Tomato diseases due to excess moisture and treatment

Tomato plants are sensitive to excess moisture

Excess moisture is a problem for tomato plants. But it is not always easy to know when to water them, because they are plants that suffer a lot from drought, to the point that their stems lose their firmness as soon as the soil begins to be a little dry. For this reason, and in order to prevent them from becoming like this, we frequently pour water over them.

And, of course, if we go too far…pathogenic fungi and oomycetes will soon appear, those micro-organisms that will take advantage of the weakness of our crops to cause them to rot. So We are going to see what are the tomato diseases caused by excess humidity to know how to identify and treat them.


What are?

When we water too much, the tomato plants have a lot of trouble. But what are the diseases that can affect them when they have more water than they need? Basically, there are three: powdery mildew, mildew and botrytis or gray rot.

powdery mildew

Powdery mildew is a serious tomato disease

Image – Wikimedia/Goldlocki

Powdery mildew is a disease caused by various pathogenic fungi. They affect a multitude of plants, not just tomato plants, so it is important that where possible we separate those that are diseased from those that are healthy.

Symptoms appear on leaves and stemswhich are covered with a whitish powder which, if you touch it, will dirty your hands.


The affected parts must be removed by cutting them with previously disinfected scissors. Besides, A fungicide will be applied, if possible ecologicallike this ponytail you can buy here.


Downy mildew is a tomato disease

Image – Wikimedia/Rob Hille

Downy mildew is a fungal disease caused by oomycetes of the Peronosporaceae family. Like powdery mildew, it affects a wide variety of plants, both horticultural and ornamental. And also Excess humidity favors it, especially if the temperatures are high.

We will see the symptoms both in the leaves and stems and in the fruits. Small yellow spots appear first, which quickly turn gray.


These micro-organisms are fought with fungicides like the one we told you about previously, or with this other from the Solabiol brand that you have to dilute the contents of the sachet (50 grams) in 15 liters of water. Then fill a spray bottle with this mixture and spray the liquid on the plant.

Gray mold (botrytis)

Botrytis is a tomato disease

Image –

Gray rot is a disease caused by the fungus Botrytis cinerea. It affects many plants, especially vines, but also tomato plants.

How do we know if our cultures are suffering from it? The leaves will begin to become covered with a kind of white ash, and will die. In addition, the fruits will first have light brown spots, then they will rot.


To combat botrytis, systemic fungicides are used, such as the one from Probelte Jardín that you can buy here. Instructions for use are as follows:

  1. A 1 liter spray bottle should be filled with water.
  2. Pour 2 to 3 grams of fungicide into the sprayer and mix.
  3. Apply by foliar route, that is to say by spraying the leaves and fruits.

How to prevent tomato seedlings from getting sick from excess moisture?

Tomato plants are watered frequently

Image – Wikimedia/Forest & Kim Starr

We now know what the diseases of tomatoes are due to excess humidity, but how do you prevent them from getting sick? To do this, we explain below how to properly care for your plants. This way, you can minimize the risk of them ending up with a problem:

When to water tomato plants?

Irrigation is important for tomato crops because These are plants that need a lot of water., especially if they are in pots. It will therefore be necessary to water often, but avoiding excesses. The question is: when should they be watered?

It will depend on the weather and rainfall, but if we live in an area with little rain and high temperatures, we will need to water about 2 times a week in the spring and 3 to 5 times a week in the summer.

How to water tomato plants?

This will always be done by pouring the water on the ground. Plants should not be wet, otherwise they could get sick and/or burn if the sun hits them at this time. But otherwise, they can be watered with a watering can or by turning on the drip irrigation system.

This, yes, you have to pour water until you see that the earth is wet. If they are in containers, we water until they come out through their drainage holes, this way we will make sure that we water them well and that, therefore, they can hydrate without problems.

You have to be careful: the upper layer of the earth dries out quickly, which could lead us to believe that it needs to be moistened again. But, it is a mistake. Lower layers of soil take longer to dry outsince they are not exposed to the sun, so if we watered now our plants would probably get more water than they really need.

Must wait. If in doubt, we will take a thin wooden stick, we will introduce it at the bottom, and if when we withdraw it we see that it comes out practically clean, we will water it.

Hope this was helpful to you.

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