1st plant picture: I would not worry about the brown streaks at the base although I can picture some friends of mine adding Elmer's Washable Clear School Glue to protect the bark some more. I would, for sure, remove the endings that are turning black by pruning below them, say 1/4 to 1/2 an inch below. Cut where the bark is green, not where it looks yellow or black/purple.
2nd picture: I would remove the stem endings of the middle stem, below the affected area. I would also cut the stem ending of the leftmost stem, below the affected area.
3rd: I would not worry about the brown streaks at the base of this one either. There are spots of what could be canker or black spot that developed on the stem. I would cut the two leftmost stems in the circled areas in the edited picture below. The middle stems is a "I am not sure". It may also have to be pruned (see where I wrote "cut???" and drew a line in the picture). Look carefully for my changes; they came out kind of small. Hoipe you can see them.
It is hard to tell if those canker or just a black spot infestation in the injured areas. So just monitor it and take action if the affeted area gets larger. See if it develops more into a true canker or if the black spot fungicides clear that away.
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In addition to using the fungicides, here are a few good housekeeping techniques: Water early in the mornings. Make sure the pot has unclogged holes where the water can exit through. Do not let the pot sit in water for long periods of time. Water the soil, not the leaves (so do not do overhead waterings). Allow the soil to get almost dry before watering; insert a finger into the soil to a depth of 2-3 inches (5 to 7 cm) and see how it feels... wet?, moist? dry?. Checking the soil moisture in this way will make it difficult for the fungi to thrive.
Too much watering can deprive the roots of oxygen, cause root rot, can leech out a lot of nutrients/minerals and can cause the leaves to temporarily turn a different shade of green. If the light greening of the leaves is temporary (reverts back to normal color on its own in a few days) then do nothing. Otherwise, if the leaf veins stay darker than the rest of the leaf, add acidifying compounds (iron sulfate, iron-chelated liquid compounds, garden Sulphur, greensand, etc). Browning and yellowing of leaves can be a plethora of things so see how the shrub does if you only water the soil when the soil feels almost dry to the touch.