Question
My ornamental crabapple tree leaves have a scary looking infestation.  First there are dark brown spots that don't become holes.  Then they appear to explode out like, (forgive the drama) an alien in the horror movie.  They leave many tall curved spikes that curve up and out from the spot site, looking kind of like some kind of insect.  There are several per leaf, but I didn't see any harm to the fruit of the tree.  What is this and how do I cure it?  

Answer
sounds like it could be crab apple scab. there are thousands of plant pest/disease problems out there, so w/out seeing it i can't be sure.
to be certain snip off a small section of a branch w/marks on the leaves, seal it in a plastic bag, and take it to your local garden center for ID. if they aren't sure what it is go to another garden center that does. it's not wise to just spray when you see pest on plants. horticulture people are learning that our best hope to control most pest is by utilizing beneficial organic products and let nature do its' work. integrated pest management(IPM) is the big buzz-word in pest control in the new millenium. 1st you have to ID the problem pest so you know how to best get rid of it. chemical pesticides are necessary sometimes, but sometimes they do more harm than good. usually it is not good to indiscriminately spray all pest infestations. many insects(over 99%) are actually beneficial. by indiscriminately spraying chemicals we often kill off the natural predators of plant diseases and other pest. ID the problem pest 1st. get to a local garden center/nursery and quiz them on a solution to your problem.  buy your products from them and they should be more than happy to help you. i'm in southern NJ.

hope this helps.
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good luck
rick