The spots that can be found on the leaves of plants are very varied and depending on their shape, color and position they can be due to fungi, insects, mites, viruses, bacteria, a nutritional factor or simply an environmental factor such as sun, rain, hail, wind… In today’s article we will see how to know if our plants are under attack and how to fight it.
The first thing we must observe is whether the origin of the spots is due to an infection or not, so if we see that the spots are irregular in shape on the plant and are gradually spreading, it means that they have an infectious origin but if we see the symptoms in general on all the leaves and we see that it will not go further, it would be a non-infectious problem.
Based on this fact, we can determine if the origin of the spots is from a virus, fungus, pest, lack of nutrients or an environmental factor. Being of viral origin if it spreads gradually throughout the plant or of non-infectious or non-viral origin if it is seen generally in the plant, then it is due to a lack of nutrients or an environmental factor like being very cold.
Brown spots on the leaves
There are many types of brown leaf spots that can be caused by insects, fungi, viruses, bacteria, or a lack of nutrients. It will not be easy to find out what affects the plant, but we will try to explain the most common cases.
We will first find out if the cause of the brown spots is infectious (caused by fungi, viruses…) or non-infectious (weather cause or lack of nutrients).
- infectious: This is when it is distributed irregularly throughout the plant.
- Non-infectious: The brown spots also affect the whole plant and do not evolve further.
Types of brown spots on the leaves according to their shape
Depending on the shape of the spots on the leaves, it can be one disease or another, so we will describe some shapes of the spots to make a better diagnosis.
Circular brown spots on the leaves
Circular lesions formed by fungi or viruses, an example may be fungus Cercospora beticola. The lesions do not affect the major leaf veins.
They are irregularly shaped spots that take the form of leaf veins. They can be caused by fungi like alternaria, corynespora or by bacteria like Xanthomonas
They look moist, oily, translucent…they can be found in leaves, fruits and stems and they spread easily. They can change color quickly, from brown to dark brown or black, and can be surrounded by a yellow circle.
These spots can also be caused by fungi such as mildew or alternaria. Or they can be caused by bacteria such as Pseudomonas.
Extended and extended spots
It may happen that the disease is so widespread that the spots join together and can be one of the previously described. They can be caused by bacteria, fungi such as botrytis, midiu, sclerotin…
tree ring stains
When we look at these spots, we can see concentric lines inside them similar to those seen on trees that have been felled. They are due to diseases caused by fungi in a very advanced state.
Once we have detected the possible cause, we proceed with the treatment if it has a solution, because in the case of viruses and certain bacteria, there is not much we can do except prevent their spread.
White spots on plant leaves
As for the white spots on the leaves, they can also be caused by different diseases or pests that we will see below:
One of the main causes of white spots on the leaves is the powdery mildew fungus as it is very easy to cause to appear. It can affect a wide variety of crops such as melon, watermelon, pumpkin, zucchini, cucumber, tomato, beans, potatoes and others devastate life. White spots appear that gradually turn grayish.
Normally it is located on the upper part of the leaf and if we do not control it in time, it can end up drying out. In addition, its ideal conditions are heat and humidity, if there is any in your garden, it is most likely powdery mildew. It is a fungus that, if detected in time, can be eliminated, with treatment with milk or sulfur, it is also recommended to remove the affected leaves.
It affects most horticultural and fruit crops outdoors or in greenhouses. White spots turning gray appear on fruits and stems, spreading in such a way that they can cover them completely if not controlled in time. It can also affect the leaves but this is only in exceptions. It can be fought with milk treatment or biological control with trichodex.
This mite likes humidity and high temperatures, so if it has spread a lot, it generates whitish micro dots on the leaves. It can affect horticultural crops such as potatoes, beans or strawberries and ornamental plants. They are located on the underside of the leaves, they are visible to the naked eye, very small red dots, and the bites are also very easy to identify. It can be easily fought.
Some sort of galleries are usually observed in the upper part of the leaves and one of the best ways to control them is to pull the leaves where they are observed and throw them away from the orchard.
Tuta or tomato moth
Translucent or whitish spots are usually observed in the tomato, it is nothing more than the gallery of the tuta. It can be fought in many ways, but the easiest is with Bacillus.
Yellow spots on the leaves
Yellow spots on the leaves can be caused by many factors, as we mentioned before, we are going to know the most common ones.
yellow and green stain
The main symptom of having viruses is yellow spots on the leaves. In the form of mosaics, yellow spots that turn greenish, curled leaves and even dwarfism in crops. They can affect any crop but especially vegetables.
Worst of all is that the viruses have no solution, the plants must be uprooted and thrown away so that they do not affect future crops and prevent their expansion. An example is tomato mosaic virus.
Yellow leaves due to lack of nutrients
There are many types of deficiencies, but those that produce yellow spots or chlorosis are due to a lack of nitrogen, phosphorus, magnesium, iron or manganese.
If chlorosis appears on young shoots and leaves, the deficiency will be iron or manganese (micronutrients), but if it occurs on older leaves, it will be due to a lack of nitrogen or magnesium (macronutrients). The best way to solve this problem is to fertilize the soil with nutrient-rich compost or worm castings or nitrogen-rich fertilizers.
Yellow spots on the leaves due to fungus
The yellow spots produced on the leaves can also be due to mold or rust. Mildew can affect crops such as vines or nightshades, while rust affects leeks, garlic, onions… Over time, the yellow spots will turn brown.
One way to identify if we have the fungus on our plant is to observe the underside of the leaves, if we see in the case of downy mildew that there are whitish spots on the underside, it is this fungus. In the rust, we would see orange spots.
Yellow spots caused by parasites such as whitefly or red spider mite
These pests have biting mouthparts because they are phytophagous species (they feed on plant sap). We can see on the leaves, some small yellow cores.
Yellow leaves caused by nematodes
Leaves can turn yellow as nematodes produce nodules on plant roots, rendering them unable to properly capture nutrients. What to do if there are nematodes?
Lack of humidity
It produces yellow spots on the edges of the leaves, even wilting.
Black spots on the leaves
The presence of black spots on the leaves can be due to fungi present in the plant but also to other causes that we will see below.
natural leaf death
Leaves don’t live forever, even those that never fall to the ground have a while to live.
The black spots on the leaves can be caused by plants that have been sprayed with water in the middle of the day because the burl effect occurs and burns the leaves or it can be due to a plant that we we have inside the house or greenhouse and we put it in direct sunlight, not being used to it burning.
When there is heat and excessive humidity, fungi can appear that leave black spots on the leaves such as mildew, powdery mildew, rust or anthracnose. The spots may have a different color at first, but as the disease progresses they turn black.
Plants may have poor drainage due to the type of more clay soil or excess water in irrigation, these are some of the factors for the appearance of leaves with black spots.
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