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| CROP DISEASES & MINERAL DEFICIENCIES
1 To discuss basic principles of crop diseases 2. To describe and view symptoms of diseased crops 3. To discuss the role of essential nutrients in crop production 4. To describe and view plant nutrient deficiency symptoms. Introduction According to Janick et al. (1981), an ancient Egyptian scribe once wrote: Worms have destroyed half the wheat, and the hippopotami have eaten the rest; there are swarms of rats in the fields, the grasshoppers alight there, the cattle devour, the little birds pilfer; and if the farmer loses sight for an instant of what remains on the ground, it is carried off by robbers... This brief quote highlights the challenge that farmers have faced in their battle against crop pests since organized agriculture began. A quick examination of current statistics shows that despite modern technology, plant pests such as diseases continue to have a major impact on food production. The FAO (Food and Agriculture Organization of the United Nations) estimated in the early 1980's that about 35% of the world's wheat crop was lost to diseases and insects. They estimated the loss in potatoes at 40%, in apples 30%, and in cotton 60%. In the U.S. the damage to crops from diseases and insects may be as high as $12 billion a year. A number of disease and insect pests in the U.S. have been imported into the country by early colonists or recent travelers. Bringing in contaminated seed or contaminated plant material has often been the culprit. What major pest of wheat was brought to the U.S. by German soldiers hired by the British during the Revolutionary War in straw bedding? A plant disease may be defined as the harmful alteration of the normal development of the plant. (Hartmann et al., 1981). This definition includes not only biological pathogens (living agents that cause diseases) but also mineral deficiencies. What living pathogens cause crop diseases ? What three conditions are required for the development of a crop disease: 1. 2. 3. Controlling Plant Diseases Methods for controlling plant diseases generally fall into three categories: 1. 2. 3. Biological control includes the use of resistant species and cultivars of crops. Nature tends to select resistant crops and varieties naturally, since susceptible plants are gradually eliminated. However crop geneticists and crop breeders also work constantly to select and breed crops that are resistant to diseases. What would be one good example of how plant breeders have contributed to lower pest losses in crops through crop breeding?
Crop rotation is the classic example of cultural control of diseases. Rotating to a crop that is not a host for a particular disease causing organism is an effective way of controlling diseases in crops. Another example of cultural control would be government inspection and quarantine of certain plants or their seed. Mangoes, and guavas grown in Hawaii have been prohibited from entry to the U.S. Mainland because they may carry the Mediterranean fruit fly. Diseased plants eventually show visible symptoms that vary in appearance and location, as illustrated by the diagram below. With your instructors help, fill in the appropriate information in the blanks associated with the diagram. Describe 7 major crop disease symptoms: 1. 2. 3. 4. 5. 6. 7. What are some important plant diseases caused by bacteria ?
Fungal Diseases Most plant diseases are caused by fungi. The famous Irish potato blight of the 1840's was caused by the fungus Phytophthora infestans, and resulted in the death of more than 1 million people by starvation. In more recent years the wheat stem rust, caused by the fungus Puccinia graminis tritici has occasionally caused serious damage to wheat crops in the U.S. What are some important crop diseases caused by fungi?
VIRAL DISEASES OF CROPS Viruses are very small particles that may or may not be defined as living entities. They are composed of an outer sheath of protein and an inner core that is often ribonucleic acid (RNA). Viruses require a living host organism to complete their life cycle, in other words they are parasitic. They must have a host or insect carrier to multiply and spread. What are some crop diseases caused by viruses? Mycoplasmas are microscopic living organisms that contain DNA and RNA. They produce filaments like fungi that can break up into small particles that can in turn form more branching filaments. Mycoplasmas or mycoplasma like organisms have been known to infect animals for some time, but in recent decades a number of plant diseases are attributed to mycoplasmas. Examples of diseases caused by mycoplasmas or mycoplasma like organisms include: How are mycoplasmas transmitted?
The most obvious method for controlling the spread of these diseases is a program to eliminate insect carriers (vectors). Another means of control is to use certain antibiotics. For example, pear trees may be injected with solutions of the antibiotic tetracycline to control pear decline disease. MANAGEMENT TO MINIMIZE DISEASE PROBLEMS Describe management practices by which a crop producer can minimize disease problems. Fill in the table below to describe chemical and non-chemical means of controlling some important crop diseases.
CROP MINERAL DEFICIENCY In addition to monitoring crops for diseases, weeds, and insect pests, a crop producer must be aware of any mineral deficiencies present in a growing crop. Mineral deficiencies may result in lowered yield, quality, or disease resistance. In today's laboratory we will discuss important mineral deficiencies in crops and view some figures illustrating some of these symptoms. In the table below, list the abbreviations and full names of essential elements required by crop plants: Instructions With the help of your instructor and with slides/overheads/figures provided, fill in the information requested in the following tables.
Save the Earth: Feed the World 1. Fully 1/4 of american fruits and vegetables are grown where?
2. Pesticide sprays affect more than just insects. What else is potentially affected? A. B. C. 3. The government estimates that americans get cancer from pesticide residues each year. What percentage is this of our population, assuming 250,000,000? 4. According to the film, the key to the success of farms in the 1830's was: A. B. 5. What are the main two benefits of crop rotation that were stated ? A. B. 6. What was the green revolution ? 7. What were the short and long term results of the green revolution that were given ?
8. What happened during the Green Revolution that resulted in an increased problem with the brown plant hopper. 9. What was the main attack against the hopper ? 10. Which continent has the worst record in soil conservation ? 11. What is the threefold problem in Australia that caused such a problem with soil erosion ? A. B. C. 12. What were three remedies given to help alleviate erosion? 1. 2. 3. 13. It was stated that in meeting the food needs of the world, we are fighting on two fronts. What were they? A. B. 14. What is meant by low input agriculture?
15. What was an antidote to controlling aphids on the organic farm on artichokes? 1. 2. 16. What were two crops mentioned that were said to be drought-tolerant? 1. 2. 17. What lessons would you learn from this experiences presented in this video that would impact how you would produce crops? |
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