The fungus Septoria lycopersici causes a Septoria leaf spot, affecting tomato plants’ foliage. The fungus infects the leaves through natural openings or wounds. It causes small, circular, brown spots with gray centers to form on the foliage. The spots may enlarge and eventually cause the entire leaf to wilt and die.
The disease can spread rapidly from plant to plant, significantly reducing yield and fruit quality. It is important to monitor your tomato plants regularly and take prompt action if you notice any disease symptoms. Early detection and treatment can help reduce the disease’s spread and prevent severe crop losses.
Septoria Leaf Spot Management in Tomato
The Causal Organism of Septoria Leaf Spot
Septoria lycopersici is the pathogen responsible for causing the Septoria leaf spot in tomato plants. The fungus thrives in moist conditions, so periods of high rainfall or overhead irrigation can increase the risk of infection. The fungus can also persist in plant debris and soil, making it important to practice good crop rotation and to remove and dispose of infected plant material to reduce the risk of future infections.
The Disease Cycle of Septoria Leaf Spot
- The disease cycle of the Septoria leaf spot starts when fungal fragments (conidia) are deposited onto and penetrate the leaves of tomato plants.
- The fungus can rapidly develop and spread when favorable environmental conditions, with abundant moisture and moderate temperatures.
- The pathogen can be dispersed through various means, including equipment, plant stakes, contaminated seed, insects, and workers. Rain splash and overhead irrigation can also contribute to the spread of the disease by spreading fungal fragments from one plant to another.
- The fungus can survive between tomato crops in infected plant debris, on solanaceous weeds, or on contaminated seeds, making it important to practice good crop rotation and to remove and dispose of infected plant material to reduce the risk of future infections.
Causes/conditions Favorable for Septoria Leaf Spot Disease Spread in the Field
- High humidity and warm temperatures can create ideal conditions for developing and spreading Septoria leaf spots caused by the fungus Septoria lycopersici.
- The fungus can overwinter on infected plant debris or nearby weed hosts. It can be spread by rain splash, wind, or contact with infected foliage.
- Overhead irrigation can also contribute to the spread of the disease by keeping the foliage moist, which provides a suitable environment for the fungus to thrive.
- By reducing the amount of overhead irrigation and removing and destroying infected plant debris, you can help to reduce the risk of the Septoria leaf spot and minimize its impact on your tomato crops.
Symptoms of Septoria Leaf Spot Disease
- The symptoms typically start as small brown spots, dark margins, and tan to gray centers on the lower leaves, which can quickly spread and cause defoliation of the plant.
- These spots are often dotted with black fungal fruiting bodies (pycnidia) and may be surrounded by a slight yellow halo. Stem, petiole, and calyx lesions are generally smaller and may or may not contain pycnidia.
- If the disease is severe, it can cause the leaves to turn yellow, brown, and wither, reducing yield and fruit quality.
- Fruit can also become sunscalded if the disease severely damages the foliage. To minim