WASHINGTON (MarketWatch) - The nation's manufacturers cut back production at a much faster pace than expected in September, the Institute for Supply Management reported Wednesday. This is the lowest level since October 2001. The ISM index plunged to 43.5% in September from 49.9% in August. This is the biggest drop in the index since 1984. The drop surprised economists. The consensus forecast of estimates collected by Marketwatch was for the index to slip only a bit to 49.6%. Readings below 50 indicate contraction. The ISM index has been holding near 50 since the summer. The previous low this year was 48.3 in February. Economists said the ISM index was near recessionary levels.