Strawberry Bacterial Leaf Spot, or Angular Leaf Spot, is a detrimental bacterial disease that poses significant threats to strawberry crops.
In the world of strawberry cultivation, one bacterial disease stands out as a persistent threat: Angular Leaf Spot, caused by the bacterium Xanthomonas fragariae. This disease thrives in wet, crowded conditions and can be challenging to manage once established. However, with a strategic approach that combines cultural, biological, and sanitation measures, growers can effectively control this disease.
One of the most critical steps in preventing the introduction of Angular Leaf Spot is the use of certified disease-free plants. While nursery stock is certified to be free of viruses, it's essential to remember that this certification does not extend to bacterial or fungal diseases. Selecting planting sites with good air circulation and full sun exposure is also crucial, as it promotes rapid drying of foliage, which discourages bacterial growth.
Controlling weeds in and around the strawberry bed is another essential measure. By reducing humidity and potential sources of infection, weeds can help prevent the spread of Angular Leaf Spot. It's important to avoid overhead irrigation, as water splashing can spread bacteria and keep leaves wet longer, favouring disease development. Instead, opt for drip or trickle irrigation systems.
After harvest, it's crucial to remove and dispose of all infected plant debris. Composting or soil incorporation is recommended to reduce overwintering inoculum. Floating row covers may also be used to protect plants, particularly early in the season, by reducing leaf wetness and inoculum spread.
Crop rotation is generally ineffective against this disease, but maintaining good sanitation and cultural practices helps manage it. Biological controls such as Streptomyces-based products (e.g., Actinovate AG) offer bacterial and fungal disease suppression without resistance risk and are safe for beneficial insects. These can be integrated into management plans.
Regular scouting and prompt removal of symptomatic leaves can further reduce pathogen spread. Under high-moisture conditions, bacteria may ooze from lesions on the undersides of leaves and get splashed to other tissues to cause new infections. As infected leaves age, lesions on the upper side of leaves may appear as reddish brown necrotic spots. Entire leaves may die if major veins become infected.
When moist, lesions on the leaf undersides may secrete a viscous ooze of bacteria. In spring, the bacteria become active in systemically infected plants, and disease symptoms develop. The bacterium does not survive freely in the soil but instead survives on previously infected dead leaves on or in the soil, and on the crowns of systemically infected (live) plants.
Calyxes can also become infected and turn brown or black, resulting in unmarketable fruit when severe. The bacterium is generally introduced into a planting on symptomless, systemically infected nursery plants. To minimize spread of Angular Leaf Spot within infected fields, avoid moving equipment or harvesting when plants are wet.
While fungicides are generally not effective against bacterial diseases, Oxidate (hydrogen dioxide 27%) is registered for control of Angular Leaf Spot on strawberry. However, prevention and cultural control remain the key strategies for managing this disease.
Incorporating the use of Streptomyces-based products, such as Actinovate AG, into health-and-wellness strategies for strawberry cultivation could potentially suppress bacterial and fungal diseases, including Angular Leaf Spot, without the risk of resistance and while being safe for beneficial insects. For medical-conditions like Angular Leaf Spot, maintaining good soil health and following scientifically-proven practices, like selecting disease-free plants, promoting air circulation, controlling weeds, and using drip irrigation systems, can significantly contribute to preventing and managing this bacterial disease.
