Chapter 5 - Herbicide Technology

Chlorsulfuron

Amino acid inhibitor

Glyphosate

Amino acid inhibitor

Imazapyr

Amino acid inhibitor

Amino acid inhibitors

Are translocated throughout the plant.May be nonpersistent such as glyphosate. Glyphosate is nonselective and must be absorbed through the leaves.May be persistent such as chlorsulfuron, metsulfuron-methyl, sulfometuron, and imazapyr. They are taken in through the leaves and roots. Imazapyr and sulfometuron control many grasses and herbaceous weeds. Chlorsulfuron and metasulfuron-methyl are less effective on most grasses. May take a week to several weeks before symptoms appear following their application, although plant growth stops soon after application.Are used at low rates - ounces per acre.

2,4-D

Auxin growth regulator

Aminopyralid

Auxin growth regulator

Triclopyr

Auxin growth regulator

Photosynthesis inhibitors

Block photosynthesis is susceptible plants. They have no direct effect on root growth, although root uptake is the primary route for these herbicides to enter the plant. Persist in the soil and provide residual weed control. Length of persistence varies with each herbicide and depends on the amount applied, soil type, and climate.

Fosamine

Bud development inhibitor

Contact vs. translocated.

Contact - herbicide that kills only the parts of the plant it actually touches vs. translocated - herbicide that is absorbed by roots or leaves and carried in the plant sap throughout the plant; also referred to as systematic herbicides.

Herbicides that affect cell membranes and walls

Diquat and paraquat are nonselective contact herbicides. Injury may be visible a few hours after application. Plants can recover from incomplete spray coverage. Dichlobemil and indaziflam are inhibitors of cellulose biosynthesis, the primary structural component of plant cell walls. These herbicides inhibit germination and new cell growth at the growing points of roots and shoots. For R.O.W., they have practical uses for soil-applied nonselective vegetation control beneath asphalt in areas such as parking lots, roads, railroads, and roadsides.

Bud development inhibitors

Fosamine inhibits bud development when applied to woody plants late in the growing season, but before leaves start changing colors. Except for pines, there is little or no visible brownout until the following spring when susceptible woody plants do not resume growth. Fosamine move only from leaves to buds, so uniform coverage is necessary. Has no soil activity and does not inure grasses at normal use rates.

Indaziflam

Herbicide that affects cell membranes and walls

Chemicals used for killing plants or severely interrupting their normal growth process.

Herbicide.

Root development inhibitors

Herbicides that prevent seedling root development, stop the growth of roots and shoots of germinating seeds or small seedling by disrupting cell division. Pendimethalin translocates to only a limited degree in plants, it seldom controls established weeds, highly selective for grass control and usually does not leach in soils, effective control depends on sufficient rainfall soon after application or soil incorporation.

The way in which a particular herbicide disrupts a target plant process.

Mode of action.

Auxin growth regulators

One of the common symptoms of these herbicides is distorted growth including twisting and curling. Translocate throughout the plant and are usually applied to foliage. Can cause distorted plant growth at low rates. Drift to susceptible crops, such as cotton, grape, peppers, and tomatoes, is a concern. Are available in liquid forms as water-soluble salts and oil-soluble esters. Are effective for controlling many broadleaf weeds and trees.

Persistent vs. nonpersistent.

Persistent - herbicide that remains active in the environment for an extended period of time vs. nonpersistent - herbicide that is short-lived in the environment because it is broken down or becomes so tightly bound to soil that they are not available for plant uptake.

What is the term for herbicides that remain active in the environment for an extended period of time?

Persistent.

Hexazinone

Photosynthesis inhibitor

Preemergence vs. post emergence.

Preemergence - root-absorbed herbicide that is generally more effective when applied before weeds emerge from the soil vs. post emergence - Foliage-absorbed herbicide that is generally more effective when applied before weeds emerge from the soil.

What is the term for herbicides that are generally most effective when applied before the weeds emerge from the soil?

Preemergent.

Describe how the public can be assured that herbicides used on rights-of-way will not be harmful to human health if used correctly.

Public information program that both addresses the reason for removing vegetation and answers potential questions concerning safety of herbicides should be a part of any vegetation management program. This is part of the education component that right-of-way managers should bear in mind when approached by members of the general public.

Pendimethalin

Root development inhibitor

Name and describe two major reasons for using plant growth regulators along rights-of-way.

Seedhead suppression of roadside grasses to reduce mowing and to reduce sprout growth after line clearance trimming on electric utility rights-of-way. May also be effectively used for roadside turf maintenance along guard rails, mile-marker delineators, signposts, and in ramp and merge areas.

Selective vs. nonselective.

Selective - herbicide that controls only certain types of plants but causes minimal or no injury to other plant types vs. nonselective - herbicide that generally controls most plants and is used where complete control is desired.

What is the term for herbicides that control only certain types of plants?

Selective.

In general, how do plant growth regulators (PGRs) function?

They inhibit cell division and elongation

What is the term for herbicides that are absorbed by roots or leaves and carried in the plant sap throughout the plant?

Translocated (systemic).

How is the public ensured that they will not come on contact with herbicide concentrations that may cause harmful effects?

Use restrictions for all pesticides are written into product labeling.