Septoria leaf spot, also known as Septoria blight, is a widespread disease that commonly attacks tomatoes. It can be incredibly destructive and, in severe cases, can lead to 100% crop losses. But there are ways to avoid or at least minimize attacks.
The best way to deal with the Septoria leaf spot is to take early steps to minimize the possibility of it occurring in the first place. When tomato plants stop producing, you should remove and destroy all tomato debris. Then be sure to plant healthy seedlings that are 100% disease free.
What is Septoria Leaf Spot?
Septoria leaf spot is a fungal disease caused by Septoria lycopersici. It is mainly a disease that attacks tomatoes but sometimes affects other Solanaceae, or nightshade plants including potatoes, eggplants, petunias, and some weeds.
It usually appears on the older, lower leaves and stems of established plants setting tomato fruit. Usually, the first symptoms appear on the leaves, but they may also occur on stems, petioles, and the calyx, which is the flower-shaped leaf on top of the fruit.
The fungus attacks when conditions are warm, humid, and/or wet. It is particularly severe in regions where this kind of weather persists for extended periods.
Septoria leaf spot overwinters on tomato debris that has been infected as well as on weeds in the nightshade family. It can also survive on plant stakes, tomato cages, and other equipment.
Symptoms to Look Out For
The fungal spores that cause Septoria leaf spots germinate very quickly, and in only about 5 days you will start to see spots. The quicker you identify them, the more success you are likely to have to slow down the spread of the disease.
You need to look out for small, water-soaked, round spots that are between 1/4 and 1/16th of an inch in diameter. The centers of these spots are usually a tan to a gray color with a dark brown outline.
The spots cause lesions and you will soon see very small black spots. These are tiny fungal fruiting bodies called black pycnidia.
If left untreated, the leaves will turn yellow, then brown as they wither and die.
Can you cure leaf septoria?
Unfortunately, Septoria leaf spot on tomato leaves is incurable.
How do you treat septoria leaf spots on tomatoes?
A major challenge is that the Septoria leaf spot often recurs annually. There are fungicidal sprays that you can use to treat the disease, you need to use them as soon as the spots start to occur to slow down the spread of the disease.
These are worth considering since the fungicide will protect new leaves from infection. You can use a synthetic fungicide or an organic product that contains copper. Apply early in the growing season, according to the directions on the product label.
An important caveat is that these products are seldom effective if tomato growers don’t combine them with proven management tactics.
How do you prevent septoria leaf spots on tomatoes
The best way to prevent the Septoria leaf spots from forming on tomato plants is to introduce what the experts call cultural techniques to limit the disease.
The University of Maryland Extension has some useful tips to manage the Septoria leaf spot.
First and foremost, you need to make sure that there is sufficient space for air circulation between your tomato plants. Remove any suckers that grow up from the base of the plant.
Be sure to keep an eye out for any signs of the disease. Once the plants are established and begin to produce fruit, prune the lowest 3 or 4 leaf branches.
When you water your tomatoes, water at the base of the plants and avoid getting the leaves wet. Never water overhead.
You can also use a soaker hose to water. Drip irrigation also works.
Keep the soil well mulched to minimize water splashing off the soil.
It is good practice to cut off infected leaves during the growing season and to remove all infected plants when the season ends. Shred the diseased plant parts and dispose of them.
It is acceptable to compost the shredded parts IF you use hot composting methods. But it’s important that the pile temperatures are constantly higher than 120 ℉, and you must turn the pile regularly.
Unless you have experience, it’s best not to compost any infected tomato debris.
Other management tactics suggested by the Missouri Botanical Garden include staking or caging plants to raise them off the ground. This also allows tomato leaves to dry more quickly after rainy weather.
It is also important to control the weeds that typically act as hosts of Septoria leaf spots. These include horsenettle and nightshade.
They strongly suggest using crop rotation especially if your tomatoes have been affected by leaf spots. Rather wait 1-2 years before replanting tomatoes or any other nightshade plants (Solanaceae) in these parts of your veggie garden.
Lina Rodriquez Salamance, an extension plant pathologist and diagnostician at the Iowa State University Extension and Outreach suggest a longer rotation period. She says it’s best to rotate every 3-4 years to break the disease cycle.
Can I eat tomatoes with septoria leaf spot?
Septoria rarely affects the tomato fruit. However, if most of the tomato leaves are infected, this can weaken the plant and expose the fruit to sunscald.
If the fruit is intact, the only thing to beware of is the residue of fungicidal sprays. Take note of all safety precautions listed on labels particularly harvest restrictions.
Septoria leaf spot is a common, very widespread, and destructive fungal disease that attacks tomato plants. It cannot be cured, but there are ways that you can deal with it.
Also, since it doesn’t usually affect the tomato fruit, it won’t impact your crop. At the same time, there is no doubt that the disease can create a major challenge, especially when it recurs.
Understanding its characteristics and management methods will help you protect your tomato plants from the Septoria leaf spots. Knowing what to expect will also help you deal with the disease when you are faced with infected leaves.