Can you give more information about where you are growing them? Indoors? Outdoors? Container? In ground? Commonest cause of damping off is over-watering but that is less likely in ground.

I'm growing them indoors under lights then will transplant outside

I can't think of any reason to grow them inside. I think you'd have more success sowing them directly outdoors. They do better direct sown anyway as transplanting can encourage bolting. There is little risk of damping off outside and it is cheaper and easier all round.

TOO MUCH WATER., i start them indoors until they are 3/4 inch high then transplant into a PROTECTED row such as i use which is a normal row that is made just below the surface of the ground level. after the plants get 2 or 3 inches, i cut in the surrounding soil to form rows thus bringing the rows to normal levels.

On the far right you can see a finished row of seedlings which are happily growing now that they can withstand the heavy wind and rain that north florida/south georgia recives now in mid- to late march . In the center is a row that i will level then move the center to ground level making a v formation in which i will plant more seedlings. This weekend it will be in the thirtys (march 27-29th 2015) and this type of row will allow me to cover the seedlings by streching heavy plastic over the depression after putting a light mulch such as pest CAREFULLY around the seedlings.

THIS DOES WORK and i get many many beets,giving many away.

The variety I grow is the DETROIT variety which I buy from www.standardseedandfeed.com.