Most lenses flare easily in IR as the lens coatings are not designed for handling out-of-visible light. You just have to work around the problem, or use it for pictorial effects.
Do note that digital IR tends to come out quite "flat" and dull, entirely unlike the (false) impression we got from the old Kodak IR film. While the Kodak "IR" with blocked shadows and glowing highlights was incorrect, and digital IR is more true, we still need to post-process to give a more pleasant rendition of the scene.
Using an R72 filter the sky will rarely go entirely black in IR if you shoot near populated areas. This is due to aerial dust and contamination. Thus balance the gradation against vegetation instead.