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WICHE: Rust diseases travel between host plants

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This is a difficult problem to identify and to eradicate.

By Jeneen Wiche

Last year our serviceberry was afflicted with a whimsical-looking disease. Those beautiful blue berries that appear in the summer looked like something from a Dr. Seuss book. In a good year the cedar wax wings usually flock in and eat the berries as they ripen. Not so last year.

The strange, white, tubular protrusions that covered the berries were not only funny looking, but they kept the birds away, too.

This rust disease happens from time to time, infecting the fruit of various plants around the farm. It is a cycle of disease that takes two years to complete its journey, and it is becoming more and more commonplace in the landscape.

If you are a home orchardist, you will want to familiarize yourself with the dynamics of cedar-apple rust.

Many rust diseases must have two specific hosts for the disease to complete the various stages of its life cycle. For example, the fungus that causes cedar-hawthorn rust needs a juniperus species, like the eastern red cedar or an ornamental juniper (which are ubiquitous in our landscapes) to spend its parasitic stage of life.

During the parasitic stage of life, the fungal spores appear in the springtime as bright orange teliospores on the host cedar. As these teliospores develop ,they are carried through the air to the next host plant. These other hosts must be roseaceous, like apples, hawthorns, crabapples or serviceberries.

While on the second host plant, the rust disease continues to develop into the fruiting stage that then travels back to re-infect nearby cedars or junipers.

Apparently after 18 months in this stage, the spores return in the second spring to start all over again if the conditions are favorable. Wet springs often are followed by a higher incidence of rust diseases. What will our cold spring bring?

All of the various rust diseases are caused by specific species of the fungus gymnosporangium. The fungus must travel between a juniperus species and some roseaceous plant and back again.

However, there are different types of rusts. Cedar-apple rust primarily infects the foliage of apples and crabapples. Yellow spots appear on the foliage in the spring, turning orange as the season progresses.

Whitish, tubular spores will develop around these spots by summer. This seems to be the most distinguishable characteristic for diagnosis.

Cedar-hawthorn rust appears on hawthorns, apples, crabapples, pear, quince, service berry, and mountain ash. The appearance of this rust disease is similar to cedar-apple rust, but the white, tubular spores are not present, just the leaf spots.

Cedar-quince rust proves to be the most damaging to plant material. The list of susceptible plants includes those mentioned above plus quince, photinia, medlar, chokeberry and cotoneaster.

The foliar spots are not apparent here. Rather the infection is manifested in the twigs and fruit of the plant. Young twigs that become infected can die. Repeated infection can cause the decline of the tree.

If you consistently struggle with rust diseases, consider growing disease-resistant varieties and removing any old, abandoned or worthless host trees. The spray regimen for controlling cedar-apple rust is a difficult formula to follow for it to be successful, so reasonably our best bet is to manage the problem by removing old cedar trees in the fence row.

For home owners this may be limiting the overuse of junipers in the landscape. Watch for orange spores on juniper species this spring and remove any that you see to offset the spread of the disease.

 

Check out gardening columnist Jeneen Wiche’s work at www.SwallowRailFarm.com. You can find her columns also at www.SentinelNews.com/agriculture. She answers questions once a month in SentinelNewsPlus. To submit a question, send an E-mail to jwiche@shelbybb.netand type “Sentinel-News” in the subject field.