Plants can fall sick because of many reasons. It is important for gardeners to understand the difference between plant diseases and physiological disorders. The symptoms of both can be quite deceptive and confusing at times. In this blog, we will look at primary symptoms of plant diseases caused due to fungi, bacteria and viruses, signs of plant disorders and their causes.
Symptoms of Fungal diseases:
The prominent and visible external symptoms can help in recognizing fungal diseases.
Rust diseases in many plants are recognized by characteristic rusty spots and pustules, on either surface of leaves.
In mildew diseases, fungi produce a powdery coating of spores and mycelia on the surface of leaves, stems and fruits.
A magnifying glass is useful in observing the spore-bearing structures protruding outside the leaf surface, which will show the presence of Fungi.
The diagnosis of diseases produced by bacteria is not easy in plants. Bacterial infections do not generate any external growth and usually remain confined within plant tissue.
Following are some general symptoms:
Rotting of the mass of tissue in leaves or young shoots.
Sudden wilting of plants foliage.
The sudden collapse of the entire plant.
Burnt spots on leaves, stems and fruits.
Note: Harmful bacteria flourishes in soil if when the soil is not adequately aerated and is over saturated with moisture.
Symptoms of Viral diseases:
The symptoms produced by viruses are somewhat different. Viruses which exist in the sap of plants are very minute and can be only detected by an electron microscope.
Following are some common symptoms of viral diseases in plants:
Curling and distortion of leaves.
Presence of mottles or dry spots on leaves.
Either yellow leaves with green veins or green leaves with yellow veins.
Note: Viruses spread more because of insect vectors and presence of weeds in surroundings.
Physiological disorders:
When the plants show disease-like symptoms without any fungal, bacterial or viral infection, it is generally because of physiological disorders. Often the gardeners can get confused between physiological disorders with diseases due to similar symptoms.
Following are some of the causes of physiological disorders and their symptoms:
Waterlogging: Yellowing of the foliage and ultimate shedding of leaves occurs in herbaceous ornamental plants and shrubs due to waterlogging. If proper drainage is not provided, the affected plants may soon perish. In extreme cases of waterlogging, even large trees are killed.
Drought: Yellowing of foliage and sudden collapse of a plant can occur due to drought. Symptoms can be similar to waterlogging.
Excessive heat: The scorching rays of the sun may cause the edge of leaves to curl, or the edges may turn brown. Sometimes brown spots may also develop all over the surface of the foliage. Tender young leaves suffer more.
Severe cold and frost: The foliage may turn blue, yellow or brown due to severe cold and frost. Frost damage in common in Roses, Dahlias and Salvias. The whole plant may become black by early morning due to overnight frost injury.
Deficiency of plant nutrients also causes disease-like symptoms in plants. Such physiological disorders are sometimes known as deficiency diseases.
