AGR 3102 Principles of Weed Science Herbicide Muhammad Saiful Ahmad Hamdani

Units 7 & 8 – Topics Covered Herbicides: Activity, Persistence and Residues in Soil Carryover Safety Guidelines

Herbicides Activity, Persistence and Residues in Soil Herbicides, upon contact with the soil are subject to various processes. These processes regarded as “environmental fate” of herbicides. Can affect the activity, efficacy and behaviour of the herbicide.

Also determine herbicides persistence in the soil. Herbicide soil persistence or residual life is the length of time a herbicide remains active in soil. Often stated as herbicide half-life: a measure of how long it takes for 50% of a chemical to degrade.

Micro-organism Decomposition Mainly are algae, fungi, and bacteria. They use all types of organic matter, including organic herbicides. Some chemicals are easily decomposed and some not. Chemical Decomposition Destroys herbicides through interaction with the soil constituents of oxygen, hydrogen or water (i.e. via oxidation or hydrolysis).

Adsorption by the Soil Herbicides adsorbed by clay and OM particles making the herbicide unavailable for uptake by the weed. High adsorption in soils high in OM and clay than sands. Results: the chemical is not effective as a herbicide.

Leaching The movement of herbicides through soil by water. Usually happens following rain or irrigation water after herbicide application. Water-soluble herbicides are most easily leached. Double-edged sword: effect weed control effectiveness, crop injury, herbicide carryover, and environmental problems. Herbicide carryover problem is lessened when leaching happens, but problem with underground water pollution.

Volatilization Herbicides may evaporate and be lost to the atmosphere as volatile gases. Vary from one to another. Herbicide volatilization increases as the temperature rises.

Photodecomposition Degradation of herbicides by sunlight. In the photodecomposition process, the herbicide molecule absorbs energy from sunlight, causing chemical reactions that result in herbicide inactivation. Many soil incorporated herbicides are light sensitive to sunlight.

Plant Uptake The uptake of herbicides by plant (crops or weeds) roots results in their removal from the environment; hence, reduced concentrations in the soil. Surface Runoff A herbicide may leave the application site in surface water running off the site. The herbicide may be dissolved or suspended in the runoff water or it may be adsorbed to soil carried by runoff water. A serious concern because runoff water ultimately makes it way into rivers and surface reservoirs used for drinking water.

Herbicides Carryover The concern is that herbicides applied this year/season may carry over and injure small plants lined out the following year caused by the high persistence in soil. Herbicides with residual activity/high soil persistence are like a double-edged sword. We want them to persist for several months in order to suppress weeds. Yet, we don’t want them to persist too long so that they interfere or injure crops planted the following year/season. Great if we can have herbicides that can last throughout crop growing period, then self destruct instantly before the next planting season. Well in reality it’s not going to happen…

Guidelines To Avoid Carryover Problems: 1)Calibrate the sprayer and apply herbicide accurately and uniformly: avoid overspray. 2) If incorporating, make sure it is done thoroughly and uniformly 3) Consider applying reduced rates of a persistent herbicide in combination with a less persistent herbicide. 4) Apply herbicide as early as possible and delay planting of the follow crop if carryover is suspected.

Safety Guidelines in Using Herbicides Herbicide Labels and Safety Guidelines Contains all information on the herbicide. Important for effective use from herbicides and safety to environment. Info provided: 1Product information 2Use information

3Safety information -Child Hazard Warning: All pesticide labels must bear the statement ”KEEP OUT OF REACH OF CHILDREN”. -Signal Words: DANGER, POISON, WARNING, CAUTION. -Hazards to Humans and Domestic Animals -Personal Protective Equipment (PPE) Statements: wearing personal protective equipment listed on the label: minimize your exposure.

PPE

The Correct Personal Protective Equipment

4Statement of Practical Treatment These statements tell you the first aid treatments recommended in case of exposure or poisoning. Typical statements include: -In case of contact with skin, wash immediately with plenty of soap and water. -In case of contact with eyes, flush with water for x minutes and get medical attention. -In case of inhalation exposure, move from contaminated area and get medical attention. -If swallowed, drink large quantities of milk, egg white, or water -- do not induce vomiting. -If swallowed, induce vomiting.

5Physical or Chemical Hazards These statements will tell you of any special fire, explosion, or chemical hazards the product may pose. For example: -Flammable: Do not use, pour, spill, or store near heat or open flame. Do not cut or weld container. -Corrosive: Store only in a corrosion- resistant tank.

6Environmental Information Herbicides may be harmful to the environment. Some products are classified as RESTRICTED USE HERBICIDE because of a potential environmental hazard. Watch for special warning statements on the label concerning hazards to the environment. For example: -This product is highly toxic to bees. -This product is toxic to fish. -This product is toxic to birds and other wildlife.

Summary Read the label before purchasing the herbicide, to determine: -whether this is the herbicide you need for the job. -whether the herbicide can be applied using the application equipment available. Read the label before you mix the herbicide to determine: -necessary protective equipment for safe handling. -what you can mix with the product (compatibility). -how much product is required. -the proper mixing procedure.

Read the label before applying the herbicide to determine: -safety measures necessary. -when to apply. -where the herbicide can be used (railroads, rights-of-way, non-crop areas, industrial sites). -how to apply. -restrictions of use. Read the label before storing or disposing of the herbicide and container, to determine: -where and how to store. -how to properly clean and dispose of the container.

Handle Herbicides With Great Care..... Care about yourself Care about people working with you Care about the crops Care about other organisms Care about your environment