Answer: Many crabapple varieties have new growth emerging with a reddish coloring and then naturally turning green as the leaves enlarge or in some cases, as the season progresses. In some varieties, the leaves will remain purple for a time and then normally turn green when the heat of summer arrives. Others will stay purple longer. This really depends on the variety you have and sometimes also on the growing conditions.
Keep in mind too that this has been a very difficult drought year and new plants in particular are most susceptible to water stress because they have not yet established their root systems to the fullest. So part of what you are seeing may be related to that.
With regard to the spots, there are a number of foliage problems that can happen with crabapples. I would suggest you take a sample and perhaps a photo of the tree and consult with a professionally trained nursery staff and/or your local Cornell Extension to see if they can diagnose the problem and recommend what to do, if anything. I fyou can tell them the specific variety of crabapple that would also be very helpful, since some varieties are more or less resistant to certain diseases than others.
In many cases a pest or disease problem must be treated in winter or very early spring -- months before the leaves come out. Exactly what to use and how often to use it depends on what the problem is. In the meantime, it is a good idea to regularly clean up and remove the fallen leaves and fruit to minimize the chances for carryover to next year.
Extensive pruning is done in commercial orchards to increase apple production. On an ornamtental crabapple tree, in contrast, pruning needs would be minimal. Any broken or dead branches should be tidied up. Promptly remove any suckers or shoots that pop up from the roots next to the main trunk. These should always be removed as soon as possible.
Good luck with your tree!
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