By Marcy de Luna HOUSTON (Reuters) -Oil prices tumbled 5% in volatile trading on Tuesday on demand concerns after the International Monetary Fund (IMF) reduced its economic growth forecasts and warned of higher inflation. Prices fell despite lower output from OPEC+, which produced 1.45 million barrels per day (bpd) below its targets in March, as Russian output began to decline following sanctions imposed by the West, according to a report from the producer alliance seen by Reuters. Russia produced about 300,000 bpd below its target in March at 10.018 million bpd, based on secondary sources, th…