Diseases Of WaxM In Florida Landscapes

response to BY Dr. E. L. Barnard Forest Pathologist , and at­ Division ofForestry, tractive evergreen foliage. The popu­ FDACS larity of -myrtle as an ornamental Wax-myrtle or southern bay­ in Florida is further enhanced by its berry ( cerifera L.) is a native status, low maintenance or small native to the southeast­ requirements, wildlife food value, and ern coastal plain of the United States. statewide availability. Its natural range extends from southern Generally, wax-myrtle is not seri­ New Jersey to the Florida Keys and ously affected by infectious diseases, westward into southeastern Oklahoma, another feature which adds to its desir­ EastTexas,andCentralAmerica Wax- , ability as anornamental. In recent years, myrtle is also endemic t-0 Bermuda and however, two relatively obscure and the West Indies. The , bark, , potentially serious diseases have been branches,and waxy ofwax-myrtle diagnosed with increasing frequency on have been used for various medicinal wax-myrtle in Florida landscapes. This purposes, and the wax from its berries is could reflect an upsurge in disease oc­ still used to make fragrant bayberry ,..· currence or simply be a natural result of candles, as well as soap and shoe polish the increased utilization of wax-myrtle • in some localities. as an ornamental. In either case, recog­ · ··~ Wax-myrtle is adaptable to a vari­ nition by arborists and other landscape , . ety ofsite conditions and is increasingly professionals is a first step toward in­ popular as an ornamental due to its rapid growth, favorable creased understanding and eventually better plant health care.

3 Fusarium wilt.Wax-myrtleexhibitingagen­ in natural settings as well as in urban land­ eral loss of vigor, stunted, curled, wilting, and scapes in southern Florida. Infected plants may ap­ off-color foliage, and/or death of branches or pear unthrifty, but healthy appearing plants are in- ~ entire stems are commonly infected by the vas­ fected as well. The branch stubs and associated callus Wlr cular wilt fungus, Fusarium oxysporum. Al­ tissues of infected plants often display adark brown ... .'. ·,;, though laboratory isolation and identification of to red-brown or coffee-colored staining due to the . · ..· ' the fungus is required for diagnostic confirma­ apparently profuse "bleeding" of xylem sap at these ' .. -. tion of the disease, visual diagnostic support is foci. At certain times, the fungus produces distinc­ often supplied by adistinctive pale to dark brown tive "dusty", red-brown to broWn beard-like growths staining or discoloration of the xylem (wood) in at the branch stubs. These growths are the fruiting bodies of !he fungus' asexual stage (Ptychogaster infected branches and stems (fig. J). Sometimes, cubensis), and the "powder" or "dust'.' is a profusion _·., · depending upon stage ofdevelopment, lighting, etc., offungus spores; a helpful diagnostic feature. ·' :,,_ this vascular staining displays anotably purplish hue _Internally, Inonotus rickii causes a distinctive (perhaps related to pigmentation ofthe fungus itself). spongy, yellow-brown to red-brown decay of the To date, confinned reports of the disease are all from central xylem (he~) tissues ofinfected wax-myrtles central to southern Florida, with anotable number of (fig. 2). This decay is often flecked with distinct reports concentrated near Tampa Bay. streaks of white (mycelium of the fungus itself) and Fusarium oxysporum is a soilbome fungus and is bordered by a dark purplish-brown zone of solid, presumably enters wax-myrtles by direct penetra­ but stained xylem tissue (possibly evidence tion of roots or through wounds resulting from . of strong compartmentalization). Extensive decay may con- transplanting or landscape maintenance operations. · ·: .. tribute to ageneral deeline in plant vigor ~ ... Feeding injuries caused by certain plant parasitic .. and renders infected stems vulnerable to breakage. nematodes may also be important points of entryfor Infections of lnonotus the fungus. Once inside asusceptible host, the fungus rickii presumably result from airborne spores which at enters the xylem and colonizes the plant's vascular initiate infection branch system. This results in restricted water flow, and the stubs or stem injuries. Accordingly, prevention in e :: urban landscapes is based on sound arboricultural - eventual demise of the infected plant. · ·•.··~ practices. Avoid planting infected Because of the soilborne nature of the wax.­ plants, minimize · myrtle wilt fungus, disease management is based on stem/branch .injuries, and conduct pruning opera­ tions carefully. Do not prune common sense and good horticultural practices. Rec­ during periods when sporulating structures (e.g., ognize the risks ofpathogen-infested soils (e.g., soils the beard-like ­ where plants have succumbed to the disease), mW­ ing bodies,) are known to occur. mize injuries to landscape plants, practice good Aword ofcaution. Apparently, it is not uncom­ mon to extract wax-myrtle sanitation (i.e., removal of infected plants/infested from the wild for market soils) when replacing diseased plants, and avoid the and landscape purposes. Accordingly, since both movement or use of infected plants and pathogen­ Fusarium wilt and lnonotus heartrot occur in natural infested soils. Soil fumigation may be useful in stands, extreme caution must be exercised during certain situations, im.d the possibility ofdisease resis­ such operations. Digging and marketing infected plants is asure-fire way to spread disease and worsen · . 1 tant wax-myrtle varieties or iIJ. the future should not be dismissed. the threats represented by the diseases. "An ounce of Inonotus heartrot. The fungus, lnonotus rickii, prevention is worth a pound of cure". causes a severe heartrot in the stems of wax-myrtle. Infections have been observed in abundance on •

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