It is a fungus. A fungus that releases spores. The spores spread onto other leaves. The spores spread to other plants. The fungus is Alternaria Solani. It is one disease your tomatoes can get. The disease typically takes hold on the bottom leaves of tomatoes, typical when fruit first sets and humidity comes into the picture. It starts out as tiny brown spots on lower leaves. For My area, in Zone 7 Maryland, Early Blight shows about mid July when the humidity, as I mentioned, arrives.
The initial brown spots maybe hard to see at first. The spots turn yellow, grow and spread. The yellow spots might have a light brown/black/gray center of concentric rings. The spots are a good size once the yellow ring forms. The discolored center looks like dried leaf surrounded by a yellow ring. This yellow ring with a brown center is what you use to identify Early Blight.
|Early Blight - Concentric Brown Rings with Yellow Edges.|
The picture of my tomatoes, below, have some leaves with blight. It also shows the die back from determinate varieties like the one in the front and some plants just didn't do well with 95+ degree heat. The point is that it can be very hard to identify diseases like Early Blight, Leaf Spot and Late Blight from standard die back of leaves or other issues like ailments from nutrients. It is confusing. You should do a Google search for tomato disease pictures. It helps with identification.
|Some Early Blight Spots - The Rusted Garden Blog|
If left unmanaged the disease will travel up your plant and it can even damage the fruit. You will notice brown dots on the tomatoes if this happens. Eventually, the leaves die and drop off, leaving your fruit exposed to sun scalding. The plants weaken and often die or stop producing.
I wish the goal was total prevention of the Early Blight or any disease but I think a better goal is practicing good habits to manage down diseases and their damage. If you can manage diseases (yes hopefully prevent it) so it progresses slowly then your tomatoes can often out pace the spread of the disease with its own growth and production. My growing area is know for Early Blight. A lot depends on the climate. Some of you will never see it. Last year it was not only was kept in check, I didn't see much of it. I practice most of these 10 habits. I just don't always have the time or space to practice them all.
As mention Early Blight is a fungus. When the fungus gets wet and conditions are right, spores are released. The spores spread the fungus. The fungus is spread by splashing water, human contact, wind and even insects. The spores can travel distances through hands, tools, insects and wind.
Early Blight needs warm wet weather to spread and grow. If you have warm weather and moisture, your garden is at risk. Early Blight, once established in your garden, can over winter in your garden on debris and weeds.
Number One: Don't let it over winter!
You can't vacuum up the spores unfortunately. At the end of the season throw away, don't compost, all infected debris and surrounding debris. It is also important to pull up all the weeds in the beds as they take over in the Fall and early Winter period. Spores can over winter, as mentioned, on debris and weed hosts. You want to reduce the number of spores laying around in wait.
Number Two: Turn the soil in mid Winter.
The spores aren't super spores. Burying them into the earth helps remove them. Some people may not like to turn their garden in the Winter because it exposes the worms. I prefer to turn it because it also exposes snails and snail eggs. I figure the worms are plentiful in my area and I am only turning about 10 inches of the garden. The worms will survive and you can bury potential diseases that will die out in the earth.
Number Three: Create a soil barrier, also known as mulching.
Since Early Blight doesn't come right away, you have time to mulch and create a soil barrier. This is effective for many diseases in your garden. You can use newspaper, plastic, grass clipping or anything you wish. You want to create a splash barrier. Rain drops and over head watering, splash soil on to the tomato plants. That is one way to infect your plant. If you seal the soil then you will reduce the chances of spores finding your plant. I suggest using a layer of newspaper covered with mulch or grass clippings. Bottom line, you don't want your soil exposed to your plant.
|Mostly Healthy Green Leaves - The Rusted Garden Blog|
Number Four: Water from the bottom not the top!
The spores need moisture. Watering from the bottom prevents splashing as mentioned above, splashing is bad. Watering from the top of your plant makes for wet moist leaves and it creates a temporary humid micro climate. The moisture allows the fungus to produce spores. Dry leaves. Dry leaves. Dry leaves. I don't recommend watering in the evening. Let the sun be your friend and dry up the garden area. Night time watering lets the moisture sit all night. Dry leaves. Did I mention Dry leaves?
Number Five: Air circulation, plant staking and no touching.
Air circulation allows the wind to blow through your plants. This allows for the timely drying of leaves and it helps break up micro climates. If your plants are packed too tightly together, they themselves become barriers to drying. Staking your plants to poles and using cages helps them grow upright and it creates gaps between the tomato plants. You want to wind and sun to reach through and around your plants. Moisture is needed for Early Blight to spread. Dry is good. Staking and caging also keeps each plant from touching. The tomatoes should be planted with enough distance that only minor pruning is needed to keep them from touching each other.
Under Standing Soil Splash and Disease Prevention
Number Six: Remove 12-18 inches of bottom leaves and prune your plants.
Early Blight typically grabs hold on the bottom leaves first. I already mentioned soil barriers and watering from the bottom of the plants to prevent splashing. The next step is to create a 1-2 foot space (depending on the adult size of your tomato plant) between the garden soil or mulch and the first leaves of the tomato plant. Prune the bottom leaves from you plant, over time, as it grows, to create an 12 to 18 inch barrier gap. If the spores can't splash upwards and reach the leaves, they can't take hold. The stem usually isn't a place for the spores, though it can be. If you have large plants, you might consider cutting off some branches to let the sun and wind blow through the main body of your tomato plant.
Number Seven: After the tomatoes set add some nitrogen.
A healthy plant tends to fight off the spores. You don't want to add too much nitrogen to your tomatoes before they set fruit. Too much nitrogen before fruiting leads to more leaves and less fruit. The leaves are what the spores want. Once the fruit is set, a nitrogen boost can help strengthen your plant. This is a one shot deal. This tip would basically include keeping your tomatoes well nourished as to keep them strong.
Number Eight: Remove infected leaves immediately.
A leaf should be completely green. Remove leaves that show signs of disease immediately. Look for brown spots or yellow spots or distress. Keep in mind your hands and tools can spread spores. Take precautions not to spread the spores yourself. You should remove leaves and prune when it is dry and sunny. Wash your tools and hands often.
Number Nine: Spray the plants proactively.
There are a lot of products out there for Early Blight. I suggest checking them out and deciding what you are going to use. I use wettable sulfur. It creates an environment on the leaves the spores don't like. The key to spraying with wettable sulfur is to do it weekly before signs of the disease shows. Other products also help stop the spread. Whatever you select, the key is to spray early and regularly.
Number Ten: Rotate your crop.
I leave this tip for last because most of us do not have enough space to do this effectively. Because Early Blight also effects other plants, rotation in small gardens isn't practical or even possible. But if you have the room, move your tomatoes to plots that are free of Early Blight spores. You can find standard rotation plans on the internet. I wish I had more room to do this. A typically rotation schedule suggest 3 years away from a plot before returning the same crop.
I also suggest Number Eleven... water your plant with an aspirin. I have been reading that salicylic acid, in aspirin, triggers a defense response in tomatoes. It boost the immune system so to speak. Do a search on aspirin and tomatoes. It is interesting, I have been doing it several years and believe it greatly helps.
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