As far as I know, to avoid cross-pollination, you have only three choices:
1) plant each variety at least 250' from each other;
2) make sure that each variety you plant will tassel at a different time (separated by at least 10 days), or
3) plant varieties with similar tasseling times 10 or 15 days apart.

For instance, for 2), you could plant a 62-day variety like Early Sunglow, and a 75-day variety like Butter & Sugar, and a 92-day variety like Country Gentleman all on the same day, but each variety would tassel (and pollinate) at different times, so they would be unlikely to cross with each other.

Or, for 3) you could:
Plant Seneca Horizon (65 days) on May 15, then
Plant Sugar & Gold (67 days) on June 1, then
Plant Spring Snow (65 days) on June 15.

Sue

Great advice but due to colder weather early in the year it might take 3-5 weeks separation in planting date to give two weeks separation in tasseling date. If I plant a second date when the first date is 6 inches tall, tasseling will be separated by about two weeks. A really early planting might take 5 weeks to reach 6 inches tall. In mid summer it's two weeks.

To get really precise, growing degree day calculations are called for.

Thanks belgianpup & fruitnut, never thought of it in that way before.

Unless you are mixing types ( SH2 with other types) or planning to grow out OP varieties for seed, Why are you worrying about cross pollination. Only SH2 has to be isolated. Of couse if you are planting different colors, you do get bicolors, but that does not have a great effect on flavor.

Thank you for your responses, they are very helpful. We have planted Sweet Corn (Early & Often Hybrid) about 3 weeks ago with germ. of 64 days. So if I go ahead in the next couple of weeks and plant the Silver Queen, which has a germ. of 92 days I should be fine right?

Thank you for all your help and insight.
Rhonda

You must plant corn in a patch rather then rows to ensure pollination. I found that out the hard way.