Georgia Gardener Newsletter Ask An Arborist: April 25, 2013
Orange Growth in Trees
Image Submitted by Donald B.
Image Courtesy of Walter Reeves
Donald B. writes a very short question: "What the heck is growing on my tree!"
What Donald is seeing is one half of the life cycle of a fungus that we commonly call cedar-apple rust. There are similar diseases
called cedar-hawthorn and cedar-quince rust. The one thing these fungal diseases have in common is they alternate hosts from
cedars (actually junipers) to plants in the Rosaceae (Rose) family.
The cedar-apple rust fungus begins life as an swollen or woody appearing gall on juniper plants (Juniperus spp.).
These junipers can be the common wild Eastern red cedar or any number of upright or prostrate junipers found in the landscape.
This gall will eventually mature and "bloom" into an orange gelatinous "glob." In the glob phase of its life, the fungus
will produce thousands of spores that will be carried away by wind. Although unsightly, the woody gall and mature orange
fungal growth do little harm to the junipers. You can simply remove the growth and discard it in a plastic bag.
The second half of the cedar-apple rust life cycle is where the real damage occurs. Once spores leave the cedar they are wind
carried and if they land on susceptible host, will grow to produce hundreds of yellow to red spots on leaves and fruit. As you may
guess, the second half of the life cycle occurs mainly on apples and crabapples. The fungus can severely damage leaves causing
early defoliation and also damage the fruit. These fungal spots on apples will produce spores that find their way back to the
original host - a juniper.
The juniper gall produced by cedar-hawthorn rust is smaller and may live for several years. It can cause twig dieback in
junipers. The second half of the cedar-hawthorn rust life cycle can be
found on hawthorn, pear, quince and serviceberry. It also attacks apples and crabapples where spots similar to cedar-apple rust
are produced.
Cedar-quince rust is the most destructive as it attacks a wide range of hosts from quince to cotoneaster, chokeberry, mountain ash
and hundreds of other plants. It tends to affect stems and fruit more than the leaves and will overwinter in affected stems. In
junipers it can produce galls that will girdle and kill stems and branches.
Control
The best way to control these diseases is to break the life cycle by removing one host from the equation. This may be difficult as
the spores can travel great distances by air. Remove growths from junipers immediately and discard them in plastic in the trash.
Try to plant only resistant cultivars of junipers and Rosaceae family plants. A list of which is provided
here.
The fungicide Immunox and Bayleton are effective in treating these rust diseases on fruit and other secondary host plants. They should be applied
very early in the season and repeated about every 7-10 days for several weeks. You can also use these products to treat junipers, but
the application should be done during the summer months. Always read and follow the label directions of
any garden chemical product you plan to use before you purchase it and before every use.
Please email me if you have any questions or topics you would like to submit
for later articles.
