La. Admin. Code tit. 70 § I-309

Current through Register Vol. 50, No. 11, November 20, 2024

Section I-309 - Factors of Herbicide Application

A. Herbicide Types

1. Soil-active (residual) herbicides are active in the soil and stop plant growth of germinated seeds and roots in the following manner. Soil-active herbicides are moved into the root zone by water. The herbicide is absorbed by the root system and translocated throughout the plant affecting plant growth processes. Visual effects should begin to appear in several days. The swiftness of the herbicide action is dependent on soil type, rainfall, plant species and rate of herbicide application. Soil-active herbicides can be applied to the soil in the winter prior to or shortly after the emergence of vegetation in spring. Vegetation must be present; never apply herbicide to already bare ground.

2. Contact herbicides halt visible plant growth at least for a short time in the following manner. Contact herbicides are absorbed by the foliage and transported throughout the plant, affecting plant growth processes. Several days are usually required for the effects to appear. Some of these herbicides may also have a short period of activity in the soil. Vegetative diversity may require a combination of chemicals to be used if broad-spectrum control is desired.

B. Desired Vegetation Control

1. Bare Ground or Complete Vegetation Control. Soil-active herbicide at the proper rate and time will normally provide complete vegetation control. Bare ground vegetation management may be desirable in areas where it can be economically maintained or where plant growth creates fire or other safety hazard or decreases maintenance efficiency. To maintain a bare ground condition after the first year application, spot-treatment may be necessary. Application of an excessive quantity of chemical is not economical and may result in damage to desirable vegetation. This type of treatment should only be used in storage yards.

2. Selective Weeding. Selective weeding is the use of a herbicide or a combination of herbicides for the control of selected species and does not permanently harm desired vegetation. Herbicides used for this type of control may be applied either as a per-emergence (before plants emerge from seed) or a post-emergence (after plants emerge from seeds) application.

3. Chemical Mowing. This is the practice of using herbicide to control undesirable vegetation in close proximity to valuable plants. This procedure can be used to control vegetation under fences and guardrails, along drainage ditches and in landscaped areas when near desirable vegetation.

C. Type and Species of Plants to be Controlled

1. Proper selection of herbicides and their application rates are dependent on the type and species of vegetation to be controlled as well as the condition of the plant. Some plant species are resistant to certain herbicides. The condition of a plant may be either active growth or dormancy. It may be a seedling or a mature plant or it may be budding, leafing, flowering or fruiting. All of these conditions should be considered when deciding where and when to use or not to use herbicides. For example, the best condition to apply a contact herbicide to many plants is when they are about to produce a seed head or fruit (e.g., the "boot" stage of Johnson grass). In general, seedling plants are easier to control than older more established plants. Plants are categorized as either annual, biennial or perennial.

2. Annual and Biennial Plants. These plants originate from seed. Annuals complete their life cycle in one year (seed to seed); biennials require two years to complete their life cycle. A contact treatment is generally sufficient in controlling seedlings. Annual weeds around signs and other appurtenances can be controlled with contact treatment or in combination with a pre-emergence herbicide.

3. Perennial Plants. These plants have an extensive root system and live from year to year. Perennials also produce seeds to ensure survival of their species. Specific herbicides, whether contact or soil active, are usually required for their control.

D. Soil Type. Depending on soil type, the proper application rate yields good vegetation control. Soil-active herbicides are more active in soils that are low in clay or organic matter because of the reduced absorbency of these soils. Therefore, the application rate may be reduced. In soils that are high in clay or organic matter, herbicide adheres to the soil particles and is not available to the roots of the plant. Consequently, the rate of herbicide application may need to be increased. The acidic/alkaline nature of the soil can also affect the performance of a herbicide. For example, in relatively acidic soils, oust decomposes at a faster rate than it does in more alkaline soils. In loose or sandy soils a soil-active herbicide may move off target easily carried, by either water or wind.

E. Wind Velocity

1. Wind will disturb the spray pattern and blow the chemical away from the target area; high winds can blow it several feet away. The wider the pattern the greater the effects of wind distortion. It is best to spray before wind velocity rises. The proper drift control agent will help reduce drift. If wind velocity rises too high, and the pattern cannot be kept on target, then spraying should be discontinued.

2. For purposes of deciding whether to spray and for record-keeping, carry a wind gauge in the spray unit to determine wind speed. Highest winds permissible will be 10 miles per hour.

F. Humidity. Relative humidity is the percentage of moisture in the atmosphere relative to the maximum amount which the atmosphere could hold. Generally, the higher the humidity at the time of application, the more rapid the uptake of contact applied herbicides. However, when humidity is at or approaching 100 percent, rainfall will most likely occur and the herbicide will be washed from the leaf surface. Consequently, herbicides should not be applied when rainfall is imminent. Conversely, if the humidity is approximately 60 percent or lower, the longer it may take the herbicide to become active.

G. Rainfall

1. Rainfall affects chemical control of vegetation. It is a vehicle for movement of soil-active herbicides into the root zone of plants. Soil-active chemicals must be in solution before they can enter the root system of plants. Excessive water may reach the soil-active herbicide below the root zone of the plant resulting in poor control. Moisture from rainfall, thawing cycles and snow on the ground may prevent the herbicide from entering the soil in sufficient quantities to achieve the desired degree of control. Moreover, excessive rainfall may lead to serious herbicide damage to areas outside of the target area.

