KANSAS CITY, Mo. — Continuing deterioration of the US corn and soybean crops was evident in the latest Crop Progress data from the US Department of Agriculture (USDA) 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 percent of the corn crop was rated good to excellent, down from 31 percent the previous week, the USDA said. The proportion of the crop that was very poor to poor surged to 45 percent as of July 22, up from 38 percent in the previous week. A year ago in the same week, 62 percent of the crop was rated good to excellent and only 14 percent was very poor to poor.

As of July 22, a total of 31 percent of the soybean crop was rated good to excellent in the 18 major soybean growing states, down from 34 percent the previous week, the USDA said. A total of 35 percent of the crop was in very poor to poor condition during the latest week, up from 30 percent very poor to poor in the previous week. In the same week a year ago, 62 percent of the soybean crop was rated good to excellent and only 11 percent 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 USDA said 60 percent was in good to excellent condition in the six major spring wheat states, down from 65 percent in the previous week and 74 percent at the same time a year ago. A total of 11 percent of the crop was in very poor to poor condition as of July 22, up from 8 percent in the previous week and 5 percent in the same week a year ago, the USDA 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 percent of the crop had silked as of July 22, up from 56 percent in the same week a year ago and 59 percent as the 2007-11 average for the date. A total of 22 percent of the crop had reached the dough stage in the latest week, up from 7 percent in the same week a year ago and 9 percent as the five-year average. Six per cent of the crop was dented in the 18 states, up from 2 percent a year ago and as the 2007-11 average, the USDA said.

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

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