Memorial Day weekend rains, plus prospects for more from North-bound Tropical Storm Alberto, threaten to further delay corn planting's wrap-up in the Northeast. As of Memorial Day, USDA's National Agriculture Statistics Service reported all Northeast states, except Delaware, were significantly behind on corn planting. States with the largest corn acreage were farthest behind.

• Maryland. 73%, down 10% from the five-year average.

• New England. 70% complete.

• New Jersey. 54%, down 8% from the five-year average.

• New York. 48%, down 13% from the average.

• Pennsylvania. 59%, still 19% off that average.

What to plant now?
If you don't have all your corn in the ground and growing now, your optimum planting date is long past. So now what — swap longer season hybrids for shorter season ones?

Maybe, maybe not. "Hybrids have an ability to adjust the amount of time in vegetative and reproductive development depending on the hybrid's relative maturity, says Bob Kratochvil, Extension agronomist at University of Maryland.

Research at Purdue University and Ohio State University assessed hybrid maturity responses to corn planting in early May, mid-to-late May and early June. Here are three key findings:

• As planting date was delayed, the period between planting and silking shortened. Longer season hybrids' vegetative period shortened more than shorter season hybrids.

• Days between silk and physiological maturity lengthened as hybrid maturity lengthened. Days from silk to maturity averaged 63, 66, and 68 days, respectively, for early, mid and late planting dates.

• The reduction in time spent in vegetative growth compensated for the increased time spent in reproductive growth. In a nutshell, vegetative growth was shortened up to 14 days for the latest planting date while the reproductive growth was lengthened up to 5 days.

Hybrids can compensate by shortening the time necessary to reach silk. "If wet conditions continue, you'll eventually have to consider how much growing season you'll have before your average date of first frost," adds Kratochvil.

Gauge your GDDs
A corn hybrid with a 90- to 95-day relative maturity requires 1,600 to 1,825 growing degree days to reach black layer, adds Dwane Miller, Penn State Extension agronomist. A 111- to 115-day hybrid which requires 2,500 to 2,724 GDD's. Keep in mind, as noted above, that hybrids may reduce their GDD requirements by 100 to 150 GDD's in late planting situations.

Bottom line: Your corn should easily make physiological maturity by that date. Regardless of whether you farm in central Maryland, northern New England or any place in between, you'll need an adequate number of GDDs to easily get corn hybrids to black layer. By June 1, you've already lost a considerable number of those potential GDDs.