Plant pests

1. Plant pests • Noninfectious plant diseases • Plant problems caused by unfavorable environmental conditions • Plant diseases • Ozone (O3) produced by photochemical reaction involving pollutants; causes stipple on leaves • Excessive water causes wilting, stunted growth, chlorosis, abscission of lower leaves

2. Plant pests • Infectious plant diseases • Infections caused by pathogens such as fungi, bacteria or viruses that live within the plant • Plant diseases • Pathogens attack only certain species of plants, often specific organs or tissues such as leaves and fruit • Main types of disease-causing pathogens • fungi • bacteria • virus • Mycoplasma-like organisms

3. Plant pests • Fungi • Cause many diseases such as clubroot of crucifers, potato and apple scab, powdery mildews, corn smut, rusts • Plant diseases

4. Plant pests • Fungi • Other common fungi infections • Plant diseases • Dampingoff: stem rot in seedlings near the soil line of wet soil • fungi eliminated with heat treatment of soil • spread by disinfecting with bleach

5. Plant pests • Fungi • Other common fungi infections • Plant diseases • Dutch Elm Disease: fungus that infests vascular tissue • 1st discovered in Holland in 1921; brought to US in 1930s and has killed most American Elms • Causes wilting, vascular clogging and eventually death (tree blocks own vascular tissue to try to contain disease) • Tip of branches starts to yellow (flagging) then tree should be removed to prevent spread of disease • Disease spread by bark beetles and root graphs • Disease-resistant cultivars of American Elms now being planted

6. Plant pests • Fungi • Fungal pathogens have altered tree species in northeastern forests such as Pine Lake • Plant diseases • American Chestnut Blight killed most dominant tree species in early 1900s • American Beech at Pine Lake infected with Beech Bark

7. Plant pests • Bacteria • Bacterial diseases caused by bacilli (rod-shaped) bacteria • Plant diseases • Leaf spots, cankers, galls, soft rots, blights

8. Plant pests • Bacteria • Bacterial diseases often more difficult to control than fungi • Plant diseases • Bacterial infection prevented by: • Sanitation of equipment • Careful watering to prevent water drops on leaves • Prevent wounding plants (entry for bacteria) • Some chemical can help reduce bacterial infection such as copper compounds and expensive antibiotics • Citrus canker was serious problem in Florida

9. Plant pests • Mycoplasma-like organisms • Organisms intermediate between bacteria and viruses • Plant diseases • All are parasitic on other organisms • Spread by leaf hoppers and other insects • Cause many specific diseases in certain plants (e.g. peach x-disease) • Controlled with antibiotics injected into plant stems or by controlling insect vectors

10. Plant pests • Viruses • Tiny organisms composed of DNA (or RNA) and protein coat; viruses without protein coat called viroids • Plant diseases • Most viruses named after the major host and symptom they cause (e.g. tobacco mosaic virus) • Often cause symptoms on leaves: chlorotic flecks, leaf rolling, necrotic spots, ring spots • No effective control other than using good sanitation (viruses easily spread by asexual propagation) • Insects act as vectors for viruses, particularly the sucking insects such as aphids and leafhoppers

11. Plant pests • Viruses • Use of uninfected apical meristems in tissue culture is one way to rid plant strain of virus • Plant diseases • Common viral plant diseases: • Tobacco mosaic virus • Common in tobacco and tomatoes (and > 100 other dicots including marigolds) • Damages leaves (yellowish blotches), flowers and fruits; stunts growth and reduces yields

12. Plant pests • Viruses • Common viral plant diseases: • Plant diseases • Apple mosaic virus • Similar to TMV; causes reduced yield (up to 50%) of some cultivars of apples

13. Plant pests • Viruses • Common viral plant diseases: • Plant diseases • Alternaria • Causes dark rings on leaves with necrotic centers