glyphosate (Rodeo, Roundup Custom and others)
Rate 50% product concentration v/v in water for stem and stump treatments. For stem treatments make at least one cut per inch of tree diameter with an ax or similar tool and apply one ml of solution per cut. For stump treatment apply a narrow band of solution completely around the cambium just inside the bark.
Time Best results for stem treatments occur from mid-summer through early winter. Late winter and spring give more variable results. Stump treatments should be done right after the tree or stem is cut off regardless of season.
Remarks Glyphosate can control a wide variety of shrub or trees species. Sensitive hardwoods for stem treatment include alder, oaks, and madrone. Conifers can also be treated with at least top kill expected. While labor intensive, many shrubs can be also be controlled by treating each stem. Many deciduous hardwoods and shrubs can also be controlled with a cut stump application. Bigleaf maple will only be suppressed with glyphosate and generally recover.
There are many glyphosate products labeled for forestry use. Users should carefully read the product label they are using and make sure they do not exceed maximum labeled concentrations. Many product labels allow for use of undiluted product for hack and squirt and stump treatment. While effective, dilute solutions appear to work just as well.
Caution Non-target plants of the same species growing near treated plants can possibly be injured through herbicide movement through root grafts.
Site of action Group 9: inhibits EPSP synthase
Chemical family None generally accepted
imazapyr 4 lb ai/gal (Arsenal Applicators Concentrate, Polaris AC Complete, Imazapyr 4 SL and others)
Rate 50% product concentration v/v in water for hack and squirt or stem injection. For stem treatments make at least one cut per three inches of tree diameter with an ax or similar tool and apply one ml of solution per cut or until wet. Some product labels allow for undiluted product use; read labels carefully to use this concentration. For stump treatment mix 4 to 6 ounces of herbicide with one gallon of water and apply a narrow band of solution completely around the cambium just inside the bark. Treat immediately after cutting.
Time Best results for stem treatments occur from mid-summer through early winter. Late winter and spring give more variable results. Stump treatments should be done right after the tree or stem is cut off regardless of season.
Remarks Imazapyr controls the widest variety of trees and shrubs with cut stem treatments in the Pacific Northwest. Bigleaf maple and other maples, alder, cherries, oaks, cottonwood, madrone, chinkapin, ash and tanoak are sensitive. Recovering bigleaf maple sprout clumps are effectively controlled by treating the largest 25-50 percent of the sprouts evenly distributed throughout the clump.
Caution Imazapyr has significant soil activity and readily spreads through root systems. Injury to non-target plants that have root systems connected by root grafts to the same treated species can occur. Conifers growing near treated plants can pick up herbicide residues through root uptake in the soil and exhibit injury symptoms but typically recover. Users should avoid over-application into cuts and stump surfaces that results in stem flow.
Site of action Group 2: acetolactate synthase (ALS) inhibitor
Chemical family Imidazolinone
triclopyr salts (Garlon 3A, Vastlan, Triclopyr 3 and others)
Rate 50% product concentration v/v in water for stem treatments or use undiluted. For hack and squirt make approximately one cut per inch of tree diameter so that cut edges slightly overlap around the circumference and apply one ml of diluted solution per cut. For undiluted product use ½ ml per cut. For stem injection make one cut every 3 to 4 inches on center around the tree. For stump treatment apply a narrow band of undiluted product completely around the exposed cambium just inside the bark after cutting.
Time Best results occur during the growing season. Treatments during late winter and spring sap flow will give more variable results.
Remarks Triclopyr controls a variety of deciduous and evergreen trees including oaks, alder, cottonwood, and madrone. Maples can be partially controlled. For stumps that have been cut but left untreated for an extended time period, labeled triclopyr ester products can be used undiluted. Treat normally around the cambium as with the salt forms.
Site of action Group 4 synthetic auxin
Chemical family Pyridine