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Crop Protection: Chemical Control by Pesticides and Its Pros and Cons

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Crop Protection: Chemical Control by Pesticides and Its Pros and Cons Crop protection: Chemical control by Pesticides and its Pros and cons, Biological control: Management of plant diseases caused by fungi, Bacteria, virus, nematodes and insects; Microbial herbicides; Bacterial biopesticides; Production of biopesticides; Fungal biopesticides; Entomo-pathogenic fungi, benefits of biological control, Integrated pest management, Maintaining virus free plants. Mitesh Shrestha Principles of Control • Exclusion – Prevent pathogens from being introduced in the first place • Eradication – If pathogens are established measures are taken to stop the spread and reduce populations • Protection – Isolate the host from the pathogen • Resistance – Plant is equipped with disease resistance A Pest Defined • Technically, any organism (bacteria, fungi, plant, animal) that has a negative effect on human health or economics (food). • Realistically, any organism we don’t want around (factors in convenience and esthetics). Preventing Pest Attack • Certain environmental conditions predispose plants to diseases • Select and use adapted cultivars • Use pest-resistant cultivars • Plant at the best time Preventing Pest Attack • Provide adequate nutrition • Observe good sanitation • Remove weeds • Use quality seeds or seedlings • Prepare the soil properly Controlling Insect Pests • Chemical control • Biological control • Cultural control • Regulatory or legislative control • Mechanical control • Integrated Pest Managment Fungicides • Protective – Protect plant surface • Systemic – Penetrate the plant tissue • Organic – More selective, pose less environmental danger • Inorganic – Sulfur, copper, mercury Other Pesticides • Nematicides – Nematodes • Rodenticides – Rodents • Molluscides – Snails and slugs • Miticides – Mites • Aviacides – Birds Decision making process of pest control • Detection • Identification • Biology and habits • Economic importance • Choice of method • Application • Evaluation • Record keeping Pesticide Toxicity • Toxicity – The relative capacity of a substance to be poisonous to a living organism. • Oral • Inhalation • Dermal • Lethal Dose (LD50) – The milligrams of toxicant per kilogram body weight of an organism that is capable of killing 50% of the organisms under the test conditions. Methods of pesticide application • Foliar application • Soil treatment • Seed treatment • Control of postharvest pests Chemical Technology Problems • Resurgences: after “eliminating” a pest, its population rebounds in even higher numbers than previous levels. Why? • Secondary outbreaks: outbreaks of species’ populations that were not previously at pest levels. Why? Think about mechanisms of environmental resistance on any one population. Some Examples of Insect Food Chains When Will It End? Human Health Effects • Acute: high dose, short-term response, rapid onset (headache, nausea, vomiting, respiratory failure, death). Agricultural workers suffer acute poisoning during pesticide application. • Cronic: low-dose, long-term exposure, outcome takes many years before noticed (cancer, dermatitis, neurological disorder, birth defects, sterility, endocrine system disruption, immune system depression). Neighborhoods downwind of agricultural use; farm families; the innocent. Environmental Effects • Bioconcentration: – Movement against a concentration gradient; typically fat soluble. • Biomagnification: – Movement through the food chain to higher trophic levels; typically persistant. • Bioaccumulation: – Combined effect of both; chemicals are typically fat soluble and persistant. The DDT Case Study • 1938; dichloro-diphenyltrichloroethane (DDT) • Extremely toxic to insects, but seemed nontoxic to humans and other mammals. • Cheap. • Broad-spectrum and persistent • Effective for disease prevention (typhus fever, malaria) • Expanded agricultural production • Paul Muller awarded Nobel prize in 1948 Bioaccumulation & Biomagnification What is biological control? • First coined by Harry Smith in relation to the biological control of insects – Suppression of insect populations by native or introduced enemies • Generic terms – A population-leveling process in which the population of one species lowers the number of another Biological Control • Use of living organisms to reduce disease due to competition or antagonism – i.e.. ladybugs to control aphids • The aim is to reduce dependence on chemicals • Today emphasis on microorganisms – Bacillus thuringiensis for insect control – Several Pseudomonas species for control of bacterial and fungal pathogens – Numerous fungi for insects, nematodes, fungal pathogens Why use biological control? WHEN : • Biological control agents are – Expensive – Labor intensive – Host specific WHILE : • Chemical pesticides are: – cost-effective – easy to apply – Broad spectrum Why use biological control? WILL: • Chemical pesticides – Implicated in ecological, environmental, and human health problems – Require yearly treatments – Broad spectrum • Toxic to both beneficial and pathogenic species BUT: • Biological control agents – Non-toxic to human – Not a water contaminant concern – Once colonized may last for years – Host specific • Only effect one or few species Mechanisms of biological control of plant pathogens • Antibiosis – inhibition of one organism by another as a result of diffusion of an antibiotic – Antibiotic production common in soil-dwelling bacteria and fungi – Example: zwittermicin A production by B. cereus against Phytophthora root rot in alfalfa Mechanisms of biological control of plant pathogens • Nutrient competition – competition between microorganisms for carbon, nitrogen, O2, iron, and other nutrients – Most common way organisms limit growth of others – Example • P. fluorescens, VITCUS, prevents bacterial blotch by competing with P. tolaasii Mechanisms of biological control of plant pathogens • Destructive mycoparasitism – the parasitism of one fungus by another – Direct contact – Cell wall degrading enzymes – Some produce antibiotics – Example • Trichoderma harzianum, BioTrek, used as seed treatment against pathogenic fungus Requirements of successful biocontrol 1. Highly effective biocontrol strain must be obtained or produced a. Be able to compete and persist b. Be able to colonize and proliferate c. Be non-pathogenic to host plant and environment Requirements of successful biocontrol 2. Inexpensive production and formulation of agent must be developed a. Production must result in biomass with excellent shelf live b. To be successful as agricultural agent must be i. Inexpensive ii. Able to produce in large quantities iii. Maintain viability Requirements of successful biocontrol 3. Delivery and application must permit full expression of the agent a. Must ensure agents will grow and achieve their purpose Coiling of Trichoderma around a pathogen. (Plant Biocontrol by Trichoderma spp. Ilan Chet, Ada Viterbo and Yariv Brotman) Biological Control of Pests • Pre-predator relationships • Antagonism • Repellents • Alternative hosts • Biocontrol • Microbial sprays Bacillus thuringiensis • Common soil bacterium well known for its ability to produce crystalline proteins with insecticidal properties • Since 1960s Bt available as a safe naturally occurring biopesticide – Use as a dried inoculum containing endospores and crystals of insecticidal proteins – used as sprays or dusts for a wide variety of insects - especially Lepidopteran Bt Toxins • Toxins activated by enzymes in insect gut • Kill insects by binding to membranes in digestive system and creating pores in membrane~contents leak into body cavity • Harmless to humans, natural enemies of arthropods, and non-target organisms Bacillus thuringiensis • B.t. subspecies kurstaki is widely used in caterpillar control in agriculture and forestry • B.t. subspecies israelensis is active against mosquitoes and black flies • B.t. subspecies tenebrionis is active again beetle larvae Bt Uses • Spray Applications – Bt toxins degrade within a few days – Endospores can survive for several years after spray applications • Genetic Engineering with Bt genes – Transfer into crop plants – Transfer other bacteria Pseudomonas species • Pseudomonas fluorescens for control of fire blight (also may control apple blue mold) • Fire blight – bacterial disease of apples and pears caused by Erwinia amylovora • Pseudomonas out competes Erwinia • Reduces use of streptomycin which has been helpful since many Erwinia strains resistant Natural Pest Control • Cultural control • Control by natural enemies • Genetic control • Natural chemical control Cultural Control of Pests • Crop rotation – Related species and monoculture • Sanitation • Resistant cultivars • Host eradication • Mulching Cultural Control Get rid of the alternative host! Control by Natural Enemies Genetic Control • Plants or animals are bred to be resistant to the attack of pests. – Chemical barriers. – Physical barriers. • Introduction of genes into crops from other species: transgenic crops (Bt) • Sterile males are released into pest population. Natural Chemical Control • Manipulation of pests’ hormones or pheromones to disrupt the life cycle. • Japanese beetle trap. Regulatory or Legislative Control • Plant quarantines – Emerald Ash Borer – Gypsy Moth – Potatoes Integrated Pest Management Methods • People who practice IPM (integrated pest management) understand that eradicating insect pests and diseases of plants is usually unrealistic. • IPM primarily consists of methods used to prevent plant problems from occurring in the first place. Pest Management Methods • To practice IPM in the landscape, choose plants
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