There are several approaches to applying herbicides for brush control. They range from very simple hand methods to elaborate mechanical means.

Hack And Squirt

Hack and squirt or frill treatment (Figure 1) is a simple method of killing trees with herbicides.

Figure 1. Make a series of downward cuts, leaving the chip, and immediately apply herbicide into cuts.

It is best suited to trees at least 4 to 5 inches in diameter. Bark on larger trees is often too thick for most water soluble sprays to penetrate, so it is necessary to provide a direct pathway for herbicide entry into the plant's vascular system.

Use a hatchet to make a series of downward cuts in the bark around the entire circumference of the tree trunk. For most species, it takes about one cut for every 2 inches of trunk diameter. Frill cuts are overlapping cuts in the tree bark around the stem. Immediately apply the selected herbicide into the cuts. Avoid application during heavy upward sap flow in the spring, when sap flowing out of the wound will prevent good absorption.

Apply herbicides registered for this purpose undiluted or in dilution ratios from one-half to one-quarter strength. Read the product label to determine the appropriate dilution. Amine formulations of Garlon, Grazon, and 2,4-D are generally more effective than esters. Roundup undiluted or half-strength is excellent for hack and squirt applications.

Stem injection (Figure 2) is similar to hack and squirt treatments.

Figure 2. Use special equipment to make injection applications. Injection cuts do not overlap as cut surface treatments do.

Specialized equipment is used to inject a specific amount into the tree at each injection point. Best results occur when injections are made every 2 to 6 inches around the tree. Trees or brush should be at least 1.5 inches in diameter at chest height.

Stump Spray Treatment

Stump spray treatment (Figure 3) involves cutting down a tree and treating the freshly cut surface with a herbicide.

Figure 3. Apply herbicide to the cut stump.

Leave a tree stump 8 to 12 inches above the ground and cut the top of the stump level to allow uniform herbicide coverage. Thoroughly wet the cambium layer next to the bark so the conducting tissue carries the herbicide to the roots.

On larger trees, treat only the outer 2 to 3 inches of the stump. The internal heartwood of the tree is already dead. On trees 3 inches or less in diameter, treat the entire cut surface.
Apply treatment immediately after cutting for maximum effectiveness. While there is some reduction in effectiveness after one hour, it may take about 4 hours before any serious drop-off in penetration occurs. If application is delayed after cutting, recut the stump and apply the herbicide to the live tissue. Delaying herbicide application to freshly cut trees can result in prolific sprouting from the tree collar and roots.

Moisture stress may affect control during the summer and early fall. Applications during the spring upward sap flow are not as successful as late spring and early summer treatments. Pathfinder, Garlon 4, Remedy, and Crossbow are good stump treatment products that mix readily with petroleum based penetrants.

Basal Bark Treatment

Basal bark treatment (Figure 4) involves the application of a herbicide to the lower 12 to 18 inches of the trunk or stem from early spring to mid-fall. Some species can be treated during the winter.

Figure 4. When treating basal bark, apply herbicide to the lower 12 to 18 inches of the tree trunk.

The selected herbicide is mixed with diesel fuel, kerosene, or other suitable carrier and applied until the bark is saturated. The low volatile ester formulations are the only oil soluble products registered for this use. This method is effective on trees of all sizes, but is most commonly used on small brush.

A thinline application (Figure 5) is similar to a basal bark treatment.

Figure 5. Spray a thin stream of herbicide in a narrow band.

A thin stream of undiluted herbicide is sprayed horizontally, to all sides of a lower plant stem, to form a narrow band around each stem or clump. Specialized equipment calibrated to deliver small amounts of herbicide is needed to make such an application.

Foliage Treatment

Foliar treatment (Figure 6) is a common method of treating brush up to 15 feet tall by hand.

Figure 6. Use foliage treatments for brush up to 15 feet tall. Treatments are least effective during very hot weather or when trees are water stressed.

Timing varies from early summer to late September, depending on the herbicide used. Foliar treatments are least effective during very hot weather and when trees are under drought stress.

Herbicides such as 2,4-D, Banvel, Garlon, and Grazon can be applied in the early summer, while the herbicide Accord provides best results when applied in August or September. Arsenal applied from June through September provides best results.

Adding a surfactant improves the performance of most foliar applied herbicides. Drift control additives are also available to reduce the number of fine droplets produced. DO NOT use diesel fuel as an additive when applying herbicides to foliage. Diesel fuel kills the leaves before the herbicide can be translocated by the plant. Spraying until runoff is not necessary. Spray to wet the leaves and keep moving.

Soil Treatment

Herbicides applied to the soil surface (Figure 7) move into the root zone of the target plants with rainfall.

Figure 7. Apply herbicides evenly to the soil above the root zone in soil treatments. Rainfall carries the herbicide into the root zone.

Commonly used soil-applied herbicides include Spike and Hyvar. Spike may be applied in narrow bands. Banding, also called braiding or lacing, involves the application of a concentrated herbicide solution to the soil in a line or narrow band spaced every 4 to 6 feet. This type of application is used to kill large numbers of trees as in the case of a fence row. Soil active herbicides may also be applied on a spot or individual tree basis with an exact delivery handgun applicator, known as a spotgun.