Plant pests and diseases: lists and how to eliminate them

Plants are threatened by a large number of agents that can attack them, most of which are pests or diseases. These dangers are usually considered only when they affect crops or farms due to the significant economic losses that they can lead to, but almost all plants are susceptible to being attacked.

In this article we are going to give lists of the most common pests and diseases of plants , in addition to giving some guidelines on how to eliminate and prevent them . The most expert in gardening will recognize some of the names, but it is worth knowing as much as possible the dangers that our plants can face.

Most common pests of plants

Pests are caused by animals, usually insects, that feed on the plant or cause damage in some way. They are not all, but the following are the most common plant pests :

  • Aphids: they are very small insects, similar to grains of rice. The most common are green aphids , but there are more species, such as black, red, white or yellow aphids . They feed on plants by sipping their sap and can attack almost any plant. They excrete a honeydew that attracts ants, with which they maintain a symbiotic relationship, and that can also cause a fungus called Negrilla to appear. 
  • Mealybug: These other insects, shaped like a small shell, also feed on the sap of plants. They are usually located on the stems and the underside of the leaves, and they also excrete the excess sugar that they obtain from the sap in the form of wax. There are several types of mealybugs on plants , such as cottony and grooved mealybugs .
  • Red spider: small red or black mites , which also suck the juices from the plant, weakening it and making it vulnerable to other attacks from other pests or diseases, so if they are not treated in time the plants end up dying. They occur with high temperatures and when humidity is very low. When there are many of these spiders, they can produce visible cobwebs.
  • Weevils: this is another of the insect pests that feed on plants. They are also known as weevils or curculionids and there are many different species, such as the rice weevil, the wheat weevil or the corn weevil. 
  • Thrips: they are small winged insects that feed on the leaves and sometimes the fruits. They usually appear in spring, when most plants are in better health, with more leaves and fruits.
  • Whitefly: also known as aleurodids , they make up a large group of more than 1,500 species. They are one of the pests that cause the most damage to plants and crops.
  • Leaf miners: these are the larvae of various species of insects that develop inside plants, especially in the part of the leaves. When feeding on these, they cause serious damage to the plants and they can even die. They leave very characteristic marks on the leaves, which are like white paths.

Plant diseases – the most common

As with pests, there are countless diseases that affect plants of all kinds and around the world. The most common are the following:

  • Botrytis: also called gray rot , it is caused by a fungus ( Botrytis cinerea ) that produces a grayish mold on any part of the plant. It is usually caused by excess humidity.
  • Rust: This fungus causes small yellowish or brown spots and deformities to appear on the stems and leaves.
  • Mildew: it is a fungus that appears in conditions of high humidity and temperature. Mildew attacks plant leaves, causing dark, oily-looking spots.
  • Powdery mildew: it is very easy to identify by its appearance as a light-colored powder on the leaves, similar in appearance to ash. Powdery mildew is a disease caused by a fungus, and therefore must be treated with fungicides.
  • Anthracnose: it is a disease produced by fungi which is also known as chancre or canker . It produces brown spots on the leaves, especially around the main veins of these. 
  • Alternariosis: this fungal disease, also called negrón , affects the leaves and fruits of plants. It is recognized because it produces darker circular spots in the center and with circles or rings around a lighter brown or yellow tone.

Natural treatments for plant pests and diseases

There are many organic and natural substances that you can use to combat plant pests and diseases without resorting to chemicals.

  • A great insect repellent is garlic . A solution of crushed garlic with cloves in steamed water on the plants will keep many pests away.
  • Similarly, tomato leaves are a great repellent against aphids and worms, so spraying a solution of chopped leaves in water will work, but be careful with your pets, this mixture can be toxic to them.
  • The ground eggshells , in addition to fertilizing the soil, also scare away snails and slugs. 
  • Coriander boiled in water in a high concentration will kill most mites on plants.
  • Against mealybugs and aphids, on the other hand, vegetable oil is the best option, mixed with water and liquid soap .
  • Against fungi, a tablespoon of baking soda mixed with two liters of water spray once a day will be a great ally.

How to prevent pests and plant diseases naturally

Many of the remedies that we have given , such as egg shells and garlic, can be used preventively against a wide variety of pests, since they do not harm the soil and even enrich it.

Against fungi, on the other hand, the best preventive measure is always not to overdo the risks . An excess of humidity will provide an ideal environment in which to appear. Also, if you keep your plants pruned so that the air flows well between them and separated from each other, you will also make it very difficult for fungi to appear.

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