Pests and Diseases ,Their impact on Agriculture

Group Members

D.M.U.D.DISSANAYAKE AG07/08/25

P.V.EKANAYAKE AG07/08/27

W.K.A.D.EKANAYAKE AG07/08/28

Plants•Plants are primary producers of food for human as well as beneficial of human welfare.•Apart form their role as suppliers of foods, sources of medicines etc.•Survival of plant is key of life on earth.•Shortage of food is probably the most important challenges in the present day civilization.•Shortages of foods can be attributed to several causes, one is losses caused by enemies of plants.

Statistics

•On a global basis about 33%of crops is lost annually due to diseases, insects pests and weeds.•In cereal ,the annual loss is estimated to be about 18% in developed countries and 46%in developing countries.•Percentage of all produce lost to diseases, insects, and weeds are in 25%Europe,29%North and Central America,30%Russia and china,42-43% Africa and Asia.•Of the 35% annual crop loss,12% caused by fungi, bacteria, and viruses,11%due to diseases caused by nematodes,7%due to insects and 3%due to weeds.

Plant disease

•Plant is a normal part of the nature and is one of many ecological factors that help kept the hundreds of thousands of living plants and animals in balance with another.•When the plant is suffering,i.e.,not developing and functioning in the manner it is expected, we can called diseased.

Causes of plant disease

•A pathogen is always associated with a diseases. the word pathogen can be broadly defined as any agent or factor that incites “pathos "or diseases in an organism.•Thus n strict sense the pathogen do not necessarily belong to living or animate groups.•They may be non living or in between the living and non living.•The plant pathogens are thus grouped under following categories. Causes for diseases

Abiotic factors Biotic factors Mesobiotic factors

•Abiotic factors- These indicate mainly the deficiencies or excess of nutrients such as light,moisture,areation,abnormalities in soil conditions ,atmospheric impurities.

Ex-Mango fruit rot, Black heart of potato.

•Biotic factors- This category includes diseases caused by animate or living or cellular organisms.

•Mesobiotic factors – Theses disease incitants which are neither living nor non living .They are considered to be on threshed of life.

Viroids- Spindle tuber of potato, Tomato bunchy top

Viruses- Leaf roll of potato, Leaf curl of tomato and chilly

pests

•Plants provide food for many forms of life. Human beings and other grazing animals depend on plants for food. •It is important to note that large numbers of other much smaller creatures such as insects and their larvae also feed on plants. •Living being which, feed on plants and cause damage to the plants are called pests. •Plant pests vary from place to place. •The study of plant pests are useful and especially to farmers

Common pests in the World

•Aphids They are very small with light colored bodies. They leave a sticky residue on the leaves. Remove damaged leaves.•Caterpillar Most kinds of caterpillar are considered plant pests and will eat the leaves.•Colorado Potato Beetle Inch long striped beetles and their larvae will eat everything on a plant.•European Corn Borers Small, 1 inch long caterpillars who bore into plant stems and eat them from the inside out.

•Leaf Hoppers Small, 1/8 inch long, wedge shaped insects that suck the sap through the plant leaves. •Mealy bugs Small bugs create white, powdery masses on leaf stem joints. Scrape off and spray with insecticide. •Root Maggots Fly larvae that hatch at the base of the plants and eat the roots.•Thrips Very small and slender bugs leaving dark blobs on the leaves.•Whiteflies Tiny, white flying bugs .

Pest and Disease impact on Agriculture

Resulting the food shortages

oThe late blight of potato, a disease caused by the fungus ,Phytophthora infestans,is a famous example of what a plant disease can do to change the course of history.•In 1845 this diseases destroyed the potato crop of Ireland where potato constituted the staple diet of the majority in rural areas.•The disease had started in Ireland ,England, and parts of the continental Europe as early as 1830 and was causing some damage every year, resulting in food shortage.•When late blight epidemic destroyed of the potato crop in 1845 there was famine in Ireland.

•The demographic data are highly variable but it was reported that in 1840the population of Ireland was 8 million reduced to 4 million after the famine.•Hundreds of thousands perished from hunger and diseases.•There was large migration of population to other countries including the North American continent where 6 million are reported to have migrated between 1847and 1854.

Change the food habit of the population

oWheat rust is a another disease that has appeared in epidemic from time to time in many countries.•This disease has forced the farmers in the many part of the world to change their cropping pattern .•Wheat has been replaced by corn or rye because it was regularly destroyed by rust.•This caused change in the food habit of the population in affected areas.

Loss of economic returns of farmersoIn India ,wheat rust has been considered to cause a loss over Rs.400 million annually.•In the years of epidemics there have been losses amounting to Rs.500 million or more.•Although introduction of dwarf varieties has reduced the loss to a great extent even the farmer lose 8-10% of the expected yield due to rusts.

oThe loose smut of the wheat is another disease is estimated to cause an average loss of 3%(about Rs.500 million)every year.

•This disease of wheat and barley prevalent in most part of the India ,causes a loss of Rs.30 million in barley and 30 million in wheat in every year.

Completely destroyed or vanished whole cultivation

o In the middle of the nineteenth centaury coffee and tea equally consumed in England because these were available in plenty from such occupied countries as India, Sri Lanka and Malaya.•Sri Lanka used to produced maximum coffee in the world.•In 1867 coffee rust attacked the plantation in Sri Lanka and by 1893 the export of coffee from Sri Lanka had declined by93%.

•The economic crisis forced the planters to cut down coffee plant and take to tea planting.•Export of tea revived the economy to some extent and at the same consumption of tea increased in England.•When coffee rust was spreading in Sri Lanka the science of plant pathology was just developing and control measures for the disease were known.

