2017 Harvest

Tuesday, July 15, 2014

Tomato Blights and Septoria leaf spot

Every gardener that grows tomatoes will sooner or later come across a stage when his tomatoes will look sick, spotty, black or yellow. There are many different tomato diseases and different causes. This time of the year the most common diseases are fungal diseases so I bring you list of 3 most common and how to identify them and treat them.

                                                      1. Early blight(crna pjegavost)

Early blight is fungal disease caused by fungus called Alternaria solani. It affects tomatoes, peppers and blue aubergine. This type of fungus affects seedlings and older plants. It can be in the soil, seeds, leftover plants from past year, tomato poles and seedlings you buy in the store.
Early blight is know for it's brown to black spots that have concentric rings. It can occur on leaves, stems and fruits.
It's concentric rings are also called bull's eye and it's easily recognized.

Photo from http://ceventura.ucanr.edu/

Early blight can come at any time. It usually appears on plants that are stressed in some way. It prefers cold and rainy weather but it can start even on seedlings that are grown in greenhouses. When they affect seedlings they affect upper leaves. With older plants it's the other way around. Disease always starts on the bottom leaves and then climbs up. Another characteristic of early blight is that when affecting stems it first starts as a concentric ring around one part of the stem and then starts spreading up. Upper part of the plant will soon witter but lower part of the stem usually stays healthy.
Fruits can also be affected. They concentric black rings that are firm at the beginning and then the place of the ring rots. Fruits affected with early blight can still ripe. If they do they will have brown hard rings on them but the rest of the fruit will be ok. Fruits can still be used for cooking.Early blight is easily confused with much more serious disease called late blight.

                                                     2. Late blight (plamenjača)

Late blight is disease caused by fungus called Phytophthora infestans. It's a very aggressive disease that affects only tomatoes and potatoes. If there is large concentration of sick plants in the garden it is possible other plants like cucumbers and zucchinis will get infected too. It spreads very quickly and can devastate plants in just 2-3 days. Late blight always comes after bad weather condition. After heavy rains, floods and cold dewy mornings.
Spores are air born so the infection doesn't have to start in your garden. It can travel for miles and miles.

Late blight on potatoes
Classic late blight symptoms are olive green to brown spots on leaves or stems. After heavy rain leaves can cause border of the leaves to be yellow. As the disease spreads whole leaf will turn yellow and leaves will dry in the end.

Late blight on tomatoes
Late blight leaves yellow from dampness

Stems can also be affected. First there will be brown spots on them similar to mold that grows on house walls and then it will spread turning whole stem black. Once the stem is affected leaves and fruits will starve from lack of food and the whole plant will eventually die.
Fruits affected with late blight have large irregular greasy grey-brown spots and they literally start rotting. Once late blight attacks fruits they will turn black and if they are still red they will not ripe.

                                                3. Septoria leaf spot (Pjegavost rajčice)

Leaf spot is caused by fungus Septoria lycopersici. It affects mostly tomatoes all around the world. It can come at any time and any stage of the plant. It usually prefers the time when plants start producing fruits.
Leaf spots makes many small round spots(much smaller then blight). Center of the spot is grey and the other parts of the leaf are in shades of yellow. Once the spot matures it turns in brown pimple like mass on top of the leaf.

Photo from http://www.ipm.iastate.edu/

It affects lower leaves first and work their way up the stem. Fruits are almost never affected but since they damage stems and leaves fruits usually stay small like they were at the beginning of attack. Also since it attacks leaves plant it causes them to fall off so fruits get sunscald.


1) Rotate tomato crops:
Tomatoes should be planted on different bed every year. It would be ideal if the beds were on 4 year rotation. Tomatoes that are planted on the bed this year shouldn't go on the same bed in the next 3 years. 4th year tomatoes came on this years bed. This method requires a lot of room and planing so most gardeners can't do this.

If 4 year rotation is not possible then use 2 year rotation(tomatoes planted this year go on this years bed in 2016. If you can't rotate your crops then make sure you remove all plant debris (including roots) from this years bed.

