Bramble Rust Diseases

This is from Team Rubus at North Carolina State University – potential new disease?

New Rust disease?

Posted: 29 Mar 2012 02:53 PM PDT

Spring is the time of year when we usually see the first signs of a disease known as Orange Rust. Orange Rust is a systemic disease that is very hard to control, once a plant is infected.  One of the tell tale symptoms are bright orange spots on the undersides and margins of leaves and a spindly overall appearance of the plant. This spring some growers are seeing orange spots on blackberry leaves, but the symptoms are not what we expect…

Below is an email that was just sent out from Dr. Phil Brannen. Growers in the SEUS should be  on the lookout for plants with these symptoms and use your state disease clinic or specialists to help you identify the potential causal organism….
“Commercial blackberry producers should be on the lookout for blackberry rusts (there are several), and they should likewise be maintaining a good rust control program through use of cultural practices and fungicide applications.  Conditions may be particularly conducive for rust development this year due to a warm fall and winter.  There is also the possibility that we are observing a new rust on blackberries in the Southeast.
Last week, a Natchez thornless blackberry specimen was submitted to the UGA diagnostic clinic in Athens.  Though we sometimes observe orange rust as the leaves emerge in the spring, we did not observe typical symptoms of orange rust, and the spores did not match those of other common blackberry rust diseases.  Also, the producer indicated that all of his Natchez plants were showing this rust symptom, and that would be very unusual for orange rust, as it is usually limited to only a few plants.  Today, I received questions from North Carolina as to rust issues there.
Charles Hodges (North Carolina State University) writes of a rust on a Navaho thornless blackberry sample:
“I have had a lot of trouble trying to identify the rust species on the specimen of blackberry submitted and am still not sure of just what it is. The symptoms are not consistent with those of orange rust which is characterized by stunted and misshapened leaves, nor are the fruiting bodies and spores similar to orange rust. The rust fruiting bodies and spores on the underside of the leaves more nearly fit the uredinial stage of cane and leaf rust (Kuehneola uredinis). However, there is no evidence of the spermagonial, aecial, and telial stages that should be on the same infected leaf at this time of year. Furthermore, I could not find any fruiting bodies of the rust on the canes, which is common with the cane and leaf rust.”
This description from North Carolina, though highly technical, perfectly matches our Georgia observations as well. It makes me think that we are dealing with a new rust or one that is problematic as a result of the warmer weather we have experienced this year.
Producers are automatically assuming that this is orange rust due to the timing, and our general recommendation for orange rust infected plants would be complete plant destruction, since it is a systemic rust disease.  However, we have never seen orange rust take over large acreages to date — always isolated plants in well managed commercial blackberry plantings.  DO NOT assume orange rust and DO NOT automatically dig up symptomatic plants till you truly confirm orange rust is the culprit.  If a specimen is identified as orange rust (county agent can often just send a photo of the symptoms or a hard sample can be sent to the diagnostic clinic in Athens), then we would recommend complete destruction of infected plants.  There may in fact also be more orange rust this year as well, since a warmer fall/winter has possibly allowed a second round of infections — likely in the fall of last year.  Orange rust management requires fungicide application from early bud break through early to mid-summer, and this normally addresses other blackberry rusts as well.   Follow rust disease management guidelines found in the Blackberry IPM Guide at www.smallfruits.org
Again, don’t dig up anything till you truly confirm orange rust.  Based on these initial reports, our current blackberry rust is either a new rusts or one that is generally present but not normally problematic.  Please share this information with your commercial blackberry producers, as they need this information to help them in their management decisions. “
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