I have 2 apple trees that are about 5 yrs old. They are about 6 to 7 ft. tall, but the main stem seems to be dead. There are quite a few new branches lower down,near the base and in the middle. Is it ok to cut off that main stem? Not sure what to do.
Unfortunately your photo doesn’t really show the lower part, but it seems like the growth is not from the grafted top part, but rootstock suckers pushing up. Suckers should usually be removed as soon as possible, because they can “suck” some of the energy that should be going into the crown of the tree otherwise. If my assumption is correct (check where the new growth is coming from), you should replace the tree. If the top part - that which was grafted onto the rootstock - is dead, keeping the suckers doesn’t make sense.
The fruit from the rootstock will not be what you expect, because the rootstock was bred and selected for its ability to grow a strong root system and to feed the crown, not for bearing fruit desired for eating or further preparation.