LUBBOCK, Texas —  The price tag for the drought Texas farmers and ranchers are enduring is mounting with each dry day that passes.

Officials say the losses are $1.5 billion for a six-month period that ended May 1. Most of that is to livestock producers whose grazing pastures are withering through this historic drought. If the drought continues into June, losses for the nation's second largest agriculture producer will top $4 billion. That would make it the costliest season on record.

Meteorologists blame La Nina, a cooling of the Pacific waters near the equator. It's caused extreme drought in Texas and parts of Oklahoma, Louisiana and New Mexico.

About 90 percent of Texas' beef cows are in counties with severe to exceptional drought.

May is typically the wettest month in Texas.