by Ann Barnes
Whether you love them or hate them, Bradford pears are eye catching when in bloom. Right now, the Bradford pears are catching our eyes for a different reason – diseases. These trees were bred for disease resistance, but that doesn’t mean they are immune if conditions are favorable. If the Bradfords in your neighborhood have brown leaves and you’re wondering what could be wrong, read on.
Photo credit: Roger Meissen/MU Cooperative Media Group
Fireblight is a bacterial disease caused by Erwinia amylovora. The characteristic symptom of the disease is blackened branches that look like they were burned. The tips of the affected branches curve into a “shepherd’s crook” shape. Per Michelle Wallace, Durham County Horticulture Agent:
Fireblight is a bacterial disease that is spread by flies when the bradford pears are in bloom. The flies are the dominate pollinator of this plant – hence the malodorous fragrance from the flowers. The flower’s scent is suppose to fool the flies who are looking for a place to lay their eggs and prefer rotten meat or dung. If the fly comes in contact with an infected host flower the disease will be spread to every susceptible flower it comes in contact with. Not a new problem around here, I have seen this problem on Bradford pears for years.
The recommended treatment is to prune out the infected wood, 6 -8 inches below the dead limbs. Make sure to clean pruners with an anti-bacterial wipe in between cuts. When the tree is in bloom it can be sprayed with streptomycin sulfate – a type of plant anti-biotic. However, I recommend just taking down the tree and replacing it with a tree that has no insect or disease problems. Bradford pears are short lived with many known problems including splitting of the limbs. It is more expensive and time consuming to invest in saving this tree than replacing it with a better one. In addition, there are environmental and safety issues related to spraying anti-biotics.
Cool, wet conditions (such as we had this spring) are favorable for the spread of fireblight. With many Bradford pears planted in our area, there are lots of host plants to spread the disease.
Quince rust on Bradford Pear, Photo: Ann Barnes
Quince rust on Eastern Red Cedar, Photo: Mike Boehm, The Ohio State University
Quince rust is caused by the fungus Gymnosporangium clavipes. The fungus has a complex life cycle that requires two types of host plants to complete. This disease is often referred to as Cedar-Quince Rust because cedars and other members of the Juniperus family are host plants for one phase of the life cycle. The fungus overwinters in swellings on plants in the juniper family. In spring, gelatinous orange spore horns (teliospores) are produced, which germinate to produce basidiospores. These basidiospores are carried by wind to nearby Bradford pears, crabapples, hawthorns, and other susceptible trees. Again, wet spring weather is favorable to the spread of this disease.
Quince rust can affect twigs, leaves, and fruits of the second host (in this case, the Bradford pear in our previous photo). Leaf loss can occur due to infection, which could weaken trees.
Several weeks after the Bradford pear’s infection, another type of spore-bearing structure called aecia are formed in the infected plant tissue. These aecia produce spores that are carried by wind to infect more cedars or junipers, continuing the cycle.
Control of rust diseases requires monitoring both hosts and removing infected tissue. Fungicide is not generally recommended for rust on ornamental trees in the home landscape. Removing infected Bradford pears and replacing with a different, resistant tree is still the most environmentally friendly and cost effective method for dealing with a severe infection.