Here is a listing of links from USDA’s Risk Management Agency that pertain to prevented planting. I hope most of you folks never need these; but I know many of you might need them this year! Thanks to Desiree King from RMA for passing these along (and for all of here help in this matter).
Here is our Prevented Planting Fact Sheet which explains the options a producer has when they are prevented from planting (including the option to plant a cover crop): http://www.rma.usda.gov/pubs/rme/ppflood.pdf
Here are our 2011 Basic Provisions (see section 17 regarding prevented planting rules-specifically Section 17(f)(5)) which state that a cover crop may be planted on PP acreage within or prior to the late planting period, but a cover crop may not be hayed, grazed or otherwise harvested within or prior to the late planting period. http://www.rma.usda.gov/policies/2011/11-br.pdf
Finally, here is a link to our Prevented Planting Loss Adjustment Standards Handbook. Section 5 (c) has a section on cover crops and prevented planting, which explains that they may not be hayed or grazed until November 1st and may not be otherwise harvested at any time. http://www.rma.usda.gov/handbooks/25000/2011/11_25370.pdf
All of these documents are available on the RMA website (http://www.rma.usda.gov/)
Here are links that give options for what to plant for cover crops. Summer annual grasses for cover crops for prevented planting acres and Prevented Planting Row Crop Acres – Which cover crops can help?