Ron Wilson

Ron Wilson

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Flowering Ornamental Pear. How invasive is it? - Thomas deHaas Ann Chanon

Why was Flowering Pear added to the invasive species list making it illegal to sell as of January 7th, 2023.


The proof is in the flowers. Now’s the time to spot it in Northern Ohio.


On January 7th, 2023, it became illegal to sell flowering pear in Ohio. The following post spells out the details:


Ohio Department of Agriculture Inspectors and Ohio State University Agriculture and Natural Resource Educators are keeping an eye out for any garden centers or outlets that may offer Flowering Pear or its varieties for sale in Ohio.


How bad is it?


Just driving down any road or freeway, you can pick out escapes. They stick out like a sore thumb. And usually not far away are the parent trees in a landscape setting. Initially, Bradford Flowering Pear was incompatible with self-pollination.


A great article publish by Arnold Arboretum explains the entire story. It is titled: "The Rise and Fall of Callery Pear"


Ann Chanon states, "This probably the best nonacademic explanation of why Callery pear was brought here and the subsequent issues. As you will read, genetic self-incompatibility is not absolute. In the “ sterile trees” they were observing some fruit set."


This is from the article” The answer lies in the reproductive system of the species as well as its horticultural history. As with most other pears, Pyrus calleryana has a genetically controlled self-incompatibility system that prevents individual trees from pollinating themselves, thus requiring outcrossing among unrelated individuals. When ‘Bradford’ was first introduced and became so wildly popular, ‘Bradford’ trees were unable to cross-pollinate (since they were all genetically identical) and fruits were never produced. As additional cultivars were introduced, they were often commercially marketed as “self-sterile” or even “seedless”—this was true, as long as each cultivar was grown in isolation. Cultivar patents and promotional material included notes such as “[fruit set] very low (about 5 to 10%), usually only one fruit per cluster” (‘Autumn Blaze’); “little or no fruit and the fruit that is produced is small and hard” (‘Trinity’); and “self-sterile” with fruits typically not abundant and only produced when “planted near another clone”(‘Aristocrat’). The last point is the lynchpin of this story.


Although each Callery pear cultivar cannot produce fruits on its own, fruits can easily develop when two or more cultivars—which are genetically different and therefore cross compatible—are planted together (Culley and Hardiman 2007). For example, if a large residential area only contains ‘Bradford’ trees, no fruits would be formed. But if a new resident moves in and plants a single ‘Aristocrat’ in her yard, that new tree now has the potential to cross-pollinate all the ‘Bradford’ trees within a mile-wide range, and vice-versa. This could trigger a sudden outburst of fruit within a single year.”


A new introduction, a triploid claim to be 99% incompatible. It is referred to as Pyrus "Chastity"


Regarding this cultivar, Ann Chanon states, "Here is the plant patent for the new triploid pear out of North Carolina. Basically, they crossed a tetraploid plant with 4 sets of chromosomes with a diploid plant with two sets of chromosomes and the progeny have three sets of chromosomes. Because not all the chromosomes can align during chromosome replication and division triploids are usually sterile. There are always a few reproductive cells that revert either to a diploid or maintain a tetraploid chromosome configuration which are fertile.",788


It has not been approved to be sold in Ohio.


The conclusion is, Flowering Pear IS invasive. That’s why it cannot be sold in any form in Ohio.


In an effort to remove Flowering Pear, Now is the time. By cutting it down at the base before it sets fruit, you can slow the spread.


As removing any invasive plants, painting the base with a herbicide after pruning can help reduce the chance of suckering.


A resource on removal and techniques if found below:


Even though this fact sheet in regarding Tree of Heaven, the same techniques can be applied.


ODNR has the following information on Flowering Pear:


Flowering Pears are beautiful, but they are still a problem and will be for years to come.

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