KANSAS CITY — Continuing deterioration of the U.S. corn and soybean crops was evident in the latest Crop Progress data from the U.S. Department of Agriculture for the week ended July 22. Spring wheat crop conditions declined modestly as well.

Row crops have been under assault by a severe drought that is considered the worst in more than 50 years. Damage to the corn crop is viewed as probably irreversible while the soybean crop is still at a stage where rainfall may improve crop conditions.

In the 18 major corn growing states, a total of 26% of the corn crop was rated good to excellent, down from 31% the previous week, the U.S.D.A. said. The proportion of the crop that was very poor to poor surged to 45% as of July 22, up from 38% in the previous week. A year ago in the same week, 62% of the crop was rated good to excellent and only 14% was very poor to poor.

As of July 22, a total of 31% of the soybean crop was rated good to excellent in the 18 major soybean growing states, down from 34% the previous week, the U.S.D.A. said. A total of 35% of the crop was in very poor to poor condition during the latest week, up from 30% very poor to poor in the previous week. In the same week a year ago, 62% of the soybean crop was rated good to excellent and only 11% was very poor to poor.

In contrast to corn and soybeans, the condition of the spring wheat crop remained strong, although not as favorable as a year ago. The U.S.D.A. said 60% was in good to excellent condition in the six major spring wheat states, down from 65% in the previous week and 74% at the same time a year ago. A total of 11% of the crop was in very poor to poor condition as of July 22, up from 8% in the previous week and 5% in the same week a year ago, the U.S.D.A. said.

A majority of the 2012 corn crop has gone through the silking stage as of July 22, well ahead of average. A total of 86% of the crop had silked as of July 22, up from 56% in the same week a year ago and 59% as the 2007-11 average for the date. A total of 22% of the crop had reached the dough stage in the latest week, up from 7% in the same week a year ago and 9% as the five-year average. Six per cent of the crop was dented in the 18 states, up from 2% a year ago and as the 2007-11 average, the U.S.D.A. said.

Soybeans have been blooming ahead of schedule in 2012. In the 18 major soybean states, a total of 79% of the crop had bloomed, up from 54% in the same week a year ago and above the average in 2007-11 of 60%. The pod setting stage had been reached in 36% of the crop, up sharply from 13% in the same week a year ago and from 19% in 2007-11.

The spring wheat harvest was under way ahead of schedule, the U.S.D.A. said. In the six main spring wheat states, 12% of the crop had been harvested as of July 22, up from zero as of July 22, 2011, and as the 2007-11 average.