1993 Proceedings of the Midwest Oak Savanna Conferences
HERBACEOUS WEED CONTROL IN ECOLOGICAL RESTORATIONS: AN ANALYTICAL APPROACH TO THE USE OF HERBICIDES
The decision to use herbicides as a method of weed control should only be made after careful examination of several issues. The target species must first be analyzed as far as its life cycle, growth pattern, and physical characteristics. The overall quality of the site must then be considered, along with the density of the target species.
Once these biological factors have been assessed, alternative control methods should be given priority over herbicide use. Examples are burning, mowing, scything, and hand pulling. These alternatives will need to be evaluated in light of the work force availability.
When considering herbicide use within this framework, investigation should be made into the allowable herbicides and their chemical modes of action. Only when all of these issues have been examined, can you determine the optimum control method.
Depending on the circumstances, the word "weed" has varying definitions. Generally, it is a plant living where it does not belong. For the purpose of ecological restoration, a weed is defined as a plant that is out of place and grows in profusion. It crowds out native species and possibly may form a monoculture. It is generally alien, but may be an opportunistic native which thrives in disturbed areas.
The proper place of herbicides in the control of weeds is best enunciated by the Illinois Nature Preserves Commission: "Herbicides should be limited to situations in which no other reasonable means of control are available."1
To apply this standard, certain characteristics of the plants and the site should be ascertained. Once the plants and site are understood, then available alternative means of control can be considered.
A plant's characteristics will help us to determine whether it will be a long-term problem and what control method to use on it. Specifically, we need to look at a plant's life cycle, its growth pattern, and its physical characteristics.
Site characteristics must also be taken into consideration when determining an appropriate method to control weeds. First, how many plants of a specific species are involved? Are you dealing with 500 or 5000? If the number is large, then strong consideration must be given to the timing necessary for the most effective control. If this window is relatively small, then the attack must be carried out with a method whereby many plants can be handled in a short period of time.
Next, what is the density involved? A plant that has already formed or is close to forming a monoculture might be effectively controlled by mowing (e.g., white sweet clover). If plants are spaced every 5 feet or every 50 feet then a hand control method would be more appropriate.
Site characteristics also include the assessment of the general quality of the surrounding flora. Is the area predominantly covered with other exotic species, or is it an area where native plants are in the majority? More conservative methods (i.e., ones less damaging to the surrounding flora) should be chosen for the higher quality areas if possible.
Plant and site characteristics should be considered together in determining the best methods to control weeds. An understanding of ecosystem interrelationships is a prerequisite to altering any one aspect.
A variety of weed control methods are available. Once plant and site characteristics are understood, you can better consider alternatives. Each method will need to be weighed against your work force availability. Methods include controlled burning, mowing, hand cutting, hand pulling, and herbiciding. Use of herbicides poses risks to both people and the environment and should be your last choice.
Controlled burning is a method of weed control that needs to be coordinated with overall site management. Fire has an effect on all other life at the site, including plants, birds, insects, mammals, and herpetofauna. It can promote seed germination of certain species, like white sweet clover. This will not only aid in forecasting when you will encounter future weed control problems, but will also reduce the seed bank for future management. Fire can also be used to control some species. For example, annual burning for 5-6 years controls reed canary grass if native species are reintroduced to compete with it.6
Mowing is another method of weed control that can be very effective under the right circumstances. It is one of the most labor efficient methods available for monoculture areas that are mower accessible. Because the visual appearance of the area would be altered, public reaction should be taken into consideration when considering this method.
Hand cutting can take several forms. Loppers can be used for thick stemmed weeds such as tall goldenrod, whereas clippers work well on removing seed heads (e.g., teasel). Scythes and motorized brushcutters are efficient for removing larger stands of foliage. Each version of hand cutting requires a sufficient work force.
Hand pulling is the most labor intensive weed control method currently in use. If the weed population is dense and extensive, this may not be the best alternative. Soil disturbance as a result of pulling may encourage other aliens to invade after your work force has passed through. Tamping down the soil and/or reseeding will minimize this after-effect.
