I live in Dallas, Texas and have some crepe myrtle trees that are about to get into power lines (four of them with probably 15-20 shoots of one-inch diameter and approximately 20' tall). My question is, since these trees are already putting on foliage (no blooms), is it too late for pruning back considerably? Will it kill the plants?
Generally, any light trimming should be done just following blooming while hard pruning should wait until late winter/early spring. Here is an article that you may find helpful: https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/best-crepe-myrtle-pruning-time-when-to-prune-crepe-myrtle.htm
Our landscaper cut our crepe myrtle back very short. Is this right? How much should be taken off? They had not been cut back in about eight years and hung very low when blooming.
It sounds like your landscaper was using a method called pollarding. It results in a fuller plant, but one with a weaker branch structure. The tree will recover and look fine, but we normally don't recommend pollarding because of the weakened branch system.
I have a crepe myrtle tree approximately 10' tall, and I have noticed a couple straight line cracks at the base area running up the trunk. I suspect the beetles have laid larva in it because they've gotten other types of trees in my yard. I am afraid I will lose the tree. Does it sound like that could be the problem?
Here is an article or two that you may find helpful: https://www.gardeningknowhow.com/ornamental/trees/crepe-myrtle/crepe-myrtle-tree-problems.htm
https://www.gardeningknowhow.com/plant-problems/pests/insects/japanese-beetles.htm
Is it too late (April 11) to cut back my crepe myrtle?
I would not prune at this time. It will affect blooming. If you don't care about the blooming, then it is ok to prune.
It's green and healthy looking under the bark but no hint of putting on branches. In the past I've trimmed it at the same spot each year which has created a "nub". I know now this is the wrong way to do it, but it seemed to work in the past. Should I cut the "nubs" off or just try to be patient? It looks healthy!
If it is still green and pliable, I would give it some more time. It may be late due to the stress of the move, and additional trimming will only stress it further.
Our crepe myrtle has a lot of new growth but there is also a lot of dead brown blossoms from last year. Should they be cut off?
Yes, you can prune those off. They won't hurt being left on, but they are unsightly.
What's the best way to eliminate fungus from crepe myrtle?
Treat the tree with a fungicide and that should help to clear it up.