract closed down 0.77 cent, or
0.9 percent, at 82.06 cents per lb.
U.S. government weekly export data showed that both sales
and shipments increased in the week ended May 23 from the
previous week.
Cotton bulls say the falling prices may spur more mill
buying and strain tightening global supplies outside of China,
the world's largest textile market.
The global forecast is that record inventories will be held
by the end of the next crop year through July 2014. More than
two-thirds of those are expected to become part of China's
stocks and are considered unavailable to the global marketplace.
Prior to the first quarter gains, cotton posted two years of
losses, as lower-priced, synthetic alternatives eroded demand,
and global surpluses grew.