Orange Rust on Thornless Blackberries

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Recently in Northeast Ohio, the fungal disease known as Orange Rust is beginning to rear its unique, but strange symptoms on brambles, which are also known as cane berries.  Specifically, this fungus most often infects black and purple raspberries and sometimes is found on thornless blackberries, but is not known to infect red raspberries.

For me personally, this is the first time in my 24 years as an Extension Educator, that I have seen this disease on thornless blackberries.  Most often, this fungus is evident on either thorned blackberries or purple raspberries.  It is classically diagnosed/identified early on by the off-colored, yellowish-green, spindly new cane growth with the leaves also being twisted or deformed.  If those spindly, elongated canes are left alone and some leaves partially develop, the lower leaf surfaces of those leaves will develop blister-like masses (pustules) of yellow-orange spores.

Healthy blackberry plant on left & Orange Rust infected on right
Healthy thornless blackberry on left & Orange Rust infected plant on right

Everyone wants to know how to control this disease and therein lies the problem, because this fungus grows systemically throughout the entire plant!  The recommended and best control of this fungal disease, is to remove and destroy ALL OF THE PLANTS, other than red raspberries, in the planting.  This is due to the root grafts, which develop easily and are very common between plants.  Due to these root grafts, the fungus can rapidly spread from plant to plant and throughout the entire planting, hence the remove and destroy approach.

Orange Rust pustules on underside of blackberry leaves
Orange Rust pustules on the underside of infected thornless blackberry leaves

It is recommended that no black or purple raspberries are planted back in that area for 2-3 years, to ensure that any remaining pieces of roots, if they begin to grow, can be dug up and destroyed.

Appearance of infected blackberries
Overall appearance and vigor loss of infected 'Triple Crown' thornless blackberry plants