The Plague of Pears

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The Plague of Pears Invasive Species Workshop Mark Grueber, Urban & Community Forester Missouri Department of Conservation [email protected]

description

Presentation by an MDC forester on the concerns of callery pears.

Transcript of The Plague of Pears

Page 1: The Plague of Pears

The Plague of PearsInvasive Species Workshop

Mark Grueber, Urban & Community Forester

Missouri Department of Conservation

[email protected]

Page 2: The Plague of Pears

Who is this Nutball?

…and why is he talking to us about pear trees?

I am partially to blame for this mess!

I am not a researcher nor have I actively managed Callery Pear

I am old and crusty and pretend to know what I’m talking about.

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Callery Pear – The History

Pyrus calleryana a.k.a. ‘Bradford’ Pear

An early introduction (early 1900s) to the U.S., initially to improve disease resistance of common (fruiting) pear

The ‘Bradford’ cultivar was widely planted as an ornamental in the 1950s

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Callery Pear – The History Continues

The formal, dense canopy and upright shape made them a favorite for planting in urban areas

VERY popular with landscape architects

Extraordinarily easy to grow in the nursery, transplant, and survive the cramped, poor conditions in the urban landscape

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Callery Pear – The History Continues

“…little did I realize that this cultivar would literally inhabit almost every city and town to some degree or another; the tree has reached epidemic proportions and is over-planted similar to Green Ash, Silver Maple and Siberian Elm;“‘Bradford’ is beautiful(?) but not a panacea for urban planting”- Michael Dirr; Manual of Woody Landscape Plants

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Callery Pear – The Bloom Fades

Arborists, urban foresters, landscape professionals get tired of cleaning up ‘Bradford’ pears after storms

People complain of the smell of rotting flesh, dog feces, etc. and realize that pear flowers stink!

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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 ChinaIndividual cultivars considered self-sterile are able to cross pollinate with different cultivars and produce fruit with viable seedShoots from rootstock developed with varying genetic makeup are able to cross pollinate with the original tree

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The Plague of Pears

Uh oh…the first escaped plants are found in the mid-1960’s in eastern Arkansas and Talbot County MarylandIn 1994, ‘Bradford’ and its cultivars are found to have little invasive potentialTen years later, 26 states have P. calleryana in natural areasI recall reading about issues with pear in the east in the late 90s; heard about problems in KC in the early 2000s; noticed a local explosion about 4 years ago

Figure 3. The recommended planting range of the ‘Bradford’Callery pear (shown in gray) in the United States. The “x” denotes the 26 states in which wild Pyrus calleryana has been collected or observed. This consists of the 23 states found by Vincent (2005) and the states of Virginia (M. Becus, voucher #103031 and #10306b, CINC), Oklahoma (Taylor et al. 1996), and Connecticut (L.J. Mehrhoff, #124627 CONN). Source: Adapted from Fact Sheet ST-537 from the University of Florida, Institute of Food and Agricultural Sciences (November 1993).

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Callery Pear - Identification

Foliage – glossy, oval leaves with fine toothed margins; alternate leaf arrangement; reddish-purple in fallFlowers – very early bloom (mid to late March); malodorous; white with 5 petals; bloom usually before leaf emergenceServiceberry, plums and crabapples have similar bloom time; serviceberry has thinner petals that are more widely spaced; native plums have stamens that are longer than the petals; apple and crabapple have a slight pink colorTrees have upright, pyramidal shape and typically have thorns

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Callery Pear – The Biology

Pears have many traits that contribute to its ability to spread into many environmentsThese biological are found in the native range of the species and enhance its ability spread and persist 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

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Callery Pear – Reasons for the Spread

Flowers are highly attractive to insect pollinators, including generalist honeybees (Apismellifera L.), bumblebees (Bombus terrestris L.), other introduced bees, and hoverflies (Syrphidae)Self-incompatibility promotes outcross fertilization and thereby maximizes reproductive output and genetic variationFruits are consumed and the seeds dispersed in late fall by a variety of animals, such as European starlings and American robins

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Callery Pear – The Impacts

Single wild tree can spread quickly by seed and vegetative meansTendency to form dense thickets within several years crowds out native species in open woodland, old field, prairie, glade and savanna habitatsProbably has greatest impact on the establishment of late and mid-successional species in disturbed sites; significant problems have occurred on newly restored wet prairiesConcern with invasion into utility rights-of-way

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Callery Pear - Control

Small trees can be removed by hand in areas of light infestation in moist soilsFor heavier infestations of small trees, foliar applications of 2-5% of glyphosate or triclopyr in mid to late summer have been effectiveMedium to large trees should be cut down and (immediately) stump treated with glyphosate or triclopyrat 25 to 50% solutionBasal bark treatment can be used for trees up to 6” in diameter; 20% triclopyr solution in a 12” band around the entire circumference; late winter/early spring or mid-summer is most successfulMature trees can be girdled during the spring or summer; 6” above the ground; sprout treatment will be necessary

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Callery Pear - Control Strategies

Removal of wild Callerypear is a treatment of the symptomRemoval and replacement programs• Lake Saint Louis• Columbia

Educating the public about alternatives• Serviceberry• Flowering dogwood• Eastern redbud• Yellowwood• Blackhaw viburnum

Pyrus calleryana Removal at City Hall

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.

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Sources and Additional Resources

Manual of Woody Landscape Plants; Michael A. Dirr, First, Second & Fifth Editions

The Beginning of a New Invasive Plant: A History of the Ornamental Callery Pear in the United States; BioScience, December 2007

Callery Pear – Invasive Species; Missouri Department of Conservation, 4/2012