AGR 3102 (1) Principles of Weed Science Herbicides

1. AGR 3102 (1)Principles of Weed ScienceHerbicides Muhammad Saiful Ahmad Hamdani

2. Week 7 – Topics Covered Herbicides: Introduction to herbicides History, nomenclature, toxicity, classification

3. Introduction to Herbicides • Any chemical agent that kills or greatly inhibits plant growth. • “Plant killer". Herbicides specifically cause phytotoxicity to plants. • Phytotoxicity: the degree of toxic effect by a compound on plant growth.

4. Why herbicides are less harmful to us and animals? Herbicides target highly specific biological or biochemical processes within plants (i.e. PS, branch-chain amino acids synthesis, plant enzyme & hormone, etc). At label rate, have very little impact on non plant or non-photosynthetic organisms. Still, not safe to intentionally ingest herbicides (still have toxic effect, different formulation, mixed with other potentially dangerous chemicals too i.e. adjuvant). Paraquat is exceptional!!!

5. 1. History of Herbicides 1890 to 1900 - sodium arsenite to control aquatic plants in waterways in the US. 1925 - sodium chlorate (direct soil application) was first used for killing weeds. 1934 - sodium nitrocresylate, as the first selective weed killer in France.

6. 1940s – first organic herbicide 2,4-D was commercialized providing selective control of certain broadleaf weeds in grass crops. 1960's – pre-emergence herbicides trifluralin and atrazine introduced. 1974 - glyphosate (Roundup) available - among the world’s most important herbicides -S.B.Powles. Control broad-spectrum of weed spp. As in 2011, more than 200 herbicides from 22 mode-of-actions available in the market.

8. Why Herbicides Are Important Component in Agriculture??? Pesticide expenditure totaled more than $39.4 billion in 2007. Expected to increase 2.9% per year to $52 billion in 2014. Herbicides make up the largest number of products and are the most used in the agricultural sector, due to their extensive use. Worldwide, expenditure on herbicides account40% of all pesticide expenditures (Grube et al. 2011).

9. Malaysia: 75-80% herbicides use & 70-75% trade compared to other pesticides (FAO, 2013).

10. Examples of herbicide in Malaysia 15

11. Why Herbicide Use is Always Higher Than Other Pesticides? We human don’t want crops and weeds to co-exist

12. Herbicide Nomenclature Active ingredient (AI) - the chemical in the herbicide formulation primarily responsible for its phytotoxicity. Kills/injures the plant/weed. Trade name - a trademark or other designation by which a commercial product is identified. Registration no., registrant/distributor included. Common name - each herbicidal chemical has one common name assigned to it. In many cases, the common name is a simplified version of the chemical name.

13. 4. Chemical name - the systematic name of a chemical compound according to the rules of nomenclature of the International Union of Pure and Applied Chemistry (IUPAC), Chemical Abstracts Service (CAS) or other organization. Represents AI. 5. Toxicity class – how dangerous of a herbicide to animals/humans. 6. Formulation & type of herbicide – form/condition of the herbicide. Mixing instructions & procedures prior application included.

14. Common name

15. Acute toxicity(death) studies of a herbicide on non target population(non photosynthetic) Experiments on animals, via oral, inhaled, or external application of a herbicide. Test was created by J. W. Trevan in 1927. Herbicide Toxicity Class

16. Source: Richards, Kerry Penn State University Extension Service

17. Source: Richards, Kerry Penn State University Extension Service

18. LD50 Lethal Dose = Amount of chemical it takes to kill 50% of an experimental population

19. LD50 value measurement: mg chemical/kg of test population Draw back: not address issues of other potential harm of the agent, such as bioaccumulation, issues of carcinogenicity, mutagenic effects, or the impact on reproduction.

