This is the beginning of one of several new knuckles on a pollarded crape myrtle tree that was pollareded for the first time just this past winter. It was quite a mess of thicket growth that was too congested to bloom well. It is also located in a confined situation where it could not just be groomed, pruned up for clearance, and then just left to develop a larger canopy higher up. Pollarding will both contain it, as well as invigorate healthier growth.
New shoot growth now emerging from the ends of limbs that were pruned back last winter will elongate and eventually bloom through spring and summer. Next winter, after all the colorful autumn foliage has defoliated, the tree will get pruned back to these same knuckles to repeat the process. Stems will get cut back as neatly as possible, leaving no stubs, but such pruning causes knuckles to become slightly more distended as the develop.
Minor shoot growth that develops elsewhere on the mature stems below the developing knuckles should be removed as it appears. It is easy to knock off now, before it gets big enough to need to be pruned off. Knocking it off or ‘peeling’ it off, as drastic as it sounds, is actually better than pruning it off. It removes more of the callus growth that is likely to develop more stem growth later. New growth should be concentrated into the knuckles.
Pollarded crape myrtles bloom later than those that are not pollarded, but they bloom more profusely. They are also more resistant to mildew, and develop better foliar color in autumn.
The picture below shows the same crape myrtle that I got the picture of the single knuckle above from, shortly after it was pollarded. This picture was used another article at:
https://tonytomeo.com/2019/03/16/six-on-saturday-picture-dump/