Prices for U.S. farm exports dropped in July by the most in more than six years as a trade war with China heated up, Labor Department figures showed Tuesday.

Agricultural export prices fell 5.3 percent from the prior month, the biggest drop since October 2011, as soybean prices plummeted 14.1 percent. Export prices for corn, wheat, fruits and nuts also slumped in July. The overall export price index dropped 0.5 percent, the most since May 2017, the department said. The figures exclude the price effect from any tariffs.

China in July slapped 25 percent tariffs on American soybeans and also targeted other farm goods in retaliation for U.S. duties on a range of merchandise. The world’s biggest buyer of soybeans has shunned U.S. supplies amid the escalating trade conflict, threatening to curb exports after the harvest.

The report also showed that import prices were unchanged from the previous month, matching the median estimate of economists. Prices were up 4.8 percent from a year earlier, the biggest advance since 2012, driven by a 40.7 percent rise in fuel import prices.