2)Whitewash your tomato poles
Whitewash is great disinfectant. Early blight can stay on the poles so it's important that after you notice early blight this year you disinfect your poles for next year. It would be ideal to whitewash your wooden poles every year. If not possible every 2 years. If you use branches use new branches every year. If you use plastic poles wash them with some kind of disinfectant.

3) Place black plastic on the soil under your plants
Apart from being a great weed control black plastic can prevent blight and septoria from infecting leaves that are on the ground. Be careful with this method. If the soil is too damp tomato roots can rot under the plastic.

4)Fertilize your beds
Tomatoes love fertilized beds. Unlike carrots that shouldn't go on the bed that was recently fertilized, tomatoes should always be planted on fertilized bed. You can choose your type of fertilizer. I can recommend placing some manure(rabbit, cow, horse) in the hole made for seedlings. This ways they take what they need through the roots and feed whole plant.
Always use at least 2 years old manure. Manure that was collected the same year can be too strong and damage seedlings.

5)Water only the soil
When watering be careful to water the plant close to the ground. This way you can prevent wetting lower leaves.

6) Spray your plants with Bordeaux mixture 
Bordeaux mixture is a great fungus prevention. It can protect your plants from fungus. But it can only prevent them. Once the plant gets infected and starts showing signs of disease mixture doesn't work. Also be careful not to spray after the plant starts producing flowers.

Homemade Bordeaux mixture: 10 liters of water
                                               400g of quicklime(burnt lime)
                                               100g of blue vitriol
In a bucket pour 5 liters of water and place inside a tied gauze with 100g of blue vitriol. Leave it for 24 hours and then remove the gauze. In this 24h vitriol will dissolve in the water and the remaining filth will stay inside the gauze.
In other bucket pour 5 liters of water and dissolve 400g of quicklime. After dissolving quicklime mix it with vitriol water. Use it right away. If you need to store it add 1dcl of boiled milk or 1dag of sugar and mixture can be stored for 14 days.

7)Fertilize with nettle
Once your plants get big you can fertilize them with nettle. Be careful not to make too strong mixture. This mixture is used to water the roots. Not spraying on leaves.

Nettle fertilizer:
Place 1kg of fresh nettle or 150g of dried nettle in a 10 liter bucket. Add water and leave it for 24 hours. The next day boil for 30 minuted the nettle water and cool it down. For watering use 1:5 ratio. 1 liter of fertilizer on 5 liters of water.

8)Spray with milk or baking soda
Milk and baking soda leave alkaline residue that can prevent fungus from growing.

Milk spray: Use skim milk in 1:10 ratio

Baking soda spray: Add 1 tablespoon to 1 liter of warm water, stir and add few drops of liquid soap and 2 tablespoons of vegetable oil. Spray your plants in evening to prevent sunburns on leaves.
Don't use it too often. Too much baking soda can damage the plant.


1) Keep an eye of your plants
Once the plants are already infected it only depends of the state in which you noticed the disease. If you notice it soon enough you can stop the diseases.
Fungal diseases can't be cured without fungicides.You can only stop them from spreading more. Once the leaf or stem is infected it can't be cured.

2) Cut down all the sick leaves
 If the disease is already here cut the sick leaves of the plant. They will only help fungus to spread. If the plant is infected also remove all leaves that look strange(have yellow borders, dried leaves...). Leave only healthy leaves. You can also remove sick stems if there is only one sick stem and other stems are healthy.
Stems affected with early blight can be cut few cm under the ring. The lower part will produce new healthy branches.

3)Remove all lower branches
Late blight usually starts from the bottom. If the plant is infected remove every branch under the ones that have fruits.

 That way there will be no leaves touching the ground and possibilities of new infections are smaller. You can also prune your tomatoes to remove all unnecessary branches from your plant. More about pruning read here  and here.

4)Try baking soda spray
Baking soda spray can sometimes help to stop blight and septoria from spreading. After removing all the sick leaves and branches you can spray with baking soda to prevent fungus from spreading.
If the diseases already affected stems there is very little chances baking soda will help.

5)Spray your plants
Here comes the unpopular part we all try to avoid. Once the plants are seriously affected there is not much you can do but spray them with some kind of fungicide.

