Combatting Rose Cane Canker

by Gregory Constant, Master Rosarian, Baton Rouge Rose Society.

Central Louisiana Rose Society thanks Gregory Constant, Baton Rouge Rose Society member, for taking the time to document his personal combat and victory in the battle that has confronted many Louisiana rosarians the past few years.

ROSE CANKER

With the heavy rains of 2016 plaguing the Gulf Coast with unprecedented moisture, it brought with it an outbreak of Rose Canker, also known as Coniothyrium, that has taken residence in many rose gardens across the coast.

If left unmanaged, rose canker will eventually kill a rose bush. Rose cankers will often appear as black splotches on the canes of rose bushes. If the pathogen is present on a rose bush and the bush is pruned with the disease going unnoticed, it is then transmitted to the next bush when pruned if the pruners are not first wiped with a disinfectant. It is therefore imperative that the infected cane or canes are removed down to a good clear

healthy green cane tissue just below the canker. After all signs of canker are removed from the bush a soil drench to the bush is recommended to eliminate the canker or at least get it to a manageable stage. ABOVE: Actively growing canker with sporulation visible between the healthy green stem to the left and sprouting from the brown diseased cane on the right. A rose bush with the Canker disease that went unnoticed and is too far gone to treat. LEFT: Signs of canker untreated.

Prior to drenching, I searched the entire garden for signs of canker and cut out all canes with the disease. The photos below are progression of the disease being cured. It is obvious on this rose specimen which I have used for demonstration purposes, that IF caught in time, the healthy side of a cane will heal over and cut itself off from the once diseased part and thus continue to grow. LEFT: Second week after two treatments with Cleary’s 3336. Indications are that Canker is successfully dying as the diseased cane begins to turn a pale brown.

LEFT: Eight weeks after treatment with Cleary’s 3336 the rose bush has fully recovered from the canker and shows signs of vigorous new growth and blooms. The back side of the cane shows healthy growth and the dusty brown side of the cane that is visible indicates that the treatment was successful and the canker is dead. Plants have the ability to block off the diseased portion of a stem or cane and continue normal healthy growth on the side that is not affected.

LEFT: HEALTHY BASAL BREAK AFTER 10TH WEEK OF TREATMENT.

In conclusion, a rose bush that suffers from Canker can be successfully treated if caught in time. But like any other disease that affects roses, it is always easier on the bush and the rosarian if a close vigil is kept on the garden. With a close vigil, abnormal growing conditions are noticed as soon as they happen and the necessary treatment is immediately implemented.

Photos by Gregory Constant