Leaves Turning Yellow on a Flowering Crab?

Q: I have a flowering crab and its leaves are turning yellow. A tree guy told me it's fungus but he's an amateur so I'm not sure. I'm looking for a way to treat it naturally. Is that possible? Thanks!

A: Without seeing your tree, my guess would be that your tree is suffering from a typical case of Apple Scab. This is a common affliction of apple trees, especially in Eastern parts of the U.S. where warm rainy weather prevails. Symptoms are yellow leaves with brown spots followed sometimes by heavy early defoliation and scabby or "corky" fruit. It is probably too late to do anything about it at this stage of the season, but the fungus over-winters in leaf litter, so make sure to collect fruit and rake up fallen leaves this fall. Prune suckers and branches in the crown to improve air circulation so leaves can dry quickly, as well as your usual annual pruning in late winter or early spring (toss out waste). Spray your tree in the spring with liquid sulfur once flower buds show pink. Repeat 10 days later and when moist, calm weather lingers.