WASHINGTON — Old crop corn and soybean futures posted strong gains Monday while wheat futures were modestly higher, with all three trading mixed overnight. Prices were supported by concerns about late planting of corn, soybeans and spring wheat, by tight old crop supplies of corn and soybeans, and by the poor condition of the hard red winter wheat crop.

In its May 13 Crop Progress report, the U.S. Department of Agriculture said corn planted in the 18 major states as of May 12 was 28% completed, up from 12% a week earlier but far behind 85% at the same time last year and 65% as the 2008-12 average for the date. Planting in top producing Iowa was only 15% completed compared with 79% as the average, and in Illinois, the second largest corn state, planting was 17% completed compared with 64% as average.

According to the University of Illinois, corn planted in that state after May 10 may see an 8% yield loss, after May 20 a 15% loss and after June 1 a 25% loss.

Corn emerged in the 18 states was 5% as of May 12 compared with 52% a year earlier and 28% as the five-year average.

Soybean planting stood at 6% as of May 12 compared with 43% last year and 24% as the average, the U.S.D.A. said. Planting in top producing Iowa was only 1% completed compared with 30% as the average for the date, and planting in No. 2 Illinois had yet to begin compared with 19% as the average.

Better progress was made in spring wheat and sugar beet planting during the past week. Spring wheat planted in the six major states advanced to 43% completed from 23% a week earlier, but remained well behind 92% a year earlier and 63% as the five-year average. Spring wheat was 10% emerged in the six states, compared with 63% last year and 32% as the average.

Sugar beet planting in the four major states advanced to 62% completed by May 12, up from 24% a week earlier but lagging 100% at the same time last year and 78% as the average for the date.

Winter wheat conditions nearly were unchanged for the 18 state aggregate with wheat in most hard red winter states still mostly rated poor to very poor and wheat in most soft winter states rated mostly good to excellent. Overall, winter wheat was rated 32% good to excellent, unchanged from a week earlier but well below 60% last year, and 39% poor to very poor, also unchanged for the week but well above 14% a year earlier.

Winter wheat headed by May 12 was at 29% in the 18 major states, also well behind 73% a year ago and 51% as the 2008-12 average for the date.