Plant Diseases and Insect PestsPlant Diseases and Insect Pests• DiseaseDisease - any kind of injurious abnormality - any kind of injurious abnormality

– Physiological (environment)Physiological (environment)– Other living organisms (pathogens)Other living organisms (pathogens)

• PathogenPathogen - biological agent that causes the injury - biological agent that causes the injury– InsectsInsects– Bacteria Bacteria – FungiFungi– VirusesViruses– NematodesNematodes– MiscellaneousMiscellaneous

Plant Diseases and Insect PestsPlant Diseases and Insect Pests• ParasiteParasite - an organism that derives nourishment from - an organism that derives nourishment from

another living organism another living organism

• HostHost - an organism that provides nourishment to - an organism that provides nourishment to anotheranother

• Obligate parasiteObligate parasite - organism that can only survive on - organism that can only survive on the living hostthe living host

• Host rangeHost range - list of several different plants that some - list of several different plants that some parasites can feed off ofparasites can feed off of

Plant Diseases and Insect PestsPlant Diseases and Insect Pests

• BacteriaBacteria - one-celled organisms that - one-celled organisms that enter through wounds and cause rotenter through wounds and cause rot

• FungiFungi - multi-celled organisms that either - multi-celled organisms that either are saprophytes or parasites. Ex: molds, are saprophytes or parasites. Ex: molds, mildew. Cause decay of plantsmildew. Cause decay of plants

Bacterial rot/wiltBacterial rot/wilt

Fireblight on an appleFireblight on an apple

Bacterial disease control?Bacterial disease control?

• Start with clean pots & potting media & toolsStart with clean pots & potting media & tools

• Start with clean seed or healthy transplantsStart with clean seed or healthy transplants

• Use drip irrigation or water in the morning so the Use drip irrigation or water in the morning so the extra water on the surface of the leaves evaporates extra water on the surface of the leaves evaporates by eveningby evening

• Antibiotics now exist for injecting into trees but Antibiotics now exist for injecting into trees but treatment is costly and the effects temporary. treatment is costly and the effects temporary. There are no antibiotic spray treatments.There are no antibiotic spray treatments.

Fungal rotsFungal rots

Fungus on foliageFungus on foliage

Fungal disease control?Fungal disease control?

• Start with clean pots & potting media & toolsStart with clean pots & potting media & tools

• Start with clean seed or healthy transplantsStart with clean seed or healthy transplants

• Use drip irrigation or water in the morning so the Use drip irrigation or water in the morning so the extra water on the surface of the leaves evaporates extra water on the surface of the leaves evaporates by eveningby evening

• Fungicides do exist. They can be used as a liquid Fungicides do exist. They can be used as a liquid drench, spray or powder.drench, spray or powder.

Captan & Thiram = Captan & Thiram = synthetic fungicidessynthetic fungicides

Plant Diseases and Insect PestsPlant Diseases and Insect Pests

• VirusesViruses - infectious particles made-up of - infectious particles made-up of nucleic acids (typically RNA in plants) with a nucleic acids (typically RNA in plants) with a protein coat. In the plant cell, the protein coat protein coat. In the plant cell, the protein coat comes off and the RNA uses the plant cell to comes off and the RNA uses the plant cell to reproduce itself. These are obligate parasites.reproduce itself. These are obligate parasites.

VirusVirus

Tobacco Mosaic VirusTobacco Mosaic Virus

No control methods!No control methods!

• NematodesNematodes - unsegmented worms that - unsegmented worms that feed on roots and create wounds for feed on roots and create wounds for bacteria and fungi to enterbacteria and fungi to enter

Plant Diseases and Insect PestsPlant Diseases and Insect Pests

Nematode Nematode damage damage

on tomatoon tomato

Nematode damage on tomatoNematode damage on tomato

Nematode damage on carrotNematode damage on carrot

Foliar nematodesFoliar nematodesHostaHosta ZinniaZinnia

How Plants are DamagedHow Plants are Damaged

• Damage by:Damage by:– Direct feedingDirect feeding– Secretion of toxic substancesSecretion of toxic substances– Secondary organism enters the woundSecondary organism enters the wound

• SymptomSymptom - plant’s response to attack (wilt)- plant’s response to attack (wilt)

• SignSign - structures produced by the attacking - structures produced by the attacking organism (webs, tunnels, etc.)organism (webs, tunnels, etc.)

Symptom = wiltSymptom = wilt

Webbing = signWebbing = sign

Spread of Insects and DiseaseSpread of Insects and Disease

• Diseases and insects are spread to plants by:Diseases and insects are spread to plants by:– WaterWater– WindWind– InsectsInsects– Animals (including people) Ex: TMVAnimals (including people) Ex: TMV– MachineryMachinery

• Plants are more susceptible to disease and Plants are more susceptible to disease and insect attack when they are stressed (water insect attack when they are stressed (water or temperature)or temperature)