WASHINGTON, D.C., U.S. — Producers used a recent multi-day window of warm, dry weather to make major progress — 43 percentage points in one week — in the planting of the 2013 corn crop, the U.S. Department of Agriculture (USDA) said in its May 20 Crop Progress report.

In the 18 main corn-growing states, corn planted in the week ended May 19 totaled 71%, up from only 28% planted as of May 12, but still behind the 2008-12 average of 79%.

Plantings during the cool, wet spring experienced across the Corn Belt remained significantly behind last year at the same time, when 95% of the crop was in the ground by May 19, 2012. The corn crop last year was well ahead of average because of a warm, dry spring that ultimately led to a growing season plagued by the worst drought in 50 years.

The week’s increase in corn plantings in top corn-producing Iowa was especially dramatic. The USDA pegged plantings in the previous week ending May 12 at only 15%. By May 19, a total of 71% of the crop was planted in the state, the USDA said.

In Illinois, the second largest corn producer, a similar jump in plantings was reported with 74% of the state’s corn crop in the ground by May 19, up from 17% the previous week, the USDA said.

A total of 19% of the corn crop had emerged as of May 19, well behind the five-year average of 46% and last year’s 73%. Some crop observers have noted that corn planted after May 15 or so runs the risk of reduced yields because key growth stages may coincide with blistering summer heat that may inhibit pollination. Whether that happens this year remains to be seen.

Soybeans, which are typically planted later than corn, were still in the early stages of planting and were not under as much pressure from delays. The USDA said 24% of the crop was planted as of May 19, well behind the 42% planted as the five-year average. In 2012, 71% of the crop was planted as of May 19, the USDA said.

In Iowa, 16% of the crop was planted, far behind the five-year average of 59% for that top soybean-producing state, and up from 1% as of May 12. In Illinois, typically the second largest producing soybean state, a total of 19% of the crop was planted as of May 19, lagging the 35% five-year average but up sharply from no soybeans planted as of May 12.

Only 3% of the crop in the 18 main soybean-growing states was emerged as of May 19, down from 14% as the five-year average, the USDA said.