1. Soil Tree Herbicide Application
This form of timber stand improvement (TSI) uses soil herbicide uptake by a tree's root system to do the job. It demands an area where mechanical equipment can transport and spray or broadcast the chemical effectively such as under lower basal area stands of mature timber or over newly cleared tracts that are heavily populated with a poor tree species.
Only soil active herbicides (imazapyr, hexazinone, tebithiuron) can be used for this type of application. Since this method is subject to rain runoff, surrounding bodies of water and off-site areas should be taken into consideration. Follow label instructions and check state regulations that apply when using the herbicide.
2. Foliar Tree Herbicide Application
This form of timber stand improvement uses a spray herbicide applied to saturate a tree's canopy and leaves. It also needs an area where mechanical equipment can transport and spray the chemical effectively but can also be done using a backpack sprayer (which can be labor intensive). Complete coverage of the foliage is critical for success but is a great treatment when patches of smaller trees and shrubs are the target species.
Auxin-type herbicides (like triclopyr) are generally most effective early in the growing season as leaves are first appearing. Enzyme-inhibiting herbicides (like imazapyr) are most effective during late summer or fall. Using the ever-popular Roundup (or less expensive generic forms of glyphosate) is most effective in late summer or fall but just before change in leaf color.
3. Bark Tree Herbicide Application
Unfortunately, every individual tree target has to be visited and the entire bark surface sprayed to at least one foot up the tree's base. This can be labor intensive where stem counts are high and is usually only done using a backpack sprayer. Basal applications can be made any time of the year, but are most effective during the dormant season when leaves are not present.
Basal applications will not provide rapid control. Herbicide injury is often not observed for several weeks after treatment and total control may require several months. Additionally, basal treatment is not effective on older trees with thick bark. For older trees, other application techniques should be employed.
Pathfinder is a "ready to use" product (basically triclopyr) that can be used at 100 percent strength. Other generic products are used with a basal oil to include imazapyr. This treatment is most effective on trees with smooth bark and thick bark trees may require retreatment.
4. Stump Tree Herbicide Application
Adding a dye to the herbicide formulation improves application success by showing exact stump coverage. Small stumps should be completely saturated. Stumps greater than 3 inches in diameter can be limited to the outer edge to limit chemical waste and runoff. Remember, the cambial layer around the outer edge is where the action is taking place.
Herbicides using this method can be applied using a backpack sprayer, squirt bottle, or paint brush. Again, no matter how the herbicide is applied, a tracer dye should be included to ensure treatment of all individual stumps. Most of the basic woody-stemmed herbicides can be used including triclopyr, imazapyr and glyphosate.
5. Hack and Squirt Tree Herbicide Application
Apply herbicides I mentioned (under stump cut) in dilution ratios from one-half to one-quarter strength. Read the product label to determine the appropriate dilution. Roundup (glyphosate) undiluted or half-strength is excellent for hack and squirt applications.