The Plague of Pears Invasive Species WorkshopMark Grueber, Urban & Community Forester Missouri Department of Conservation email@example.com
Who is this Nutball?…and why is he talkingto us about pear trees?I am partially to blamefor this mess!I am not a researchernor have I activelymanaged Callery PearI am old and crusty andpretend to know whatI’m talking about.
Callery Pear – The HistoryPyrus calleryana a.k.a.‘Bradford’ PearAn early introduction(early 1900s) to theU.S., initially to improvedisease resistance ofcommon (fruiting) pearThe ‘Bradford’ cultivarwas widely planted asan ornamental in the1950s
Callery Pear – The History ContinuesThe formal, dense canopyand upright shape madethem a favorite forplanting in urban areasVERY popular withlandscape architectsExtraordinarily easy togrow in thenursery, transplant, andsurvive thecramped, poor conditionsin the urban landscape
Callery Pear – The History Continues“…little did I realize that thiscultivar would literallyinhabit almost every cityand town to some degree oranother; the tree hasreached epidemicproportions and is over-planted similar to GreenAsh, Silver Maple andSiberian Elm;“‘Bradford’ is beautiful(?)but not a panacea for urbanplanting”- Michael Dirr; Manual ofWoody Landscape Plants
Callery Pear – The Bloom FadesArborists, urbanforesters, landscapeprofessionals get tiredof cleaning up‘Bradford’ pears afterstormsPeople complain of thesmell of rotting flesh,dog feces, etc. andrealize that pear flowersstink!
Callery Pear – The “Improved Cultivars” The nursery industry takes advantage of the market opportunity and creates “improved varieties” by the gazillions, e.g. Aristocrat, Autumn Blaze, Capital, Cleveland Select, Redspire, Trinity, etc. – many of these new selections come from P. calleryana from different areas of China Individual cultivars considered self-sterile are able to cross pollinate with different cultivars and produce fruit with viable seed Shoots from rootstock developed with varying genetic makeup are able to cross pollinate with the original tree
The Plague of PearsUh oh…the first escapedplants are found in the mid-1960’s in eastern Arkansasand Talbot County MarylandIn 1994, ‘Bradford’ and itscultivars are found to havelittle invasive potentialTen years later, 26 stateshave P. calleryana in natural Figure 3. The recommended planting range of the ‘Bradford’areas Callery pear (shown in gray) in the United States. The “x” denotes the 26 states in which wild Pyrus calleryana has beenI recall reading about issues collected or observed. This consists of the 23 states found by Vincent (2005) and the states of Virginia (M. Becus, voucherwith pear in the east in the #103031 and #10306b, CINC), Oklahoma (Taylor et al. 1996), and Connecticut (L.J. Mehrhoff, #124627 CONN). Source:late 90s; heard about Adapted from Fact Sheet ST-537 from the University ofproblems in KC in the early Florida, Institute of Food and Agricultural Sciences (November 1993).2000s; noticed a localexplosion about 4 years ago
Callery Pear - IdentificationFoliage – glossy, oval leaves withfine toothed margins; alternateleaf arrangement; reddish-purplein fallFlowers – very early bloom (midto late March); malodorous;white with 5 petals; bloomusually before leaf emergenceServiceberry, plums andcrabapples have similar bloomtime; serviceberry has thinnerpetals that are more widelyspaced; native plums havestamens that are longer than thepetals; apple and crabapple havea slight pink colorTrees have upright, pyramidalshape and typically have thorns
Callery Pear – The BiologyPears have many traits thatcontribute to its ability to spreadinto many environmentsThese biological are found in thenative range of the species andenhance its ability spread andpersist in new locations • Reproduction begins early – usually around 3 years of age • Leafs out early and holds leaves late into fall • Produces abundant flowers which can result in up to 10 seeds per flower; usually around 2 to 6 • Fruit is small, round, olive-brown and appear from May to July • Callery pear is extremely tolerant of a wide range of soil conditions, drought, heat and pollution • Prefers full sun but tolerates partial shade
Callery Pear – Reasons for the SpreadFlowers are highly attractive toinsect pollinators, includinggeneralist honeybees (Apismellifera L.), bumblebees(Bombus terrestris L.), otherintroduced bees, and hoverflies(Syrphidae)Self-incompatibility promotesoutcross fertilization and therebymaximizes reproductive outputand genetic variationFruits are consumed and theseeds dispersed in late fall by avariety of animals, such asEuropean starlings and Americanrobins
Callery Pear – The ImpactsSingle wild tree can spreadquickly by seed and vegetativemeansTendency to form dense thicketswithin several years crowds outnative species in open woodland,old field, prairie, glade andsavanna habitatsProbably has greatest impact onthe establishment of late andmid-successional species indisturbed sites; significantproblems have occurred on newlyrestored wet prairiesConcern with invasion into utilityrights-of-way
Callery Pear - ControlSmall trees can be removed by handin areas of light infestation in moistsoilsFor heavier infestations of smalltrees, foliar applications of 2-5% ofglyphosate or triclopyr in mid to latesummer have been effectiveMedium to large trees should be cutdown and (immediately) stumptreated with glyphosate or triclopyrat 25 to 50% solutionBasal bark treatment can be used fortrees up to 6” in diameter; 20%triclopyr solution in a 12” bandaround the entire circumference; latewinter/early spring or mid-summer ismost successfulMature trees can be girdled duringthe spring or summer; 6” above theground; sprout treatment will benecessary
Callery Pear - Control StrategiesRemoval of wild Callerypear is a treatment of thesymptomRemoval and replacementprograms• Lake Saint Louis• ColumbiaEducating the public aboutalternatives• Serviceberry• Flowering dogwood• Eastern redbud Pyrus calleryana Removal at City Hall• Yellowwood• Blackhaw viburnum The City of Lake Saint Louis received a grant through the Missouri Department of Conservation to remove and replace the (18) callery pears along the driveway.
Sources and Additional ResourcesManual of WoodyLandscape Plants; MichaelA. Dirr, First, Second & FifthEditionsThe Beginning of a NewInvasive Plant: A History ofthe Ornamental Callery Pearin the United States;BioScience, December 2007Callery Pear – InvasiveSpecies; MissouriDepartment ofConservation, 4/2012