Stop the Spread!

How’s this for a creepy sci-fi movie? Humans transport aliens to Earth without worry because we are sure they cannot reproduce here. Thirty years later a quiet, spectacled scientist discovers that the aliens are spreading. Indeed, alien offspring multiply and escape to our farms and parks, crowding our youngsters that are desperately trying to hang on… you get the point.

Now, replace the word alien with ornamental pears and you’ll see this is not sci-fi but a real-life dilemma. Ornamental pears are spreading in Missouri and causing quite a stir with landowners.

Ornamental pears were introduced to the United States in the early 1960s and came from China. All ornamental pears originate from Pyrus calleryana, or callery pear, commonly referred to as Bradford Pear. Bradford is indeed the oldest cultivar, or kind, of ornamental pear. Newer cultivars include Chanticleer, Aristocrat and Cleveland Select, to name a few. Ornamental pears were originally very popular trees due to their prolific spring flowers, dark glossy leaves and ability to thrive in almost any kind of soil—and because people thought they were sterile and therefore had no messy fruits to contend with.

The first major downfall of ornamental pears came 15–20 years after the initial trees were planted. At that point, many unsuspecting homeowners found out that the branches and trunks of pears split in storms. Many reading this article can relate to waking up after a windy night to their prized yard tree ripped down the middle and lying across their driveway. Also, ornamental pears are more susceptible to a fungal disease called fire blight than was hoped when they were first introduced.

However, it has not been until the last few years that people have been noticing the ornamental pears we thought could not spread … are. And, they are doing so quite prolifically. In fact, 26 states have reported wild callery pears spreading in the past decade. How could this have happened?

There are two causes. One is due to the fact that ornamental pears have been overplanted in our communities. Although each different kind of callery pear cannot reproduce by itself, it turns out that when these many types of pear are all planted close together (like they are in our towns) they can crosspollinate and produce fruits. The other method of ornamental pears reproducing is if the sprouts that sometimes grow from the base of pears are not pruned they can flower and crossbreed with the flowers of the tree itself. These small fruits are eaten by birds and are then scattered along fences and roadways, pastures, abandoned fields, natural areas and under power lines. Wild trees then sprout from these fruits and begin reproducing quite quickly. In fact, wild callery pear trees start producing flowers and spreading themselves after just three years.

Wrangling the Wild Callery

Some of the characteristics of wild callery pears are similar to the callery pears they originate from. They grow quickly, flower prolifically and will tolerate a wide variety of soils, character traits typical of an invasive weed. Moreover, some of the new wild trees are bringing back characteristics of the original trees from China like very large, stout thorns, making a field filled with wild callery pears difficult to clear.

Wild callery pear trees can have a significant economic impact in that ridding them from pastures, disturbed areas, under power lines and in natural areas can be costly. They can have a sizable environmental impact as well as crowding out and shading our native plants. These trees produce small fruits inedible to humans, not large juicy fruits like we think of at the store.

To pick out wild callery pears, look for their tight crowns and white flowers in the spring, especially along roadsides where trees have not been planted. Ornamental pears are one of the first trees to leaf out in the spring and retain their leaves until late into autumn. They do prefer full sun so will be found most often in open areas. Late in the fall, their red/purple leaves can be noticed in fields and disturbed areas. Once you key in on their characteristics, it’s amazing how many wild callery pears you will spot.

One Missouri community has taken this issue by the thorns. In 2007, Columbia’s Parks and Recreation Department was successful in obtaining a TRIM grant from the Missouri Department of Conservation to help fund a campaign aimed at informing the public about the invasive quality of ornamental pears. Coined STOP THE SPREAD! the city’s program has been very successful. For instance, volunteers have been removing wild callery pears from the city’s natural areas. A city park has been planted with 10 kinds of native, flowering trees to showcase what could be planted as alternatives to ornamental pears. You can visit their website at http://www.como.gov/ParksandRec/Parks_and_Facilities/stopthespread.php to view trees to plant as alternatives to ornamental pears—and to find brochures, articles, ads and more that the city created to help spread the word.

Brett O’Brien, natural resource supervisor with Columbia’s Parks and Recreation Department, understands that people look to city parks and other public areas for examples of what trees to plant. He is working to reduce the number of ornamental pears in Columbia’s park system and replace them with flowering trees that are not invasive and have lower maintenance needs than pears. In fact, working over a span of a few years park staff have reduced the number of pears in Columbia’s downtown from 5 percent to 1 percent of the total tree population, illustrating that beautiful tree canopies in parks and downtowns can be accomplished without ornamental pears.

The Best Defense

What can homeowners and landowners do to help? Consider diversifying the next time you plant a tree and avoiding ornamental pears or any other non-native trees with invasive tendencies. Secondly, prune off any sprouts that grow from the base of your ornamental pears to prevent crossbreeding with the sprouts and tree itself. Lastly, if you have ornamental pears consider replacing them with a different kind of tree once the pears decline or are damaged.

There are several interesting choices of native, small to medium flowering trees, such as downy serviceberry, yellowwood, redbud and hornbeam. A great reference when trying to select trees to plant in your yard or town is the publication Missouri Urban Trees. This full-color booklet with photos is free and available at Missouri Department of Conservation offices. You can also view it online at mdc.mo.gov/node/8045. Anne McKinstry, with the Missouri Nursery and Landscape Association, also suggests contacting your local, independent garden center. You can use their expertise to find the right tree for your situation and head off future problems.

If you spot wild callery pears on your property, control them by cutting them down and immediately treating the stumps with appropriate systemic herbicide to prevent them from re-sprouting.

It is yet to be seen how much damage wild callery pears will cause. Certainly there are fields that are already inundated with them. However, due in large part to the proactive efforts of citizens, we are learning about this problem fairly early.

So, keep your eyes peeled for wild callery pears and remember … STOP THE SPREAD!

Special thanks to Brett O’Brien, Natural Resources Supervisor with Columbia’s Parks and Recreation Department, for collaboration on this article.