Plants can become sick for many reasons, but it is rare for them to die suddenly from disease. Generally, they become progressively weaker; therefore, they can almost always be cured if we know the symptoms to diagnose and know how to choose the right remedy.
Parasitic diseases are caused by microscopic animals that live and develop inside plants, feeding only on the substances produced by them. Inappropriate environmental or climatic conditions favour the proliferation of most parasites.
They are mainly spread and transmitted by sucking insects (aphids, thrips, mealybugs), which suck the sap from infested plants and also from healthy plants. They are also spread mechanically via the sap (by digging, cutting flowers, collecting, cutting, grafting, sowing, etc.) and also, although to a lesser extent, can be transmitted via the soil.
Viruses seriously damage ornamental, fruit and vegetable crops. They live in the cells of the plants, and the symptoms to recognize the disease vary according to the nature of the virus and according to the species or contaminated variety.
Among the most frequent symptoms are
- Irregular whitish or yellowish spots on leaves and stems. They are given the generic name of ‘mosaics’. One of the most common is the cucumber mosaic virus, which attacks various vegetables and numerous ornamental plants (petunias, dragon, aguileña, lilies, dahlias, pansies, primroses, etc.)
- Necrotic stains on the leaves, which cause tissue deformation This is a group of viruses that affects a multitude of plants (elder, petunias, almortas, etc.).
- Colored spots on the leaves of tulips, which result from the action of Tulipa virus 1 and Tulipa virus 2. It is a disease that produces a progressive degeneration of plants and affects not only tulips, but many others, such as pansies and lilies.
- Appearance of green inflorescences, accompanied by deformations or sterility of the flowering. They can be caused by viruses of the Stolbur group (especially in potato and tomato plants).
- Pale green or yellow blotches on the leaves and fruit, with wrinkled skin and reddish-brown flesh. It affects plums in particular; it is a viral disease called sharka.
They are caused by fungi, tiny parasites that are not visible and that feed on substances produced by vegetation. They are very serious diseases that can rarely be remedied when the first symptoms are observed and almost always cause the death of the plants. It is therefore essential to prevent the disease before it appears.
Bacteria live in the soil or inside infected plants. They mainly attack crops that have wounds or plants that are weak because they are grown in poor conditions. Control consists of preventing the disease or limiting it locally, adopting optimal growing conditions, eliminating infected parts, properly rotating crops, disinfecting the soil and combating crawling parasites, larvae and other animals that attack the roots.
They are divided into different categories, according to the symptoms that appear in the plants:
- Decomposition of soft tissues, full of sap. Wet or dry rot appears. In general they are caused by bacteria of the psedomonas and Erwinia families.
- Stains on leaves and other organs. They are usually caused by bacteria of the pseudomonas family.
- Appearance of systemic diseases. Usually caused by Xanthomonas.
- Plant cancers and neck tumors; usually caused by Agrobacterium tumefaciens.