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SAVE TREES, SAVE LIVES
Začenjamo s serijo prispevkov na temo arborikulture. Arborikultura [lat. arbor –drevo, cultura – gojenje] je gojenje drevja in grmovja na znanstveni osnovi. Naši strokovnjaki odgovarjajo na najpogostejša vprašanja o drevju v urbanem okolju.
Bolezen na listih okrasne hruške (Pyrus calleryana 'Chanticleer') – kako ukrepati?
Vprašanje: oglašam se z vprašanjem o (domnevno) glivični bolezni na listih okrasne hruške ( Pyrus calleryana 'Chanticleer'), ki je bila posajena konec leta 2018, na igrišču pred eno od ljubljanskih osnovnih šol. Zanima me, ali mi lahko na podlagi priloženih fotografij, te so bile posnete lani jeseni, poveste za katero bolezen gre in če je ta kakorkoli problematična za normalen razvoj drevesa? Zanima me tudi, ali je prisotnost takšnega obolenja lahko problematična, da se je pojavila na odprti površini, kjer se zadržujejo otroci? V kolikor ste mnenja, da bi bilo bolezen potrebno zatirati, kakšni ukrepe bi priporočili?
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Odgovor: hruševe liste je okužila gliva Gymnosporangium sabinae (Dicks.) G. Winter 1884, ki povzroča hruševo rjo. Bolezen spoznamo po oranžnih pegah na hruševih listih in trosiščih (imenujemo jih eciji, spomladanska trosišča na haplontskem gostitelju) ki jih gliva oblikuje jeseni.
Opazimo jih kot drobne, rjave izbokline na oranžnih pegah (dobro so vidni na poslanih slikah). Okuženi listi običajno prej odpadejo kot zdravi in ob vsakoletnih in močnih okužbah drevo slabše prirašča in hira. Jakost okužbe je odvisna od dveh dejavnikov: od vlažnega vremena v času okužbe listov in od prisotnosti dikariontskega gostitelja rje, na katerem nastajajo trosi, ki okužujejo hruševe liste. Dikariontski gostitelji so pri hruševi rji brini iz podroda Sabina (luskasto brinje), to pa so predvsem vrste Juniperus sabina (smrdljivi brin, ki raste pri nas, vendar je zelo redek) ter okrasni tujerodni brini, predvsem kitajski brin (Juniperus chinensis) in virginijski brin (J. virginiana).
Predvsem kitajski brin gojijo kot izredno uporabno okrasno grmičevje v njegovih številnih križancih in oblikah (kultivarjih), npr. Juniperus x pfitzeriana in drugi. Spomladi (konec aprila in v začetku maja) se po deževju na skorji vejic in debelejših vej brinov pojavijo zimska trosišča glive (teliji), ki izgledajo kot nekaj cm dolgi, sluzasti jezički rjasto rjave barve. Tu se oblikujejo trosi, ki okužijo liste hrušk, ki v tistem času brstijo. Trosi so zelo kratkoživi in lahko okužijo hruševe liste le v bližini (npr. nekaj 100 m daleč) od okuženega brina.
Najučinkovitejši način preprečevanja bolezni je odstranitev okuženih okrasnih brinov iz okolice hrušk, ali odstranjevanje okuženih vej na brinih. Okužbe s to glivo na brinih spoznamo po odebelitvah na vejah, na katerih se spomladi oblikujejo rjasto rjava, sluzasta trosišča. Okužene veje odstranimo. Če so brini stari, so lahko okužbe na njihovih vejah množične in je treba odstraniti celotno rastlino. Rja na brinu ne prizadene brin močno, šele po mnogih letih nekatere okužene veje odmrejo. Seveda je mogoče obvarovati hruško pred okužbo s hruševo rjo s škropljenjem s fungicidi v času okužb spomladi, vendar zaradi urbanega okolja uporaba pesticidov nikakor ni ustrezna.
Pripenjam sliko telijev (zimskih trosišč) hruševe rje na vejici kitajskega brina.
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Sestavil
prof. dr. Dušan Jurc
V Ljubljani, 14.3.2020
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