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TYPES OF PESTS - DISEASES CAUSING PESTS AND WEEDS
DISEASE-CAUSING PESTS

pathogens - microorganisms that invade, infect and cause damage to another living organism.
 
Type Microorganism
Appearance/Symptoms on Plant
1) fungi
long, multicellular filamentous microorganisms composed of membrane-bounded cells surrounded by  cell walls
  • moldy or powdery appearance on leaf
  • causes necrotic spots
2) bacteria
usually rod shaped, single-celled (may form filaments) microorganisms composed of a membrane-bounded cell surrounded by a  cell wall.
  • causes soft, mushy, odorous regions on leaves or stems, "soft rot"
  • causes circular, ringed lesions
3) virus
rod-shaped, spherical or crystalline-shaped microorganisms  composed of strands of nucleic acids surrounded by a protein coat.
  • causes yellow mosaic or mottling of leaves
4) mycoplasma  and spiroplasma
pleomorphic (means takes on shape of the organism it is in) microorganisms with membrane-bounded cells, but without cell  walls.
5) rickettsia-like organisms
bacteria-like organisms that can only live inside living cells

 WEEDS - any plant out of place.

     Cause Damage by: 
    1) competition

     2) allelopathy 

     3) expense

     4) disease and insect hosts

     5) contaminate foods

     6) poisonous

     7) aesthetically undesirable

     8) parasite, ex. dodder, mistletoe