Organic gardeners can use some of the copper based products and Bacillus Subtilis sprays. Watch for the waiting time and apply according to the directions on the box.

Non organic gardeners have more options for spraying. The most popular fungicides for blight and Septoria are:
1) Chorothalonil-Synthetic fungicide that has very short waiting time and it's good for spraying when plants already have fruits that ripe.

2) Copper based fungicide- There are many different types and combinations of copper based fungicides. Some of them are organic. Some of them are not. And some have very long waiting time. Choose wisely the one you need. Copper based fungicides can be used only 3 times.

3) Zinc based fungicides- The most popular is Mancozeb. This spray is only preventive. It can't help already sick plant.

4) Maneb- Synthetic fungicide that is only for already sick plants. It can't be used for prevention.

This are only active substances for fungicides. Every country has different name for products. Also be careful when buying fungicides. Every company makes different concentration of active substances so ratio that works for one product doesn't mean it will be good for other product. Too strong fungicide can burn your whole plant.
Always spray when there is no sun, always read the instructions and always watch for waiting time.


  1. Blight was the reason we stopped growing tomatoes outdoors,

    1. We had blight over the years but always in September and never so strong.

    2. It hit us in June this year which is early for us!

  2. Thanks for sharing this great information. Blight always be a nightmare for my tomatoes, pepper and brassicas.

    1. We don't have it as much on peppers and brassicas. Always only on tomatoes and potatoes.

  3. This post is very interesting, unfortunately, I'm familiar with these diseases, thanks for the tips how to deal with it, I've never heard about spraying with baking soda.

    I'm spraying preventively with water solution of calcium acecate (solution of calcium carbonate mixed with apple vinegar) and water solution of alcohol extract of thyme and oregano - interchangeably every 7-10 days. So far I had a few symptoms of early blight and late blight on tomatoes, but I cut down all infected leaves and sprayed the plants. It seems that the diseases have stopped.

    1. I heard that calcium acetate is good for Powdery mildew, but I didn't know it's good for blight too. Never heard of thyme and oregano. I'll have to try it.

    2. Thymol and carvacrol which are inredients of thyme and oregano act as disinfectant, they can kill some strains of bacteria and fungi. Later, I will write you the recipe for these sprays so you could try by yourself :)

    3. The recipes are not mine, I'm only using them :)


      You need:
      - 40 grams dried oregano
      - 40 grams dried thyme
      - 0,5 litre clean white 40% vodka
      - 1 litre water

      1. Take 1,5 litre bottle, put into it 40 grams of oregano and 40 grams of thyme.
      2. Pour 0,5 litre of clean white vodka and 0,5 litre of cold, boiled water over it.
      3. Put it away for 24 hours, stir it from time to time. Keep in a room temp.
      4. Next day drain the mixture, press the herbs thoroughly.
      5. Then pour 0,5 l of boiling water over the pressed herbs and leave under cover until it cools down completely.
      6. After that, drain again and mix water extract with alcohol extract.

      7. Use 150 mililitres of this mixture per 2-3 litres of spray. Use every 7-10 days.

      This herbal spray removes fungi from plants. It acts superficial, so it's important to cover all the leaves.

      When you add more than 150ml, let's say 150 or 200% of extract - it should be deadly for some species of aphids and other pests (I didn't try with snails and slugs).


      You need:
      - calcium carbonate (I use chalk)
      - 6 % apple vinegar or 10% synthetic vinegar
      - water

      1. Put 130 grams of chalk into 1 litre bottle and fill it up with water. <-- chalk suspension

      2. Take 5 litre bottle, pour 250 mililitres of 6% apple vinegar or 150 ml of 10% synthetic vinegar.
      3. Then pour 100 ml of chalk suspension (stir the suspension before adding it).
      4. You should get a chemical reaction with CO2 (carbon dioxide) liberating. There should be bubbles and a froth.
      5. After the reaction stops - fill the 5 litre bottle up with water.
      Spray plants every 7-10 days.

      It acts superficial, so it's important to cover all the leaves.


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