Septoria Leaf Canker – Information On Controlling Septoria Leaf Spot On Tomatoes

by johnah on November 7, 2020

Septoria Leaf Canker (Leaf Spot) On Tomatoes: What Is It?

The Septora Leaf Canker (Leaf Spot) is a fungal disease which affects tomato plants. It causes leaves to turn yellow and fall off prematurely. Leaves may become discolored or even drop completely from the plant. Leaves are usually affected first, followed by fruit, stems and roots. The disease spreads quickly through the plant, so it’s very difficult to control.

What Causes Septoria Leaf Canker?

There are several factors that cause the disease. Some of them include:

Temperature: Hot temperatures promote infection because they encourage photosynthesis and produce sugars that feed fungus. Cold temperatures inhibit growth, but not enough to stop the spread of infection. If left unchecked, leaf spot will eventually kill your plants!

Light: Bright light encourages the growth of fungi, while dim lighting inhibits it. When the temperature is warm, sunlight stimulates growth and when it’s cold, darkness prevents infection.

Watering: Too much water promotes growth of mold spores and too little kills off infected plants. Watering too frequently during hot weather encourages infection while watering too infrequently during cool weather discourages it.

Conditions:Warm temperatures and bright sunlight encourage growth and prevent the plant from drying out. Moisture on the leaves also promotes infection.

How Do You Get It?

You have to get the spores of the fungus on your plant before it can take root and grow. This can happen in several ways:

Harvesting: In most cases, infected plants are harvested early because of leaf spots. It’s also common to harvest just part of the plant so that the rest can remain healthy. If you do this, it’s likely that plants will rub against each other, transferring the mold from infected leaves to healthy ones. This is especially true if the infected leaves are piled together.

Insects:Bugs such as grasshoppers and some species of caterpillar are known to carry the disease. They feed on infected plants and then go on to feed on healthy ones. If you grow plants in a field, the mold spreads like wildfire!

Rain: Heavy rain spreads the mold all over the place. It’s especially common to get infected soil from the farm next door.

Manure or Compost:This is a big one. Fungus from infected manure or compost can travel easily to your plants. If grown in large fields, it’s almost impossible to avoid.

Getting Rid of It

A lot of gardeners are unfazed by leaf spot and won’t take preventative measures to get rid of it.

Their argument is that some leaf spot is bound to show up anyway, so why not let nature take its course?

Not Me! I find it unsightly and prefer to grow beautiful tomatoes that don’t have spots all over them. Plus, leaf spot may prevent the fruit from ripening correctly or at all!

There are various ways to prevent and get rid of the fungus. Once it takes root it’s more difficult to eliminate, but there are some things you can do.

Here are some tips:

Rotate Crops: Don’t grow tomatoes in the same place two years in a row. Leaf spot tends to overwinter in the soil and can lie dormant until the conditions are right. Move your plants so the fungus has less of a chance to survive.

Don’t Grow Leafy Veggies:Leafy vegetables such as lettuce, spinach, and other greens are more susceptible to the fungus than others. If you’re growing leafy greens, it’s more likely that leaf spot will show up in your tomatoes.

Frequent Watering:Watering plants well and keeping them moist will help to prevent infection. This is especially true in hot weather.

Cover Crops:Include fast growing plants in your garden rotation. Cover crops such as lettuce and buckwheat will naturally die off and add organic matter to the soil. They also tend to draw leaf spot away from your main crop.

Keep Weeds Down:Weeds around your plants act like a reservoir for the fungus, if you keep them down it’s harder for the fungus to spread.

Sources & references used in this article:

Tomato diseases and disorders by ML Gleason, BA Edmunds – 2005 –

Reduction of incidence and severity of Septoria lycopersici leaf spot of tomato with bacteria and yeasts by LEB Blum – Ciência Rural, 2000 – SciELO Brasil

Evaluation of the Tom-Cast model for prediction of early blight, septoria leaf spot and anthracnose fruit rot in processing tomatoes in south-eastern Australia by EJ Minchinton, M Warren, A Watson… – … the Processing Tomato …, 2004 –

Directional spread of Septoria leaf spot in tomato rows by SK Parker, FW Nutter Jr, ML Gleason – Plant disease, 1997 – Am Phytopath Society

Effect of captafol and ridomil (R) Mz in the control of late blight (Phytophthora infestans) and septoria leaf spot (Septoria lycopersici) on tomato by T Tedla – X African Symposium on Horticultural Crops 158, 1984 –

Induction of Systemic Resistance by Bacillus cereus Against Tomato Foliar Diseases Under Field Conditions by HSA Silva, RS Romeiro, R Carrer Filho… – Journal of …, 2004 – Wiley Online Library



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