Herbicides and Their Use

herbicide

chemicals used to control, or eliminate weeds by disrupting normal plant functions

selective herbicides

chemicals that eliminate certain plant species with little or no damage to desirable plant species

non-selective herbicides

chemicals that are toxic to all plants and used to remove many species of plants from an area

plants are best controlled during this time when they can absorb and move the herbicide around the plant...

actively growing and can absorb and move the herbicide

preemergence herbicides

herbicides applied before weeds germinate and prevent the germinating seeds from establishing in the soil

postemergence herbicides

herbicides applied to actively growing plant foliage

mode of action

chemical interaction of the herbicide that interrupts a biological process needed for plant growth

action site

the location in the plant where the herbicide interrupts a biological process

several requirements for herbicides to work include...

adequately contact the plants, capable of being absorbed, move within the plants to the action site, reach toxic levels

Translocated (systemic) herbicides

herbicides that move through the entire plant system in both the water stream (xylem) and the food stream (phloem)

contact herbicides

controls weeds by direct contact with plant parts, but only controls the plant parts it is in contact with

residual herbicide

applied to the soil before planting and requires moisture and soil microbes to break down the chemical over time to extend the usefulness

LAW

the information on a pesticide label is for the safest and most effective use of the product and when it comes to herbicide application, the pesticide label is the...

foliar application

applied directly to the leaves so that the herbicide is absorbed into the plant and carried down to the roots

band spraying

applied to a narrow strip over the crop row and avoids bare soil when possible to minimize overspray

spot treatments

products are designed for homeowners and gardeners to apply to small, weed-infested areas within a field

ground application

broadcast spraying a solution to the soil uniformly over the entire area

directed spraying

this application method sprays herbicide between the plant rows with no herbicide applied to the foliage because the action site for the herbicide is the roots...

adjuvants

substances added to a herbicide mixture to improve herbicidal activity or application characteristics

adjuvants provide several different types of performance enhancements to improve herbicides application including...

surfactant to hold the spray on the leaf, regulating pH, keeping water/herbicide combination properly mixed, minimizes drift

surfactants

adjuvant used with herbicides to help it spread over a leaf surface and penetrate the waxy cuticle of a leaf

to work well herbicides require this type of weather

most effective in warm temperatures and good relative humidity

drift

the movement of a pesticide through the air to an unintended (off-target) site

physical drifts

occurs during application when spray droplets move away with wind before reaching the intended spray target

vapor drift

occurs only with certain herbicides that are easily volatilized (evaporate easily) and move freely with the air

while proper soil pH benefits herbicide application to plants, the use of this will actually chemically weaken herbicides...

large amounts of organic matter