Yes, you will need to net any blooms/plants that you want to isolate. They say they can cross pollinate up to a mile away but I would feel safe with a couple hundred yards between plants. So be sure to bag whole plants or branches if you are growing several varieties in the same area (yard). Some varieties cross easier and that is info I don't have but the more seasoned growers here can give you some guidance there.
Bruce

PS: Just in case, I want you to understand that crosses this year will only affect the seeds in this year's crops. As long as you are using pure seed this year, your peppers will grow true no matter if crossed or not. It is the seeds from those peppers that may be hybrids.
Bruce

What Bruce said and here is the chart from the FAQ on the site that explains crosses.

Here is a link that might be useful: Chart

Mark, thank you for this link.

Caelian

can anyone share some links for bagging, or other methods to isolate plants to ensure no cross pollination ?

thismembername: Yes, click on the link below and then scroll down in the thread to the June 4, 2012 posting by me.
Bruce

Here is a link that might be useful: Bagging Peppers

thanks bruce, i also sent you an email regarding another thread.

Thanks fellas! Hopefully I'm using pure seed this year!!!!!

There is a lot to be said for letting them pollinate as they will, or at least keeping several plants of the same variety next to each other and letting them cross pollinate.

It doesn't happen as quickly with peppers, tomatoes, and other plants that easily self pollinate, but there is something known as Inbreeding Depression, where plants grown from lines without enough external fertilization will slowly degrade and become less and less productive.

The older farmers would talk about crops wearing out, thats exactly what they were talking about. Corn is especially bad at that, needing a fairly large number of plants to keep the line healthy (upwards of 200 individual stalks), otherwise you'll see productivity loss within a half dozen generations or so.

Not sure how long peppers can go before it becomes a problem though.