The use of herbicides should be examined when there are no other reasonable methods available. The first step is to determine what restrictions apply to the site. Forest preserve districts may specify chemicals to be used, whereas the Illinois Nature Preserves Commission may have different guidelines. Private land owners may not allow herbicides, or may allow whatever is on the market for the existing problem.
Several different types of herbicides are on the market. Selective herbicides control only certain plants. For instance, Garlon 3A is a selective herbicide that controls broadleaf plants, with a lesser effect on grasses. Broadleaf herbicides are preferable for conditions where the herbaceous mix has both native grasses and broadleaf weeds.
Non-selective herbicides, such as Roundup, will kill any plants that they come in contact with. This type would normally be considered for the control of grasses (e.g., reed canary grass) or in areas where some drift would not cause regrettable damage.
Wetlands have safety needs specific to themselves. Herbicides have been designed to meet those needs. Rodeo is an example of an aquatic herbicide.
Once an herbicide type is selected, then the application parameters on the label should be carefully examined and strictly observed. Even if all other factors suggest the use of herbicide, these parameters may prevent its use. For example, temperature restrictions with upper and lower limits are specified. All herbicides have precipitation guidelines for current and near future conditions. Roundup, for example, should not be used within six hours of expected (or suspected) precipitation. If the humidity is too high, then runoff of the applied spray will result. If humidity is too low, then the evaporation rate will decrease its effectiveness. If the application day is too windy, then spray drift or vapor drift will occur.
The manufacturer's application parameters are listed on the labels and in the booklets that accompany every container of herbicide sold. This information should be used along with knowledge of plant and site characteristics in determining the proper control method.
Safety is the most important aspect of herbicide use. This includes safety for humans and for the environment. The decision to apply herbicides requires the full responsibility of the applicator to use it in the safest and most effective manner possible. State licenses are required for the applicators and additional safety classes are highly recommended. The subject of safety is broad and will not be dealt with here.
Once you have decided to use herbicide, and an herbicide has been selected, attention should be given to preparation for use. Most herbicides come in a concentrated form, and their labels and instruction booklets recommend various dilutions for control of various species. The herbicides should be mixed either with water or oil and an emulsifying agent, as per the instructions. Whatever medium is used, it should be clean to avoid clogging the nozzles of the application equipment.
In some circumstances, application will be enhanced through the use of a surfactant. Surfactants are liquids that increase the surface tension of the mixture. Increased surface tension decreases drift while spraying, reducing the likelihood of inadvertently killing neighboring plants. They also decrease runoff by helping the mixture remain on the plant surface. This increases intake by the plant, thereby increasing the effectiveness of the herbicide.
Dyes are another useful additive. They help the operator observe where he has sprayed. This increases uniformity of application and safety by making avoidance of sprayed areas easier.
Ingredients should be mixed in a bucket. A filter funnel should be used to avoid spillage and to keep the mixture clean. A measuring cup with ounce increments is useful for proper measurement of ingredients. The mixing rod should be nonporous for easy clean up. A wooden stick is not recommended due to particle contamination of the mixture and disposal problems.
When mixing the ingredients water should be added first, followed in turn by the herbicide, the dye, and the surfactant. This order insures proper mixing of the water and herbicide. The exact proportions should be calculated before mixing begins to avoid confusion and errors. Only the amount anticipated for immediate use should be mixed. Once the mixture is prepared, it should be poured into backpack sprayers, spray bottles or other application devices.
On site, the group leader should provide applicators with proper instructions prior to each session. Safety should be stressed. Plants to be herbicided should be identified in sufficient detail to avoid confusion with other similar species. Herbicide has no conscience and will eradicate the wrong plant as easily as the target species.
Application techniques should also be reviewed prior to each work session. The basic premise is to avoid drift and run-off as much as possible. To do this, all nozzle settings should be set (and readjusted periodically as necessary) to produce a uniform spray pattern without misting. The applicators should spray as close to each plant as possible to avoid drift. Applicators should be given frequent breaks to insure their careful attention.
Herbicides can be an effective means of weed control. However, they should only be used after an exhaustive consideration of the weed's characteristics, site characteristics, alternative control methods, workforce size, landowner requirements, herbicide types and weather conditions. Vegetative management is constantly being researched and tested for new methods of control. Hopefully, in the future, safer and more effective techniques will be available.