Flowering Crab Infected?
My flowering crab tree (approximately 5 years old) is just getting to the point where it flowers beautifully in the spring. However, this year it seems to be losing leaves early, ie, they're turning yellow and fall to the ground. The 1st photo shows the top side of new growth; 2nd photo shows under side of new growth, & 3rd one shows yellow leaves on the ground. Any help you can offer will be most appreciated!
Some crab apple tree cultivars are more susceptible to apple scab than others. Scab causes the symptoms you are seeing - leaves with scab lesions, yellow / brown leaves, early leaf drop. Apple scab is a fungus that is spread by wind and rain, and it is prevalent during wet, humid springs. If a tree is healthy, it is able to survive a certain amount of this leaf loss.
Here is a publication on apple scab http://www.extension.umn.edu/garden/yard-garden/trees-shrubs/managing-apple-scab/ Please look this over and see if it matches the situation you are experiencing with your tree. You can reply to this email with more pictures (always helpful!) and additional questions.
Choosing a resistance variety to plant is the first step and best way to eliminate / reduce the likelihood of scab. Spraying a fungicide for apple scab must begin in early spring before the fungal spores are released (just as tree leaves are opening), so there is nothing you can do right now except rake up and compost the fallen leaves. This should also be done in the fall to minimize the fungal spores next year.