The document discusses the invasive nature of Callery pear trees in North America. It begins with a history of how the trees were introduced from China in the early 1900s and became widely popular ornamental trees. However, they have since escaped cultivation and spread aggressively through seed dispersal and vegetative means, forming dense thickets that crowd out native species. Controlling and removing established Callery pears requires diligence, as they are very tolerant of different environments. Public education on alternatives to planting Callery pears is important, as is replacing existing trees with native species.

1. The Plague of Pears
Invasive Species Workshop
Mark Grueber, Urban & Community Forester
Missouri Department of Conservation
mark.grueber@mdc.mo.gov

2. 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.

3. 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

5. 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

6. 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

7. 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!

8. 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

9. The Plague of Pears
Uh oh…the first escaped
plants are found in the mid-
1960’s in eastern Arkansas
and Talbot County Maryland
In 1994, ‘Bradford’ and its
cultivars are found to have
little invasive potential
Ten years later, 26 states
have 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 been
I recall reading about issues collected or observed. This consists of the 23 states found by
Vincent (2005) and the states of Virginia (M. Becus, voucher
with 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 of
problems in KC in the early Florida, Institute of Food and Agricultural Sciences (November
1993).
2000s; noticed a local
explosion about 4 years ago

10. Callery Pear - Identification
Foliage – glossy, oval leaves with
fine toothed margins; alternate
leaf arrangement; reddish-purple
in fall
Flowers – very early bloom (mid
to late March); malodorous;
white with 5 petals; bloom
usually before leaf emergence
Serviceberry, 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 color
Trees have upright, pyramidal
shape and typically have thorns

11. Callery Pear – The Biology
Pears have many traits that
contribute to its ability to spread
into many environments
These 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

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

13. Callery Pear – The Impacts
Single wild tree can spread
quickly by seed and vegetative
means
Tendency to form dense thickets
within several years crowds out
native species in open woodland,
old field, prairie, glade and
savanna habitats
Probably has greatest impact on
the establishment of late and
mid-successional species in
disturbed sites; significant
problems have occurred on newly
restored wet prairies
Concern with invasion into utility
rights-of-way

14. Callery Pear - Control
Small trees can be removed by hand
in areas of light infestation in moist
soils
For heavier infestations of small
trees, foliar applications of 2-5% of
glyphosate or triclopyr in mid to late
summer have been effective
Medium to large trees should be cut
down and (immediately) stump
treated with glyphosate or triclopyr
at 25 to 50% solution
Basal 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 successful
Mature trees can be girdled during
the spring or summer; 6” above the
ground; sprout treatment will be
necessary

15. Callery Pear - Control Strategies
Removal of wild Callery
pear is a treatment of the
symptom
Removal and replacement
programs
• Lake Saint Louis
• Columbia
Educating the public about
alternatives
• 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.

16. 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