Answer: You may be dealing with three problems with your crabapple. The frothy mass could have been caused by spittle bugs. These tiny leafhopper looking insects suck the juices out of plants. They disguise themselves from predators by manufacturing a covering of what looks like spit. If you hose it off the insects stay but the froth washes away, and the spittle bugs just manufacture more spit.
You may also be dealing with red spider mites. These critters leave a blood-red stain when squished, because of the red tint their bodies have. Spider mites can also do some damage to plants late in the season.
Sowbugs feed on decaying organic matter. Finding these in a tree wound is not unusual, but does indicate there's some dead material there. You might be able to correct the condition by scraping out the wound and dead material until you find sound wood. A clean wound is easy for a tree to callous over.
If the wound is near the soil surface, it may have been caused by a weed whacker or lawn mower getting too close. To protect your tree, remove the grass and weeds from beneath the canopy and use a mulch material over the soil surface. This will help suppress weeds and slow water evaporation. It will also help avoid future injuries.
Hope your crabapple grows strong and healthy!
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