Reduction of yield

oAn estimated 100,000 coconut trees in southern Sri Lanka have been affected by a disease that is being termed “Weligama coconut leaf wilt disease”. •The disease which was diagnosed in 2006 is transmitted mainly by insect vectors that absorb juice from an infected tree and then move on to another, thereby infecting many trees in the process.

•Leaf Rot Disease” and “Weligama Leaf Wilt Disease” have affected large number of coconut trees in the Southern Province. •These diseases are found in Matara District, Galle District •(Habaraduwa and Galle AGA Divisions) and Hambantota District (Walasmulla, Beliatta and Tangalle AGA Divisions). •As the name implies, it involves the rotting of the leaves along with crown reduction, yield reduction and death of the palm in 3-5 years. •“Weligama Leaf Wilt Disease is caused by a group of organisms called phytoplasma, which lives in the phloem tissue.

•The “Weligama Coconut Leaf Wilt Disease” (WCLWD) is a “silent killer”. It has been attacking coconut trees in several areas in the South for the last four years. •According to the recent sample survey, there are about 360,000 trees affected in Galle, Matara and Hambantota districts. It has caused 45% coconut yield reduction in all three districts.”

oKernel bunt of wheat, root knot of tomato, eggplant and cucurbits, apple scab, mango malformation, bunchy top of banana are responsible for huge losses.

oRice blast is one of the most destructive diseases of rice.•In India, more than 266,000 tons of rice were lost, which was about 0.8% of their total yield.• In Japan, the disease was reported to occur in about about 865,000 hectares of rice fields.• In the Philippines, yield losses ranging from 50 - 85% were reported before the introduction of resistant varieties.•In rice blast infected panicle turns white, causing panicle blast, and dies before being filled with grain. The infected node rots causing all above parts to die.

Reduction of nutritional value of crops and reduced the consumer preference

oPapaya ring spot, caused by papaya ring spot virus, is the most important disease of the crop in Florida, severely limiting the potential for commercial production. •Earliest symptoms appear as yellowing and vein-clearing of younger leaves. A prominent yellow mottling of the leaves.

•These consist of circles and C-shaped markings that are darker green than the background fruit color .Later, these markings may become gray and crusty in texture.•Infected plants exhibit growth reduction. There is reduced fruit set, and quality, especially flavor, is adversely affected.oAnthracnose is a post-harvest rot of bananas that affects the fruit quality and marketability.•Anthracnose, caused by the fungus Colletotrichum musae, The fungus that causes anthracnose also causes crown rot, another rot disease of bananas.

•Symptoms consist of brown to black blemishes on the fruit, fruit rot, lesions on the fruit and premature ripening.• Orange or salmon colored rings may occur on severely infected bananas.•That reduce the consumer preference and loss huge number of nutrients.

Reduce esthetic value of the cropoMango scab-due to microbial insfection.can see ulcer like lesions in epidermal cells. Therefore reduce the esthetic value of fruit.

oThe carrot tubers are exposed in to the excess sunlight, form chlorophyll and turn in to green color.-reduce the market value of carrot tubers.

oBirds eye of Grapes –the water soaked sunken areas appear in the peel of grapes, These areas appear as birds eye.•The spots in the berries enlarge in size and finally leading to shriveling and dropping up of the berries•In sever infection ,several necrotic lesions are formed on the each berries, the pulp of the berry become rot.

Act as vectors and transmit viral diseases

oAphids in bananaAphids suck young leaves whish become curled and crinkled, and even defoliate, especially at seedling stage. Some aphids also transmit the virus diseases.

Brown plant hoppers in paddy also transmit ragged stunt and grassy stunt viruses.

oGreen leafhopper (GLH) Nephotettix virescens in paddy-They can cause indirect damage to the crop because of the virus diseases that they transmit. Green leafhoppers are important pests. They are vectors of viruses such as tango, yellow dwarf, yellow-orange leaf, transitory yellowing, and dwarf.

Reduce the quality of the yield

oToday, potato is the fourth most important crop in developing countries

Researchers estimate that developing country farmers spend $700 million annually to control The main biotic constraints

Production for 2004World: 330,732,457 metric tonsArea Harvested in 2004World: 18,999,125 hectares

quality and yield of potato deteriorated by pest and diseases.

Eg- some investigations in potatoes showed the presence of main destructive pests, such as potatoes tuber picker , black cutworm, Gryllotalpa spp., leaf roll, and pear trips.

oIn papaya mealy bug feeds on the sap of plants by inserting its stylets into the epidermis of the leaf, as well as into the fruit and stem. •In doing so, it injects a toxic substance into the leaves. The result is chlorosis, plant stunting, leaf deformation, early leaf and fruit drop, a heavy buildup of honeydew, and death. •Heavy infestations are capable of rendering fruit inedible due to the buildup of thick white wax.

oCorn smut is a disease of maize caused by the pathogenic plant fungus Ustilago maydis.•It can infect any part of the plant it usually enters the ovaries and replaces the normal kernels of the cobs with large distorted tumors analogous to mushrooms.. These tumors, or "galls", are made up of much-enlarged cells of the infected plant, fungal threads, and blue-black spores.• The spores give the cob a burned, scorched appearance.

Finally.•Plants are extremely important in the lives of people throughout the world. People depend upon plants to satisfy such basic human needs as food, clothing, shelter, and health care. These needs are growing rapidly because of a growing world population, increasing incomes, and urbanization .•There fore we have to pay our attention towards to the pests and diseases of the cultivated crops and take suitable actions to control them and finally make the world phosphorus with foods.

References

http://theseedsite.co.uk/pests.html

http://en.wikipedia.org/wiki/Plant_pathology

http://www.dgsgardening.btinternet.co.uk/disease.htm

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