WASHINGTON — U.S. winter wheat crop condition deteriorated slightly from a week earlier, while corn and soybean plantings surged but were still behind the five-year average.

In the 18 major growing states, 45% of the winter wheat crop was rated good to excellent as of May 24, compared with 48% the previous week and 47% at the same time last year, the U.S. Department of Agriculture said in its weekly Crop Progress report. The crop was rated 27% poor to very poor, compared with 26% the previous week and 22% last year.

Winter wheat headed in these 18 states was 68%, compared with 56% a week earlier, 61% last year and an average of 71% over 2004-08.

Planting of spring wheat in the six leading states as of May 24 was 79% completed, the U.S.D.A. said, up from 50% a week earlier but far behind 97% a year ago and 95% as the five-year average for the date. Spring wheat emerged in those states was at 45%, up from 21% the previous week but far below last year’s 73%, or the 77% average.

Corn planting was 82% completed in the 18 major corn states, up from 62% the previous week but still slightly behind last year’s 86% and the 2004-08 average of 93%. Planting in top-producing Iowa was 97% completed, above last year’s 91% and consistent with the average. Planting in Illinois, the second-largest corn growing state, was 62% completed as of May 24, behind 85% last year and 96% as the average for the date but up significantly from 20% a week earlier.

Corn emerged was at 52%, up from 30% a week earlier and above last year’s 48% but below the five-year average of 71%.

Soybean planting in the 18 major states at 48% completed as of May 24 was almost equal to last year’s 49% but was behind the five-year average of 65% for the date, the U.S.D.A. said. Emergence of soybeans was at 17%, ahead of 12% a year earlier but lagging 31% as the 2004-08 average.

Rice planting in the six producing states was 86% completed, below 92% last year and 93% as the 2004-2008 average. Rice emerged was 69%, below last year’s 77% and the average of 82% for the date.