• Selection • Application Chemical controls • Contact/Absorption/Uptake • Metabolization /Chemical reaction • Plant death/Reduction in vigor • Chemical breakdown of the in the environment

Round-up Label

http://www.afpmb.org/pubs/standardlists/labels/6840-01-108-9578_label_roundup_pro.pdf

Surfactant How do herbicides work?

• Growth regulators • Photosynthesis inhibitors • Pigment inhibitors • Seedling growth inhibitors • Cell membrane disruptors and organic arsenicals • Lipid synthesis inhibitors • Amino acid synthesis inhibitors • Indiscriminant amino acid synthesis inhibitors Surfactants are compounds that lower the surface tension of a liquid, the • Toxic to life chemicals interfacial tension between two liquids, or that between a liquid and a solid. Surfactants may act as detergents, wetting agents, emulsifiers, foaming agents, http://www.wssa.net/Weeds/Tools/Herbicides/HerbicideMovies.htm and dispersants. http://en.wikipedia.org/wiki/Surfactant http://stephenville.tamu.edu/~butler/foragesoftexas/weedcontrol/hermode.pdf

1 Growth regulators Photosynthesis inhibitors

• Inhibit photosynthesis • Disrupt the hormonal balance that regulates mostly in broadleaved processes such as cell plants + a few annual division, protein grasses. synthesis, and respiration. • Leaves turn yellow • Stems curl, twist, and then brown droop. • Foliar, pre-, and post • Leaves cup, crinkle, and emergence have irregular edges. • Usually applied to foliage but also effective in soil.

http://www.btny.purdue.edu/weedscience/moa/Auxin_Growth_Regulators/movie/CLARITY.html

Pigment inhibitors Seedling growth inhibitors

• Destroy chlorophyll by • Applied to the soil, has preventing formation short active period • Works on small seeded of carotenoids. forbs and grasses • New leaves are white • Root inhibitors interrupt or yellow. cell division – Absorbed through roots • Absorbed by roots – Large seeded plants can and translocated to push roots through the treated zone and survive. shoot tissue. • Shoot inhibitors interrupt cell growth – Absorbed through shoots http://www.btny.purdue.edu/weedscience/moa/Cartenoid_pigment_inhibitors/movie/CLOMAZONE.html – Large seeded plants can wait until effect wears off

Cell membrane disruptors and Lipid synthesis inhibitors organic arsenicals • Destroy cell membranes • Only works on actively and cause the plant to dry growing annual and out perennial grasses, not on • No root effect, only works broadleaf plants where contacts plant • No soil activity • Works best on annuals • Absorbed within an hour • Usually applied to foliage – rain won’t wash it off • No symptoms for 7-14 days • Systemic effect.

2 Indiscriminant Amino acid Amino acid synthesis inhibitors synthesis inhibitors • used at extremely low • Non-selective and control rates, a broad range of annual and perennial grasses, • controls both grasses and broadleaves and sedges. broadleaf plants, • Plants treated with systemic or sulfosate • has soil and foliar activity turn yellow in 5 to 7 days, • essentially non-toxic to then turn brown and die mammals and most in 10 to 14 days. nonvegetative life forms. • acts more quickly, in 3 to 5 days. • Species specific • Not toxic to animals

Toxic to life chemicals Agent Orange

• Motor oil, diesel fuel, acid, bleach, • Came in orange-striped barrels acetone, soap, salt, etc. • a roughly 1:1 mixture of two phenoxy herbicides in ester form, 2,4- dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5- T). • Kills broad leafed plants • 2,4,5-T is now banned in the US (since the late 80s)

Safety issues Herbicide application

• Spraying onto foliage • Wiping onto stems or trunk • Spraying basal bark or stumps • Injecting into sap wood • Using soil application

http://www.dem.ri.gov/programs/bnatres/agricult/pdf/frup.pdf

3 Mechanism, uptake and plant properties • What does the herbicide do? • Where is the herbicide taken into the plant? • What does the target plant look like where you want it to take up the herbicide • What are the other things that will be affected?

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