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Biological control of plant diseases
One parasitoid attack only on one host, and remain alive as a free-living adult in the host. The size of the parasitoids is the same as the host or may be smaller than the host.
The female parasitoid lays eggs inside or on the insect host. The egg hatched and legless larva affects the host on the surface or internally. A large number of parasitoids feed on pollen and act as pollinators.
Pathogens are disease-causing organisms (bacteria, fungi, viruses, protozoa, and nematodes) in insect pests that cause, death of the host or make weak the future generation.
The disease-causing organism (insects) are unable to feed properly, cannot grow properly means remain stunted. They lose the color of the body and get paralyzed. The dead insects are present/observed in the form of hanging on the plants or fungal growth also observed on the body of dried insect could be easily located in the field.
Caterpillar, Pseudoplusia includens, killed by the entomopathogenic fungus, Nomuraea rileyi, white-disease in soya bean crop.
These are free-living organisms and their size is large as compared to their prey, to complete their life cycle predators require prey. Various smallest predators secrete a powerful poison, that is used to catch or kill the prey in the form of groups.
Green lacewings (it is a very important and common predator of crop pests) female predators put down small pale green, oval-shaped eggs during the end stage of large silken stalks, that is ultimate turns to grey. The larvae have well-developed legs and pincer-like jaws. Through the help of these jaws, they observe the body fluids from the prey.
4- Antagonists of plant disease
The microorganism used in biological suppression of plant diseases which grow in association with plant diseases are termed as antagonists. The antagonist’s M/O adversely affects the disease-causing organism by the following:
It is an interaction between two organisms or species in which both are harmful to each other on the base of their resources such as food, water, territory.
It is a biological interaction between two organisms that is injurious to one of them.
Antibiosis provided by marigold roots that release/secrete terthienyls, which is a chemical that are toxic to the many nematodes and fungi species.
The term hyper parasitism is defined as an organism that is parasitic on or in another parasite which is harmful.
As the name indicates myco means fungus so mycoparasitism is defined as the Parasitism of a fungus to another fungus (mycoparasitic) Trichoderma harzianum used as seed treatment against pathogenic fungus (Sclerotium rolfsii) on chickpea and sugar beet.
Image Source: Tecnologia Horticola
Chemical control of plant diseases
The main objective of chemical control is to prevent the crops from pest’s attack and disease at an acceptable level.
The chemical that are to protect the crops from attacks and diseases
It can be used on fruits, foliage, flowers, seeds, and soil.
1- Antibiotics as a chemical agent (bactericides)
Antibiotics are chemically produced by the microorganism, which kills or injures living organisms.
Streptomycin is an antibiotic that is used against some fruit pathogens, such as cankers and blights.
It is a specific type of pesticide that is used to prevent fungal disease by killing or stop the growth/development of the disease-causing fungus.
Cabrio EG, used for cucurbit, fruiting, bulb and root vegetables.
Dithane, it is a protectant fungicide
Nematicides are expensive so their use is largely confined to horticultural crops which have the potential to give high economic returns per unit area
Example: Nema-Q, DiTera DF