What’s wrong with my ap­ple tree?

Winnipeg Free Press - Section G - - HOMES - MICHAEL ALLEN

OF­TEN I am asked what the most com­mon prob­lem peo­ple have with trees is. Trees in Man­i­toba are sep­a­rated into two cat­e­gories: conif­er­ous ever­green and de­cid­u­ous broadleaf. Colorado blue spruce tops the conif­er­ous prob­lem list, and fruit trees, ap­ple es­pe­cially, top the broadleaf prob­lem list. This year I am re­ceiv­ing many calls and emails about ap­ple trees. The ques­tions re­late to pre­ma­ture fruit drop­ping, sud­den dy­ing of branches and main trunks, pre­ma­ture leaf drop­ping and pre­ma­ture leaf yel­low­ing. This is­sue is the first part of a two part se­ries on ap­ple tree prob­lems. My next ar­ti­cle will con­tinue with the re­main­der of the com­mon prob­lems. At the start of the spring sea­son, fruit tree buds started to open as usual. Very soon af­ter the buds opened, many of these trees were hit with freez­ing tem­per­a­tures that dam­aged or killed the emerg­ing flow­ers and leaves. To make mat­ters worse, strong winds blew off many de­vel­op­ing healthy fruit. How­ever, if the ap­ple trees were es­tab­lished in a pro­tected lo­ca­tion, their growth was all right. So why are ap­ple trees hav­ing such a hard time this sea­son? There has been a resur­gence of a deadly fun­gal dis­ease that af­fects ap­ple trees in and es­pe­cially out­side the Win­nipeg area. It is called black rot dis­ease. There is no known cure for this dis­ease. Its sci­en­tific name is Botryosphaeria ob­tusa. (I have a de­tailed write up of this dis­ease in my new book, Dr. Tree’s Guide to the Com­mon Dis­eases of Ur­ban Prairie Trees.) This is a com­plex dis­ease show­ing in­con­sis­tent pat­terns of fun­gal in­fec­tion. Some­times pur­ple­brown leaf spots of­ten re­ferred to as “frog-eyes” will show up on the up­per leaf sur­faces. Some­times it may not show up at all. The ap­ple fruit turns mushy and brown and may show a dis­tinc­tive red ring around the blem­ishes. On crabap­ple fruit, this dis­ease can show up as a prom­i­nent black spot cov­er­ing up to half the fruit’s sur­face area. Cu­ri­ously, I have no­ticed the dis­ease symp­toms de­scribed above may or may not show up from year to year on the same tree. There is, how­ever, one fea­ture of this dis­ease con­sis­tent from year to year. The main trunk or stem in smaller trees will have a dis­tinct line sep­a­rat­ing the shrunken dis­eased bark por­tion from the health­ier part of the trunk. The dis­ease por­tion is in the lower trunk closer to the ground. In ma­ture ap­ple trees, the dis­ease kills the twigs and branches first. Twigs and branches will have a dense pat­tern of black spots called py­c­ni­dia lo­cated just un­der the peel­ing thin bark. Py­c­ni­dia will pro­duce mi­cro­scopic spores that will be car­ried by the wind and will in­fect other trees. Of­ten the up­per trunk ar­eas will have a dis­tinct ver­ti­cal crack wide enough to place a 25cent coin in­side. This fea­ture as well as the mass of py­c­ni­dia are shown in my book. Can the tree be saved? Mod­er­ately to se­verely in­fected trees with black rot dis­ease will suc­cumb to the dis­ease. The poorly grow­ing tree will have to be re­moved, es­pe­cially if there are healthy sus­cep­ti­ble ap­ple trees nearby to help stem the spread of the dis­ease. Not sure if your ap­ple tree has this dis­ease, do not hes­i­tate to con­tact me for as­sis­tance.

The red ring on the mushy ap­ple. At top, leaf spot.

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