Last year my Bradford Pear’s leaves were covered with rust fungus. What can I do this year to prevent that from happening again? CS

You are correct. It seems like rust disease was everywhere last spring. There are a variety of rust diseases such as cedar-apple rust, Asian pear rust, cedar-hawthorn rust, and cedar-quince rust to name a few. While these diseases are not terribly harmful to their host, they can diminish the vitality of the host plant and reduce production on fruit trees. You mentioned Bradford Pear, which is an invasive species, but first let’s talk about rust disease prevention.

The funny thing about these rust diseases is that they require two different host plants to prosper. Cedars or junipers are the host during one portion of the life cycle and other plants like Bradford Pears are the host during the other portion of the life cycle. Asian pear rust is the culprit when it comes to Bradford Pears.

The fungal spots we see in the spring on Bradford Pear leaves were blown there by the wind from a nearby cedar. Nearby is kind of an oxymoron since nearby could be within a mile or so.

The fungal spores continue to grow on the leaves of the Bradford until June or July when they release spores of their own that are blown by the wind to a nearby cedar. The fungal spores grow on the cedars until the next spring when rains cause the rust to release their own spores which are blown by the wind back to the Bradford and others.

The Asian pear rust cankers are relatively small, but the cedar-apple rust galls are more likely to be golf ball sized. One very interesting thing about the pear rust’s cousin is that the golf ball sized cedar-apple rust galls, when soaked by the spring rains, push out these long orange gelatinous tendrils. These tendrils are full of spores which the wind is more than happy to relocate to your apple trees. It is a very interesting, if not creepy life cycle.

If you decide to try and prevent this disease, you will need to spray your broadleaf (not the cedar) from leaf emergence through April on 7-10 day intervals with a fungicide such as copper hydroxide, chlorothalonil, myclobutanil, or propiconazole (use as specified on the labels).

The cedars can be treated in late June-July with the same fungicides. However, you can always physically remove the larger cedar-apple rust galls from the cedars when you see them. Pear rust is harder to find on the cedars.

Fruiting trees have slightly different needs, and you can find a fruit tree spraying schedule in the Fruits, Nuts, and Berries section of our Lawn and Garden Help page on our website.

Now, let’s circle back around to your Bradford Pear. Bradford Pears (Pyrus calleryana ‘Bradford’) were introduced to the United States in the early 1900’s as a way to help control fire blight of the common pear. By the 1980s it had become the second most popular ornamental tree in America.

The Bradford Pear is known for the white flowers they produce in the spring. While the flowers are pretty, they also have a rather unpleasant smell, oftentimes associated with the smell of fish. Ok, so that’s kind of a downside.

All was well with the Bradford until something unexpected happened. The Bradford was originally bred to be sterile and thorn-less. However, when cross pollinated, they can produce fruit. These small 1/2” diameter fruits are kind of like small, hard apples with greenish-yellow flecks and white spots. They are not edible, but these fruits do contain seeds.

After fall freezes, the fruit softens and becomes edible for birds who then help spread the seeds. Unfortunately, the trees that grow from these seeds are not Bradfords but are trees that have reverted back to the thorny variety from which they originally came. This life-cycle causes these trees to become very invasive, displacing native natural habitats.

You will begin to see the problem any day now when driving around town. When you are cruising down one of the expressways in a somewhat rural area, if you look around, you will notice outcroppings of some typically densely packed trees with white flowers, those are more than likely the unfortunate spawn of our Bradford pears.

Since the horticultural community became aware of this issue, there have been many efforts to discourage the use of the Bradford in home landscapes. However, they are still available from a variety of retailers. Our general recommendation is to find another tree you might like rather than plant a Bradford. Several communities around the country have offered to provide replacement seedlings of a more environmentally friendly tree for those willing to remove their Bradfords. As of yet, Tulsa is not among them.

For more information of types of trees that do well in Tulsa, visit the Trees page in the Lawn and Garden Help section of our website.

You can get answers to all your gardening questions by calling the Tulsa Master Gardeners Help Line at 918-746-3701 or by emailing us at mg@tulsamastergardeners.org.