THE CONTROL OF PESTS AND WEEDS

1. THE CONTROL OF PESTS AND WEEDS

2. CHEMICAL INSECTICIDES 1. Traditional method 2. DDT – after World War II. Highly effective but had serious side effects: i. residues persistent in environment ii. Toxic to other species iii. Concentrate in higher trophic levels iv. Eggshell thinning in raptors – top of food chain v. Rachel Carson “Silent Spring” vi. pests evolve resistance – promotes more use e.g. Red scale Insect on oranges California vii. Can release other herbivores as pests – in Cotton fields Pink bol worm released after Cotton bol worm sprayed with DDT

4. BIOLOGICAL CONTROL Definition: The use of biological agents to depress but not eradicate pests and weeds

5. BIOLOGICAL CONTROL Positive factors: 1. Pests can be controlled by introducing predators and parasites from their home countries 2. Such pests are often in low density at home suggesting predator control 3. Permanent if it works 4. Avoids insecticide pollution 5. Agents get into inaccessible places

6. BIOLOGICAL CONTROL Negative factors: 1. Sometimes unwanted results – e.g cane toad 2. Leaves more exotics in the environment 3. Successes are few and only partial: Of herbivorous insects introduced to control weeds 39% have no effect 41% of introduced agents have only partial effect 20 % major effect

7. European rabbits – exotic to Australia

8. Rabbits at waterhole, Australia 1950s

9. One night’s rabbit catch 6228 in 1906 Australia

10. EXAMPLES OF SUCCESSFUL BIOLOGICAL CONTROL Mammals: The rabbit in Australia 1. First brought in 1788 with first emigrants, 1859 first “wild type” in a park 2. Bush fire burns fences, rabbits escape – 1863 3. Rabbits start to spread. Employ rabbit trappers to prevent spread 4. 187-1900 – rabbits spread west and north helper by trappers 5. Rabbits compete with sheep for grazing. 6. By 1951 wool production reduced to 25% of what it was. 7. 1950 Myxoma virus introduced. Transmitted by fleas and mosquitoes 8. In 2 years covered all Australia 9. Initial virulence was 99.6%, by 1954 dropped to 85% - evolved an accommodation with host.

11. Floods of the Murray-Darling river Australia 1950

12. Biological control Australia European rabbits caused overgrazing. Controlled by the Myxoma virus causing myxomatosis. Carried by fleas and mosquitoes.

13. Decline in harvested rabbit skins after Myxoma virus spread through Australia in 1950

14. EXAMPLES OF SUCCESSFUL BIOLOGICAL CONTROL Insect pests: 1. Many insects brought in accidentally through human commerce 2. Into North America: 300 species from Europe 3. Into Europe: 34 species from N. America – not clear why the difference 4. Winter moth; i. From Europe, eats apple trees, oaks. In Vancouver Island. ii. Introduced 2 parasitic wasps that reduced the pest density

15. Winter moth in British Columbia after Introduction of parasites

16. EXAMPLES OF SUCCESSFUL BIOLOGICAL CONTROL Insect pests: 1. Gypsy Moth Lymantria dispar : introduced accidentally in Massachusetts 1869. Escaped from breeding cages. 2. Defoliate oaks, fruit trees, kills them. 3. Early attempts to eradicate used primitive chemicals – nearly succeeded but funds stopped as density declined. So outbreak again and spread across USA. 4. 1950s – aerial spray DDT 5. Natural enemies – 47 species introduced. None could stop spread since they have to stay behind the front line. 6. Chemical sprays make it worse because kill parasites before the moth. 7. Irradiated males – take the place of fertile males. Works in local areas 8. Artificial Pheromones – attracts males to false locations, local only 9. Biological viruses – spray over the infestation. Partially successful

