| 1.0 | Purpose |
| Soil conditions vary from area to area. Where problems exist, it may be necessary to sterilize the soil. If so, the owner and/or contractor should recognize the problem and proceed with corrective treatment. These Guidelines will serve to aid in determining when soil sterilization is necessary and offer methods for rectifying problems caused by vegetation. |
| 2.0 | Scope |
| These Guidelines cover causes of vegetation growth, methods of control including the use of herbicides, possible side effects resulting from the use of herbicides, degree of need, and the economic factors in any soil sterilization program. For further information on soil investigation, see guideline I.B. Site Investigation. |
| 3.0 | Soil Conditions |
| The owner or contractor should always determine whether soil conditions make sterilization necessary or desirable. Adjacent pavements, whether sealed or not, provide good indications of possible need for treatment. Tennis courts and running tracks that are two or more years old also attest to the problem if it exists. Where necessary, take soil samples at various levels from the surface down to a point below the subgrade of the proposed track or court and down to the depth of the root zone. These samples should be sent to a soil laboratory to determine whether the potential for weed growth warrants sterilization. |
| 4.0 | Possible Conditions of Growth |
| There are three main causes for vegetation growth under and through a surface: | 1. | Excavation cuts existing vegetation growth but does not entirely eliminate it. Tree roots extending under the court or track area must be neutralized or removed prior to construction. (There are commercially available products which inhibit root growth). | | 2. | Excavation uncovers ungerminated seeds but does not remove all of them. After construction is complete, these dormant seeds are more apt to germinate due to the likelihood of increased moisture in the soil and warmer soil temperatures. This is particularly true with asphaltic-concrete construction. Note: when a coating is applied to these pavements, it serves as a barrier to filtration of surface water. Also, it reflects rather than absorbs more of the sun’s heat, thus reducing the incidence of germination. | | 3. | Fill materials brought in to raise the subgrade or backfill excavations and trenches may contain ungerminated seeds and/or the live root sections of weeds. | |
| 5.0 | Use of Herbicides |
| | A. | General | | Herbicides suitable for vegetation regrowth prevention come in liquid, pellet and powder form. Liquid herbicides are mixed with water to facilitate application. A water mixture is designed to permit root systems to absorb the herbicide. Herbicides in pellet form are useful where rainfall is sufficient to carry them to root systems. Herbicide manufacturers publish dosage rates for effective weed control. Heavier applications usually provide longer residual effects; however, strict adherence to manufacturers’ recommendations is advised. | | B. | Under Pavement | | If vegetation control is required, the owner, contractor or a designated subcontractor can apply liquid, powdered, or pelletized herbicide to the subgrade before installing the concrete or asphaltic-concrete pavement. | |
| | C. | Cautions | | | 1. | Apply herbicides, in any form, in strict accordance with the label instructions. The label provides complete specifications regarding the chemical content and directions for use of the herbicide. It is important to read the label carefully and then precisely follow instructions to assure the effectiveness and safety of the process. | | 2. | After treatment is complete, it is important to pave the subgrade as soon as possible. If rain or surface water washes into the excavation, or enters it through a porous stratum such as an uncovered stone base or an unsealed asphaltic-concrete surface, there is a strong possibility that the herbicide will leach or wash into the surrounding ground, causing possible harm to desirable plant growth. | | 3. | It is advisable to plant new vegetation, such as trees, shrubs, and flowers, sufficiently far from the sterilized area to protect their root systems from becoming contaminated by the herbicide. | | 4. | Liquid herbicides can be carried by the wind during application. Should this occur, it could severely damage vegetation adjacent to the construction site. Never attempt to apply liquid herbicides when there are strong breezes or when rain is imminent. | | 5. | Do not apply liquid herbicides to water-saturated soils such as may exist after a rainfall. | | |
| 6.0 | Track and Tennis Court Maintenance |
| | A. | Crack Treatment of Existing Tennis Courts and Tracks
The same herbicides that are used in new construction can be utilized in the patching and/or sealing process for existing hard-surfaced tennis courts and tracks. Since cracks are sites for possible weed growth, they should not be repaired until the potential for such growth is eliminated. If there are weeds in the cracks, apply liquid herbicides before removing them. This allows the herbicide to enter the weeds through both the foliage and the root system. After an appropriate time, which depends on the herbicide used, remove the weeds, all dirt, and other foreign material from the cracks. Apply a second dose of herbicide to the crack areas just before patching or sealing them. It is essential, however, to determine beforehand whether application of the herbicide will prevent such patches from adhering properly to the treated areas. | | B. | Surface Patching
Low areas, such as birdbaths, are possible sites for growth of weeds, algae or fungus. For weeds, it may well be advisable to apply liquid herbicide to these areas before surface patching. For algae or fungus growth, apply a diluted solution of liquid bleach (1 part bleach to 5-7 parts water); then, scrub the surface to remove algae or fungus. It is essential in either case to determine beforehand whether application of the herbicide or bleach will prevent patches from adhering properly to the treated areas. | |