20. Source: Richards, Kerry Penn State University Extension Service

22. Table 2. Comparison of oral LD50 values for commonly used herbicides and consumer goods. Source: Fishel et al. 2009

23. Important!!! Some herbicides such as paraquat are extremely harmful and must be handled with great care. However, just because some herbicides are less toxic does not mean that any herbicides should be handled carelessly. Using a herbicide in accordance with the product label will not often result in personal injury or cause for alarm.

24. Herbicide Classification Classified based on different activity, mode of action, residual activity, placement, time of application, methods of application, & type of vegetation controlled (selectivity).

25. A. Selectivity: Selective vs. Non-selective 1. Selective: toxic to some species and much less toxic to others at the label rate. Kills weeds but not the crop at label rate. 2. Non-selective/broad-spectrum: kills or severely damages all or most species. A non-selective herbicide kills weeds and potentially crops. Must avoid contact with crops!!! A selective herbicide can be made non-selective by applying improperly or by applying high rates. Selectivity is usually rate dependent.

26. Herbicide Selectivity Non Selective/ Broad Spectrum: A herbicide that controls many plant species. Selective: A herbicide that is more effective in controlling some plant species than others. No activity No activity Activity 26

27. B. Activity: contact vs. systemic 1. Contact herbicides a. Effective only on tissue contacted by herbicide. b. Very little movement within the plant. c. Full spray coverage is crucially essential. d. Usually exhibit acute effects. e. Effective on annuals, less for creeping perennials.

28. 2. Systemic herbicides • Absorbed by roots or above-ground parts, translocated within plant. • Good spray coverage is necessary, but less critical than contact herbicides. • Usually exhibit chronic effects. • Effective on annuals, as well as on perennials.

29. Effect of different activities of herbicideon Asystasia spp. in rubber plantation 3 weeks after spraying Paraquat: contact Glyphosate: systemic

30. C. Residual activity: Residual vs. Non-residual 1. Residual: Herbicide remains in active form in soil & retains activity on weeds growing after application. 2. Non-residual: Has activity only on weeds present at time of application. Become invalid upon reaching soil. Does not provide control of weeds that emerge after application.

31. D. Time of application (when herbicide is applied) Pre-plant: applied to soil prior to planting the crop. Incorporate or not. Pre-emergence: applied to the soil prior to emergence of the weed. Post-emergence: applied after emergence of the crop or/and weed.

32. Time of Applications = Weed Seed To the crop & weed To the weed Preplant Postemergence Preemergence To control emerging weeds after crop emerges After crop is sown but before crop or weeds emerge = Crop Seed OR Before the crop is planted After crop and/or weeds emerge 32

33. Two primary placement options for herbicides: E. Placement of herbicide Soil Application Foliar/Plant Application

34. F. Methods of application Refer to the ways herbicides can be applied. Several methods depending on herbicide, cropping system, crop/plant, & area:

35. Banding: • Application directly to a strip over or along a crop/crop seeds row. • Pre-emergence and post-emergence herbicides. • Targets weeds underneath/in crop canopy.

36. Broadcast/overall: • Uniform application to entire area/field/farm. • Pre-emergence and post-emergence herbicides. • Needs high amount of herbicides.

37. Directed: • Spray to the base of the crop, avoiding contact with foliage and green stems. • Post-emergence. • Need shield (hooded spray) in narrow rows.

38. Spot treatment: • Applying small amounts of herbicides to individual or small patches/groups of weeds. • Post-emergence. • Suitable in small areas.

39. Wiping technique: • Variation to spot treatment. • Mainly used in ornamental areas. • Just wipe the weeds when they are taller than the ornamentals. • Use rope, paint roller, or sponge type devices instead of nozzle.

40. Conclusion Herbicides = kill unwanted plant if use properly & appropriately. Kill crops, beneficial plants & even us if misuse. Most used compared to other pesticides. a.i. kills the weed, LD50 indicates the toxicity level to humans and animals, the lower LD50, the higher toxicity. Can be distinguished by different classifications. Know herbicide classification, can decide the most appropriate herbicide to apply & how to apply = avoid/minimise risk to us, crops and environment.