Pear Rust
Pear trees, such as the ornamental ‘Bradford’ pear, have become a very popular landscape plant and street tree over the past couple of decades. Favored for their showy spring blooms, adaptability to pollution and general disease resistance, pear trees can be seen in nearly every urban and suburban setting throughout its range.
Pear rust is a fungal disease occurring on pear trees; however the disease requires multiple hosts to complete its life cycle and so affects junipers as well. Caused by the fungus Gymnosporangium sabinae, pear rust will appear as orange colored leaf spots on pears in the summer and fall and year round cankers on juniper trees. Accidentally introduced from Europe, there is now potential for this disease to develop wherever pear and juniper ranges overlap, which encompasses the eastern seaboard as far north as Massachusetts and south to Georgia and as far west as Illinois.
How can I tell if my pears or junipers are affected?
Junipers present with perennial cankers on stems and branches which produce orange, horn-like outgrowths in spring when the temperature and humidity rise. Pear trees will have bright orange spots on upper leaf surfaces, with brown gall-like growths developing on the lower leaf surface as the summer progresses.
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Oak Wilt
Oak species make up large majorities of native landscape and natural forests throughout the country. Some species are susceptible to pest issues but most residential problems can be controlled with regular monitoring and maintenance. However, oak wilt is an aggressive disease affecting many species of oaks killing thousands of trees each year in forests, woodlots and home landscapes.
Oak wilt is caused by the pathogenic fungus, Ceratocystis fagacearum, thought to be native to the United States. It is considered one of the most serious diseases in the country right now. While all species in the Quercus genus appear to be susceptible, those that are considered red oaks seem more seriously affected. Trees in the white oak group may take years to die from this disease or can even recover, while red oaks may die within a year of infection.
How can I tell if my oak trees affected?
Oak wilt is a vascular disease, which infects trees through root grafts and is transmitted by sap-feeding bark beetles. Symptoms are characterized by wilting and bronzing of foliage beginning at the top of the tree and quickly spreading throughout the crown. First signs of oak wilt will present in May and progression of the disease will continue during the growing season. Individual leaves bronze quickly from the tip spreading to the base, sometimes leaving a small green area near the midrib. Leaves in all stages of discoloration will begin to drop prematurely. Bronzing and defoliation is less pronounced in white oaks and may only be visible on a few branches. In both groups, trees of all ages may be affected.
What can I do to prevent the spread of oak wilt?
Local spread among trees occurs naturally through root grafting between closely growing trees or through feeding and tunneling activities of insects. Transport of infected nursery stock and firewood, particularly those bearing oak bark beetles will help spread the disease over longer distances. The best approaches to inhibiting the spread of oak wilt culturally is to prevent introduction of the fungus and beetles by refraining from transporting firewood and nursery stock and spacing trees appropriately when planting. Monitoring and removal of infected trees will also help stem the spread of infection, as will keeping trees on your property healthy and free from inadvertent wounds.
