Application Methods for Herbicides

Herbicides can be applied in a variety of ways. The most appropriate application method is determined by assessing the species being treated, the herbicide being applied, the skills of the applicator and the conditions at the application site. Standard application techniques can sometimes be modified to effectively meet natural resource and invasive plant management goals.
Site Selection
Site conditions also should be considered before choosing an application method. Consider accessibility, proximity to open water, depth to groundwater, the presence of rare species and other conservation targets, and the site's sensitivity to trampling that could occur when the herbicide is being applied.
Record Retention
When using herbicides, it is critical (and, in some cases, required by law) to keep records of all the species and sites that are treated, the amounts and types of herbicide used and the dates of application. This information will be important in evaluating the project's success, improving methodology and identifying mistakes. In addition, it documents the procedure for future site managers and biologists. Records of abundance/condition of the targeted invasive plants and nearby desirable plants before and after treatment will also be valuable in evaluating the effectiveness of the herbicide.
foliar spray_art goverFoliar Applications
These methods apply herbicide directly to the leaves and stems of a plant. An adjuvant or surfactant is often needed to enable the herbicide to penetrate the plant cuticle - a thick, waxy layer present on leaves and stems of most plants. Foliar application methods can range from very specific spot treatments through spray or wick equipment or more general broadcast spraying with hoses or boom applicators attached to a tractor or other motorized equipment. Spot applications are preferred when possible to ensure non-target specimens are not treated with herbicides and to cut back on the amount of chemical applied.
A.    Spot applicators - Spray herbicide directly onto target plants only, and avoid spraying other desirable plants. These applicators range from motorized rigs with spray hoses to backpack sprayers, to hand-pumped spray or squirt bottles.  
B.    Wick (wipe-on) applicators - Use a sponge or wick on a long handle to wipe herbicide onto foliage and stems. Use of a wick eliminates the possibility of spray drift or droplets falling on non-target plants. However, herbicide can drip or dribble from some wicks.
1.     "Paint sticks" and "stain sticks" sold at local hardware stores have been used successfully for wick application. These sticks have a reservoir in the handle that can hold herbicide, which soaks a roller brush at the end of the handle. The brush is wiped or rolled across leaves and stems.
2.     The "glove of death" is a technique for applying herbicide in an otherwise high quality site. Herbicide is sprayed directly onto a heavy cotton glove worn over a thick rubber/latex (or nitrile) glove. The wearer of the glove can then apply the herbicide with total precision and little or no runoff.  
C.    Boom applicator - A boom, a long horizontal tube with multiple spray heads, is mounted or attached to a tractor, ATV (or other four-wheel drive vehicle), helicopter, or small plane. The boom is then carried above the weeds while spraying herbicide, allowing large areas to be treated rapidly with each sweep of the boom. Offsite movement due to vaporization or drift and possible treatment of non-target plants can be of concern when using this method. 
Basal Bark
This method applies a six to 12 inch band of herbicide around the circumference of the trunk of the target plant, approximately one foot above ground. The width of the sprayed band depends on the size of the plant and the species' susceptibility to the herbicide. The herbicide can be applied with a backpack sprayer, hand-held bottle or a wick. Ester formulations are usually best for basal bark treatments, as esters pass through the bark more readily than salts. Esters can be highly volatile, however, so basal bark treatments should be performed only on calm, cool days. During summer, treatment is best carried out in the mornings, which tend to be cooler. The basal bark treatment works best on young trees with smooth bark. It is usually not effective against older plants with thick corky bark.
hacknsquirt_james miller_usda fsHack and Squirt
The hack and squirt method is often used to treat woody species with large, thick trunks and bark. The tree is hacked with a small ax or hatchet, or drilled with a power drill or other device. Herbicide is then immediately applied to the exposed wood with a backpack sprayer, squirt bottle, syringe or similar equipment. Because the herbicide is placed directly onto the thin layer of growing tissue in the trunk (the cambium), an ester formulation is not required.
Herbicide pellets can be injected into the trunk of a tree using a specialized tool such as the EZ-Ject Lance©. The lance's five-foot-long, metal tube has "teeth" on one end that grip the trunk of the tree. A sharp push on the other end of the tube sends a brass capsule of herbicide into the tree trunk. It is a convenient way of applying herbicide and requires minimal preparation, little exposure to the chemical and easy clean up.

However, there are some serious drawbacks to this method. The lance and capsules are expensive and full-sized lances can be unwieldy, particularly in thickets. The lance is difficult to thrust with enough power to drive the capsules far enough into thick barked trees to be effective. A large number of capsules placed close together are often necessary to kill large trees.
cut stump_james miller_usdafs_forestryimagesCut-Stump
This method is often used on woody species that normally re-sprout after being cut. The tree or shrub is cut, and herbicide is immediately applied to the exposed cambium (living inner bark) of the stump. The herbicide must be applied to the entire inner bark (cambium) within minutes after the trunk is cut. The outer bark and heartwood do not need to be treated since these tissues are not alive, although they support and protect the tree's living tissues.

Herbicide can be applied to cut stumps in many ways, including spray and squirt bottles, or even paint brushes. Care must be taken to avoid applying too much herbicide, causing the chemical to run-off the stump and onto the ground. Herbicide can also dribble from bottles or brushes, potentially falling onto non-target plants or the ground.
Sometimes even treated stumps will re-sprout, so it is important to check regularly (two to six months) for at least a year. Depending on the vigor of the re-sprouts, these can be treated by cutting, basal bark applications or foliar applications. Even when foliar applications are a necessary follow-up treatment, applying herbicide to the re-sprouts is usually easy and requires minimal chemical use.
The cut stump treatment allows for a great deal of targeted control of invasive plants with a low probability of affecting non-target species or contaminating the environment. It also requires only a small amount of herbicide to be effective.