Breneria (formerly known as Erwinia) is a genus of bacteria that causes serious diseases in walnut trees. The two main forms of the disease caused by these pathogens are:
- Shallow Bark Canker – caused by Breneria nigrifluens.
- Deep Bark Canker – caused by Breneria rubrifaciens.
These diseases lead to the appearance of necrotic lesions on the bark of the trees, weakening their vitality and reducing yield. In more severe cases, particularly with deep bark canker, the infection can lead to the death of the trees.
Symptoms and Diagnosis
-
Shallow Bark Canker
This disease develops slowly and does not lead to significant economic losses, but it can weaken the trees over time. The main symptoms include:
- Brownish-black spots on the trunk and lower branches.
- Watery and sticky spots that dry out and turn into sunken, dark lesions.
- Primarily affects older trees, but rarely causes their death.
-
Deep Bark Canker
This is a more aggressive form of the disease that can lead to serious economic losses. The main symptoms are:
- The leakage of dark brown or reddish fluid from infected areas ("bleeding" bark).
- Black discoloration of the internal tissues beneath the affected areas.
- Spread of the infection into the deeper layers of the bark, which can significantly weaken the trees.
- In severe cases, trees may die if the infection spreads uncontrollably.
Diagnosis of the diseases is performed through visual observation and laboratory analysis of bark samples, using molecular and microbiological techniques to identify the pathogens.
Causes and Mechanisms of Spread
Bacteria from the Breneria genus spread through various mechanisms that facilitate the infection of new trees:
- Wounds on trees – Mechanical injuries from pruning, hail, insects, or shaking of trees during harvest can serve as entry points for the bacteria.
- Spread through rain and wind – Raindrops can carry the bacteria from infected to healthy trees.
- Infected seedlings – Young trees can be infected during planting if they come from infected nurseries.
Management and Control Methods
Given the lack of effective treatment for advanced stages of the disease, integrated prevention and control strategies must be applied:
- Maintaining Tree Health
- Optimal irrigation – both excessive moisture and drought should be avoided, as they can weaken the trees and make them more susceptible to infections.
- Fertilization – the use of balanced fertilizers helps enhance the overall resistance of the trees to diseases.
- Avoiding mechanical injuries – this is especially important during mechanized harvesting.
- Controlling the Spread
- Disinfection of tools – Pruning shears and saws should be sterilized with a bleach (10%) or alcohol solution after working with each tree.
- Avoid pruning during wet weather – wet conditions favor the spread of bacteria.
- Removal of infected branches – infected parts should be burned or removed far from the plantations.
- Chemical and Biological Control
- Copper-based bactericides – these limit the spread of the pathogen but cannot fully cure infected trees.
- Biological agents – beneficial microorganisms can suppress the development of Breneria through competition or antagonistic mechanisms.
- Antibiotic treatments – the use of antibiotics is limited due to the risk of resistance and regulatory restrictions.
Breneria (formerly Erwinia) represents a serious threat to walnut plantations. Although there is no completely effective treatment for advanced cases, proper management of the plantations and the strict application of agro-technical measures can significantly reduce the risk of infection and limit the spread of the disease. Regular monitoring of trees and the use of integrated control methods are recommended to reduce production losses and maintain the health of walnut orchards.
