Graft canker

Graft canker, caused by the fungus Coniothyrium rosarum, is a destructive disease primarily affecting rose bushes. This pathogen attacks the stem tissues, specifically targeting the bark and cambium, which can severely compromise the structural integrity and health of the entire plant.

The first clinical signs of the disease appear in early spring as reddish-brown spots on the stems. These spots gradually darken and expand, often resulting in deep, sunken lesions. As the infection progresses, the centers of the cankers turn light brown or grey, frequently showing small black fruiting bodies of the fungus beneath the ruptured bark.

Environmental conditions play a critical role in the development of Coniothyrium rosarum. High humidity levels, poor ventilation within winter coverings, and significant temperature fluctuations create a perfect environment for fungal colonization. The pathogen enters the host through wounds, pruning cuts, or frost cracks, spreading rapidly during cool and moist periods.

The impact of this disease is significant, as it leads to the girdling of stems. Once the fungus completes a circle around the shoot, the flow of nutrients and water is obstructed, causing the foliage to wither and the stem to die back rapidly. Severe infestations can lead to the loss of large sections of the bush or total plant death.

To control and prevent the spread of graft canker, growers should adhere to the following practices:

• pruning and destroying infected branches immediately to prevent spore dispersal;
• sanitizing pruning tools with disinfectants between cuts;
• applying copper-based fungicides as a preventative measure in early spring;
• ensuring optimal ventilation in winter covers to reduce humidity;
• maintaining plant vigor through balanced nutrition and adequate irrigation.