General herbicide treatment advice
Treatment timing is vitally important to herbicide success. In almost all cases, herbicides should be
applied only when the plants are in full leaf (annual plants can often be effectively treated earlier).
Results are generally poor if the plants are sprayed prior to this stage. Although some literature
suggests the best results on deep-rooted perennials occur when plants are sprayed at flower bud stage,
after flowering or even seed-set, local experiments suggest that the ideal treatment timing depends on
the specific treatment being undertaken and the chemical chosen. For HBB it is best to spray in late
summer or fall, especially if glyphosate is being used. The effectiveness of all foliar applied herbi-
cides will be reduced significantly if the plants are badly moisture-stressed.
With all herbicides, complete coverage of all canes and leaves, including those growing from suckers
away from the main bush, is essential for maximum effectiveness. Use of appropriate adjuvants
(additives including surfactants, penetrants, sticker-spreaders, etc.) can greatly enhance herbicide
effectiveness. Regrowth of HBB after slashing, burning, or grazing should be at least 18 inches (500
mm) high before herbicide application. Finally, more is not better. For effective control of deep-
rooted perennials it is often better to keep the herbicide rate low, so above ground plant tissue does
not die before the herbicide can be translocated deep into the root system.
In applying herbicides it is recommended that a dye be used in the chemical mixture to mark the
treated plants and thus minimize waste.
Review of published literature and local knowledge on herbicide treatment choices for broad-
cast application (A more detailed and well-referenced review is available on TNC’s wildland weed
website: tncweeds.ucdavis.edu)
Many herbicides have been used in an attempt to control HBB with varying degrees of effectiveness.
Picloram (Tordon) is effective, but one application may not always be sufficient. Although Picloram
suppresses cane regrowth, it stimulates the development of adventitious shoots. Foliage spraying is
more effective in the summer than winter.
Fosamine is not as effective as Picloram at killing mature HBB, but is more effective in controlling
regrowth. Neither Fosamine nor glyphosate provide long-term control of HBB (Editors note: results
with glyphosate appear to be greatly influenced by treatment timing). HBB control has also been
accomplished with Dicamba, Imazapyr, triclopyr ester and amine and 2,4-D. Crossbow (a 2,4-D -
triclopyr ester combination) has widespread renown as a blackberry killer. Triclopyr amine alone is
found in many products labeled for control of blackberry and other perennial plant species and has
proven effective in local trials conducted by the City of Portland.
The Multnomah Soil and Water Conservation District reports success using Roundup (glyphosate
with a trademarked surfactant by Monsanto) at standard label rates in a fall application. They did not
find earlier treatment timings to be effective. Representatives from Monsanto recommend a 2:1 tank
mix of glyphosate (Round-up) with triclopyr (Garlon 3a), with Round-up rates at 2% or less and
Garlon 3a rates at 1% or less. Be sure to add most of the water to your tank mix of glyphosate before
adding the Garlon 3a to avoid incompatibility problems.