Q: We have a fruit cocktail tree, bearing plum, peach and nectarine fruit, planted five years ago. It blossomed and had some fruit but the fruit developed a gum-looking disease and eventually fell off. A good number of branches on the tree are infected with this black-looking stuff.

A: I don’t have good news. All of the fruit on your grafted tree are susceptible to a disease called black knot and the affected limbs must be pruned out.

Infection occurs from April through June, especially on the current season’s growth.

Remove all knots and swellings by pruning three to four inches below the knot during the dormant season before April 1.