Tag Archives: Rust

October 4, 2013

Check for Fir Rust Disease

Fir Broom rust is becoming more common in New York as the number of fir tree plantings increase.  This disease produces a proliferation of shoots “witches brooms” that can make the tree unsalable.

Severe Fir Broom Rust can cause losses for growers.

The fall and the upcoming sale season, are a good times to see if it is present in the field.  When taking off the bottom limbs of trees be sure to take notice if any brooms are present. Also when the trees come in during harvest season keep an eye out.

It can be difficult to detect the small “brooms” at first

Hidden broom

Because the affected growth is shorter than the surrounding branches it is often hidden.

The disease often shows up on the lower branches first where the rust fungus benefits from increased moisture in the shaded lower canopy. The lower branches are also to the source of the spores that are coming from the chickweed plants.  The infection of the firs happens in the spring when rust spores travel from chickweed to fir tree needles at bud break.  With enough moisture those spores can germinate, penetrating the needles and later in the season  producing  spores on the needles that can only infect chickweed, continuing the cycle. Both mouseear and common chickweed are susceptible to this disease.  These weeds often grow unnoticed amongst grasses in Christmas tree fields.

Mouseear & common chickweed. (Click for expanded view.)

There are no fungicides registered to control this disease on fir trees.  Fortunately it can be managed by controlling the chickweed in the field with broadleaf herbicides.

For more information see this factsheet: http://nysipm.cornell.edu/factsheets/n_gh/fir_broom_rust.pdf

May 21, 2013

Quince Rust on Junipers

Another rust disease in the cedar rust group, quince rust is the most likely to cause serious dieback on junipers.

With this disease the bright orange “galls” are actually just slightly swollen lesions on the stems. Widespread lesions can lead to significant browning of the branch tips as pictured above. Spores which spread from these galls in the spring infect the alternate hosts of quince, hawthorn, crabapple or apple tree leaves. On hawthorn trees this disease causes causes symptoms on the leaves, white fringes on the fruit and swellings and distortion of the branch tips.

As with  similar rust diseases separating the juniper from the alternate host (the further apart the better) can help keep this disease in check.

For lists of resistant varieties and fungicides labeled for managing this disease refer to the Disease Section of  Cornell Guidelines for Commercial Production and Maintenance of Trees and Shrubs.

May 14, 2013

Hawthorn Rust

Bright orange swellings can be seen at this time of year on some Eastern redcedars and other junipers.  After a rain those small, translucent-orange galls with gel-like projections appear.  These weird galls are caused by an intriguing fungus that needs two different host plants to live!

Hawthorn rust galls on Eastern redcedar.
Photo take in May, Onondaga County, NY.

Close up of galls. (Click for expanded view.)
Photo take in May, Monroe County, NY.

In the spring the orange masses expand after a rainfall and release  spores that can travel though the air and only infect the leaves of a hawthorn, apple tree or similar host (see below).  Then in the fall, from spots that formed on the hawthorn or apple leaves, spores are produced that can only infect a juniper/cedar.  The cycle continues in the spring when you can see new galls on the juniper/cedar.  Although a problem for apple growers this rust disease does not cause serious harm to the junipers.   There are other rusts that can cause problems with junipers such as quince rust.

In addition to the foliage of hawthorn and apples this disease can occasionally affect the leaves of affect crabapple, service berry or quince or pear.  However this disease does not affect any other evergreen tree species.  Only  redcedars and junipers can become infected.