Several new shoots on my crabapple have turned brown and wilted. What is the problem?

Fire blight is probably responsible for the wilted shoots on your crabapple.  Fire blight is caused by  the bacterium Erwinia amylovora.  Plants susceptible to fire blight include apple, crabapple, pear, hawthorn, and cotoneaster. 

Symptoms of fire blight appear in spring within a few weeks of bloom.  Succulent, new shoots turn dark brown to black and wilt.  The wilted shoots somewhat resemble the top of a shepherd’s crook or candy cane.  Small droplets of amber-colored bacterial ooze can often be seen on blighted shoots when the weather is warm and humid.  Under favorable environmental conditions, shoot infections may continue to move down the branches and kill large portions of the tree. 

The best way to avoid fire blight is to select crabapple, apple, and pear varieties that are resistant to the disease.  Also, avoid heavy pruning and fertilization that promote excessive shoot growth.  Succulent, rapidly growing shoots are more susceptible to fire blight infections. 

In spring and early summer, periodically inspect susceptible plants for symptoms of fire blight.  Promptly remove infected shoots.  Several precautions should be exercised when pruning in spring and summer.  Never prune during wet weather. Make pruning cuts 8 to 12 inches below diseased areas.  Finally, disinfect pruning tools in a 10 percent bleach solution (1 part household bleach to 9 parts water) or 70 percent alcohol after each cut to prevent spreading the disease.