Introduction

Plant diseases can have either abiotic or biotic causes. While abiotic diseases are caused by environmental influences such as temperature extremes, excess or lack of wather or lack or excess of nutrients, the cause of biotic diseases, which are dealt with in this module, lies within pathogens (Greek pathos = suffering, disease). Pathogens are divided into the groups of pseudofungi and fungi, bacteria including phytoplasmas (cell wall-free bacteria) and viruses.

Diseases caused by fungi (Greek myces = fungus) and pseudofungi are called mycoses and pseudomycoses. They are controlled by fungicides (Latin fungus = fungus). Diseases caused by bacteria or phytoplasmas are called bacterioses or phytoplasmoses. They are controlled with bactericides.

Diseases caused by viruses are called viroses. They are controlled with viricides or their vectors (insects, mites, nematodes, fungi) are controlled with suitable products.

In principle, preventive measures for disease avoidance, such as the right choice of location and variety and crop rotation, are the first priority. This can delay or reduce pathogen infection and, ideally, prevent it. In addition, the robustness of the crop can be supported with plant strengthening products by increasing its defenses.

If a disease is suspected, for example in infested areas or in weather conditions that promote diseases, early detection, monitoring and identification of the pathogen are prerequisites for targeted control.

To ensure control success, the right product or product mixture must be used at the right time.

In addition, hygiene measures and forward-looking health management are essential for the following years or the following crop in agriculture.

Way of life of phytopathogenic fungi, bacteria and viruses

In fungi, germinating spores and mycelia (fungal tangles) can colonize and feed on both living and dead host cells. In doing so, the fungus either directly invades epidermal cells or uses the infection route via natural plant openings such as stomata (respiration holes), lenticels (cork warts), hydatodes (water-secreting glands), and wounds. Fruiting bodies with spores formed on the plant surface will usually be spread by wind or rain.

Bacteria enter plants through injuries and wounds. This includes bites or stings from vectors. Bacteria multiply and spread passively throughout the plant within the host tissue or with the sap flow.

Viruses are transmitted mechanically by grafting, injury, and vectors (insects, mites, nematodes, fungi). They enter the cell upon contact with the cell wall and multiply there. Spread within the plant occurs with the sap flow towards the growth zones (shoot tip, root), where uptake by vectors occurs.