Yellow Spots on Plant Leaves: Causes and Ecological Solutions

You may have detected in some of your vegetables yellow spots on the leaves or chlorosis. Below I will tell you what can be the causes of yellow spots and how to solve this problem with ecological and environmentally friendly methods.

Symptoms of plant problems, such as the appearance of yellow leaves, can be due to a wide variety of causes: pest damage, diseases (bacteria, fungi, viruses…), substrate problems, such as lack of nutrients or excess salinity, or even plant imbalances due to environmental conditions (light, pH, humidity…).

Causes of yellow spots on plant leaves

Detecting the cause of yellow spots on leaves is the first step in combating the problem.

I recommend that you analyze the different causes of this symptom and, depending on the crop in which the yellow spots have appeared on the leaves, the type of spots and the specific conditions of your orchard, discard them until you find what is probably the cause of the yellow leaves.

Yellow and green leaf spots caused by viruses

The main symptom of the presence of viruses in plants is yellow spots on the leaves. Alterations in the shape and color of leaflets appear. Areas of yellow and light green color (chlorosis) alternate on the leaves with other areas of normal green and dark green color (the so-called mosaics). The leaves are deformed, curling, curling or with a filiform appearance.

The worst thing that could happen to you is that this is the cause of the yellow spots on your plants, because diseases caused by viruses have no solution. You will not be able to use an effective organic treatment, so you will have to remove the plants as soon as possible to prevent the problem from spreading.

There are two very effective ecological methods to disinfect the soil in case your plants have been affected by viruses or nematodes. These are solarization and biosolarization. 

Yellow leaves due to lack of nutrients

Nutrient deficiencies produce symptoms on leaves and fruits, such as necrosis (black dead tissue), shriveling or yellowing.

There can be many types of deficiencies, but the main ones that produce yellow leaves or chlorosis are those of nitrogen, phosphorus, magnesium, iron or manganese. In this link you can see more details about the symptoms of nutrient deficiencies, such as the common yellow spots.

If chlorosis or yellowing of leaves appears first on new leaves and shoots, the deficiency is probably of micronutrients (iron, manganese…). On the contrary, if yellow spots are abundant on old leaves (those at the bottom), macronutrients such as nitrogen, phosphorus or magnesium are likely deficiencies.

This is quite an extensive topic so we will deal with it in more depth in other blog posts. For now, I refer you to this article where you can learn a lot about deficiencies, why they occur, what are the symptoms of each of them and how you can solve it: Mineral nutrient deficiencies.

The main solution to solve the problem of leaves with yellow spots due to lack of nutrients is, as it is logical, the fertilization of the soil for the contribution of nutrients. You can see more about the fertilization of plants in the post 5 ways to fertilize the organic garden. 

Yellow spots on leaves caused by fungi

Yellow spots on leaves can also be due to mildew (a fungus that usually affects vines and solanaceous plants such as tomato, potato, eggplant, bell pepper…) or to rust (more common in leguminous plants, in liliaceous plants such as garlic, onion, leek, asparagus, etc. or in ornamentals such as roses). As time goes by, the yellow spots will turn brown and will end up drying out if action is not taken in time.

These fungi can also produce other symptoms that will help you to detect them more accurately. For example, when there are yellow spots on the upper side of the leaves caused by fungi, you can also see a different coloration on the underside (whitish powder, in the case of midiu, or black or reddish spots, like pustules, in the case of rust).

You can find more information about fungal diseases in the entry Fungi in the orchard. If the yellow spots on the leaves of your plants are caused by fungi, organic fungicides will be very useful to fight them.

Yellow spots on leaves caused by whitefly or red spider mite pests

Whitefly or mite pests such as the red spider mite or the white spider mite feed on plant sap thanks to their biting-sucking mouthparts that bite the leaves.

These insect bites leave small yellow spots on the leaves and cause expensive spots to appear around them until the whole leaf is light green or yellowish and begins to dry.

To fight against these pests, if you do not want to use artificial or synthetic products but want an ecological and chemical free garden, you can apply some of these natural or ecological insecticides.

Yellow leaves due to nematodes

Nematodes also produce this symptom on leaves. Although the main nematodes are the nodules on the roots, these nodules or protuberances prevent the plant from absorbing water and nutrients properly and this also affects the leaves.

The consequence of this is that the leaves wilt and turn yellow. More information about this in the post Nematodes: what they are and what to do if they cause diseases in the orchard.

Leaves with yellow edges due to lack of humidity

Lack of humidity produces yellow spots on the edges of the leaves, which may even wilt. Other symptoms of this problem are brown tones on the tips or leaf drop.