Plants can be affected by numerous parasites. This term often identifies insects, fungi or other plants capable of systematically or forever installing themselves on the affected plant to feed on it. Pests can affect any type of plant, from indoor to outdoor, outdoor or greenhouse crops and ornamental species. There are parasites that prefer certain plant species, others that affect any plant variety indiscriminately. The spread of plant pests it is favored by some environmental conditions, such as excessive humidity or increased temperature. For plants grown indoors, temperatures that are too high must always be avoided, while for those outdoors it is necessary to check that the plant has not suffered water stagnation. In phytopathology i plant parasites they are classified into insects, fungi and plant parasites. We are excluding from this classification viruses and bacteria that cause diseases, because indirectly and in some conditions, they can be carried by parasites.
There are many parasitic insects on plants, although those that frequently attack ornamental plants are aphids, spider mites, cochineals and whiteflies. Other pests capable of damaging plants are some species of beetles, such as Colorado beetle and beetle, ants, caterpillars and the grillot mole. Plant parasitic insects are also called phytophagous as they feed almost exclusively on the affected plants. The aphids, tiny insects with a fluorescent light green color and thin legs, feed on the sap of the leaves and buds, through their very pungent mouthparts. The excrements of their nutrition are formed by a sugary substance, called honeydew, which attracts other insects, such as ants, able to protect the aphids from other predators. Aphids, due to their shape, are also called "plant lice". The abundant production of honeydew is also able to cause a fungal disease called "fumaggine" in plants. The spider mite is a mite belonging to the arachnid class, the same as spiders. This pest always feeds on the leaves and buds of affected plants. The mouthparts are made up of pointed and small structures, the chelicerae, which serve to steal nourishment from the infested plant parts. The plant affected by the red spider appears covered with a thin spider web, the leaves can turn yellow and develop malformations or tissue hardening called "galls". The scale insects are small insects with a rounded back, which attack the leaves and branches by emitting a white and flaky substance capable of blocking the development of the plant. Mealybugs also produce honeydew. The same substance is also produced by whiteflies, insects similar to common flies, but smaller and white in color. These attack the leaves of plants and are oliphagous, that is, they prefer some species of plants, while they do not attack conifers. Ants attack the bark of plants, where they lay their eggs. This operation alters the tissue of the cortex by forming galls. Harmful for the leaves of the plants are the caterpillars, or the larvae of the butterflies, which feed on the leaves with a frightening voracity. The same damage is caused by snails. The grillotalpa is an insect clearly visible to the human eye that digs tunnels on the ground at night, feeding on the roots of plants. The beetle is a beetle that as an adult feeds on the leaves, while as a larva, on the roots. Colorado beetle is a beetle that feeds on the leaves of the potato, tomato and other solanaceae.
The parasitic fungi of plants are ascomycetes capable of causing diseases such as white sore, gray mold, scab, cancer, rust and downy mildew. Ascomycetes include several species of plant parasitic fungi that can settle in the host plant structure to feed and reproduce. Ascomycetes can reproduce sexually or asexually, even if their main organ of diffusion and propagation is represented by the spores containing the mycelium of the fungus and carried by the wind. The spores hide on the ground or under the leaves in the winter period, while they overwinter in spring or summer, when the temperatures rise and there is a strong humidity. The ascomycetes responsible for the white disease belong to the genus oidium, in fact, the disease is called powdery mildew, those responsible for the rust belong to the genus Puccinia, those that cause gray mold are called "Botrytis cinerea", while the fungi of downy mildew belong to the family of Pziziacee and to different genera that attack certain plant species: from grapevine to lettuce.
Plant parasites are fought with biological or chemical control. The first uses natural remedies as predators of parasitic insects. Among the predators of parasitic insects we also find ladybugs and hymenoptera (wasps). Some bird species can also be useful in eliminating certain infesting beetles. Other natural remedies are represented by organic substances with repellent effect on parasitic insects. Garlic can be used for aphids, while carrots and onion can be used for whiteflies. These vegetables must be chopped, macerated in water for 24 hours and then distributed, in the evening or early in the morning, on the infected parts of the plant. Fungal infections can be fought with specific fungicidal products, easily purchased in nurseries.