17. Gypsy moth females depositing egg clusters on oaks, Massachusetts 1895

18. Spread of Gypsy moth (Lymantria dispar)

20. EXAMPLES OF SUCCESSFUL BIOLOGICAL CONTROL Weeds: 1. Weeds brought in with livestock food, or attached to trade goods. 2. Most are early succession species with high dispersal ability. 3. Established often due to disturbance due to human activity - especially agriculture, forestry and livestock grazing 4. Habitats most prone to invasion from disturbance are grasslands, and islands 5. Invasions often have long period of low density before rapid expansion 6. Low density is when eradication could occur but usually not noticed so chance is lost

21. Activities most likely to promote invasion of weeds • through disturbance of native vegetation • Agriculture/forestry are important • 2. Grazing livestock are important

22. Habitats most prone to invasion of exotic weeds • due to disturbance • Grasslands – transformed by agriculture • 2. Islands – prone to invasion

23. Patterson’s curse (Echium)exotic weed spread by rabbits

24. Three species of weed Echium spreading through Australia. Note the long period of early low density. Patterson’s curse

25. Opuntia cactus spread in South Africa – note the long delay before rapid spread

26. Illustrating spread- Japanese knotweed (Fallopia japonica) introduced to Britain In 1825. Vegetative reproduction, perennial weed grows up to 3 m. From Myers & Bazely 2003 Ecology & control of introduced plants. CUP.

27. Example of Biocontrol of weeds After biocontrol of the weed with the weevil Mecinus janthinus 2000 Dalmatian Toadflax in Southern B.C. 1997

28. Weed tree Acacia saligna, from Australia Invading tip of South Africa - Biological control using rust fungus Uromycladium

29. Opuntiastricta– • Prickly pear from • Mexico • Exotic weed in • Australia • Controlled by the • moth Cactoblastis • in the 1930s

30. Moth Cactoblastis used to control Prickly Pear Cactus in Australia

31. Biological Control of Diffuse Knapweed Caroline Jackson

32. Diffuse knapweed: the problem

33. Diffuse knapweed: the problem

34. Diffuse Knapweed • Introduced in 1907 to Washington State • Contaminant of alfalfa seed • Introduced to B.C. sometime before 1930 • Now infests more than 3 million acres in North America

35. Diffuse Knapweed: The Problem • Knapweed foliage contains a bitter compound • The surrounding more palatable vegetation is overgrazed, facilitating the spread of the knapweed

36. Biodiversity threat: Knapweed outcompetes and excludes native vegetation • Economic threat: Can reduce forage potential by 90% ($5 million annual loss for B.C. ranchers)

37. Diffuse Knapweed • Year 1 – seedling • Year 2 – rosette • Year 3 – flowerheads

38. Diffuse Knapweed: The Solution(s)? • Chemical control: Herbicide • Mechanical control: Hand pulling • Fire control: Flaming • Biological control: Natural enemies

39. Classical Biological Control • Import natural enemies to control exotics that have become established away from their place of origin

40. Classical Biological Control • Research in country of origin to find suitable bioagents • 10 agents have been introduced for diffuse knapweed in the past 3 decades

41. Gallflies: Urophora affinis and Urophora quadrifasciata Good dispersers (fly) Reduce seed production, BUT… No significant impact on adult plant density

42. Root boring beetle: Sphenoptera jugoslavica adult Along with gallflies, further reduce seed production Adults feed on rosettes and flowering plants; flowering is delayed. Bob Richard, USDA-APHIS-PPQ. larva larva Bob Richard, USDA-APHIS-PPQ.

43. Is it enough to reduce seed production? • The danger is that the plant may be able to compensate for losses in seed production through higher survival of later life stages

44. Diffuse knapweed: • Biological control with the weevil Larinus minutus

45. Most recent agent, Larinus minutus was introduced in 1996 • Larinus attacks both the seed and the vegetative portions of the weed

48. Biocontrol of Knapweed • Larinus minutus appears to offer the most promising control

49. Biocontrol of Knapweed With Weevils / Without Weevils

50. ECONOMIC BENEFITS In summary, if biological control works it can provide Considerable economic benefit while being Ecologically friendly. e.g. Patterson’s curse Biological Control through insects 1. Benefits to farmers reclaiming land = $30 million 2. Costs to bee-keepers = $2 million