2. Do not spray contact herbicides during rainfall or if rainfall is likely to occur within six hours after application. Rain will wash the herbicides off the leaves before it can be absorbed by the plant. After a rain, dust on the leaves will have been washed off and contact herbicides are more easily absorbed by the plant. Allow the foliage time to dry after a rain before spraying since wet foliage may yield poor results.

H. Temperature. Temperature affects the results of vegetation control with herbicides. Do not use herbicides when the soil is frozen, when rain or snow is falling, or when there is snow on the ground. High temperatures during the summer months may cause many plants to become semi-dormant. When this occurs the plants will not absorb the herbicide adequately.

I. Water Quality. Use good clean water to mix herbicides, as impurities in the water may deactivate the herbicide. Another reason for using clean water is that sand or clay particles may damage the pump, solenoids and nozzles of the spray rig.

J. Mixing, Timing and Application

1. Mixing and application are to be in conformance with the manufacturers' recommendations. All precautions issued by the manufacturer are to be taken into account and followed.

2. Timing for spraying of herbicides will be coordinated and determined by the roadside development district coordinator and the parish maintenance superintendent.

3. A spraying report is to be filled out by the herbicide applicator when applying herbicides to the roadsides.

4. Following is a chart of herbicides, application rates, times to spray and pertinent comments concerning their uses.

K. Herbicide Rate Chart

Herbicide Rate Chart
Product Name	Rate per Acre	500 Gallon Tank Mix	1,000 Gallon Tank Mix	Nov. & Dec.	Jan. & Feb.	March & April	May to Oct.	Comments
Oust	1 oz. 1\2 oz. 2 oz.	16 oz. 24.oz. 32 oz.	32 oz. 48 oz. 64 oz.	X	X X			2 ounce Oust to be used where Oust is 1 ounce required to be used in Nov. & Dec., 2 ounce to be used in Jan. & Feb. In areas where there is heavy concentration of Johnson Grass, 1 1/2 ounce per acre should be used. On moderate stands of Johnson Grass, 1 ounce should be used after Johnson Grass has almost been eliminated. Oust should not be used where Bahia is predominant.
2-4-D Roundup	2 qt. 1 pt.	8 gal. 2 gal.	16 gal. 4 gal.			X	X X	Combination of 2-4-D and Roundup should be used only in southern part of state where 2-4-D is not restricted, and when temperature reaches 75 ° F or above. Can be used around signs and guardrails at rate of 2 quart 2-4-D and 1 quart Roundup per acre. do not spray this rate on slopes .
Garlon 3A Roundup Pro	1 qt. 1 pt.	4 gal. 2 gal.	8 gal. 4 gal.			X	X	Only to be used in northern part of state where 2-4-D is restricted and when temperature reaches 75 ° F or above. Can be used around guardrails and signs at the rate of 1 quart Garlon and 1 quart Roundup.
M.S.M.A. 2-4-D	2 qt. 2 qt.	8 gal. 8 gal.	16 gal. 16 gal.			X	X	Only to be used in southern part of state where 2-4-D is not restricted, and on very rare occasions where Roundup will not do as good a job, and where there is a very thin stand of Bermuda grass.
M.S.M.A. Garlon 3A	2 qt. 2 qt.	8 gal. 4 gal.	16 gal. 8 gal.			X	X	Only be used in southern part of the state where 2-4-D is restricted, and on very rare occasions where Roundup will not do as good a job, and where there is a very thin stand of Bermuda grass.
Campaign	48 oz.	6 gal.	12 gal.			X	X	Can be used in southern section of state in lieu of 2-4-D and Roundup mixture. When heavy concentration of vines and woody plants, add 1 pint of 2-4-D.
Escort	1/2 ounce	8 oz.	16 oz.			X	X	Can be used where 2-4-D is restricted.
Rodeo	1 pt. 1 qt.	2 gal. 4 gal.	4 gal. 8 gal.			X	X	To be used on slopes and in water where Bermuda grass should not be destroyed. To be used under bridges and in water for complete control of vegetation.
Roundup Pro	2 qt.	8 gal.	16 gal.			X	X	To be used on shoulders, around Guardrails and signs when temperature reaches 70 ° F or above. Can be used close to trees.
Hyvar XL	10 gal.	120 gal.	320 gal.	X	X			Only to be used in storage yards and in places where complete soil sterilization is required. Can not be sprayed close to trees where there is danger of runoff.
Surfactant	8 oz.	1 gal.	2 gal.					To be used in all tank mixes except Oust alone, Hyvar XL, or Roundup Pro.
Poly Vinyl	2 oz.	1 qt.	2 qt.					To be used in all tank mixes where fixed booms are used.
Recommended Speed and Pressure on Cibolo sprayers, Guide to Calibration Pressure: 28 pounds - 10 mph Rate Tank Mix Gallon Per Acre: 31.25 Acres: 500 gallon Tank mix - 16 Acres Acres: 1000 gallon Tank mix - 32 Acres

L. Daily Herbicide Spraying Report

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La. Admin. Code tit. 70, § I-309

Promulgated by the Department of Transportation and Development, LR 17:204 (February 1991), amended LR 26:1658 (August 2000).

AUTHORITY NOTE: Promulgated in accordance with R.S. 47:820.6.