Application calculation for 2x trunk tree based on diameter


Well-Known Member
When a tree has two trunks emanating from the ground, do you guys think a rate calculation should be based on the cumulative diameter of the trunks, the diameter prorated from the cumulative area of their cross section, the circumference (representing cambium capacity?), the root zone, or some other measure? I'm asking about construction-impacted trees where paclobutrazol will be applied.

If I do it by diameter, it looks like this:

10"+10" = 20"

If I do it by area, it looks like this:

10" diameter -> 78" area, so:

Or like this:
20" diameter -> 314" area

Just seems like I could easily apply too much or too little with that disparity. What parts of the tree biology bear the most on deciding application rate, and what is the label rate for this circumstance where the label rate is calculated according to dbh?


Well-Known Member
What size of tree does the canopy "look like"? If the whole picture makes it look like a 10" tree I would treat it more like a 10" tree. If the two drunks trunks are widely divergent such that it looks like two individual 10" trees I would use a higher rate.
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Most well-known member
Watch out for those divergent drunks for sure.

I think paclo labels address where to measure such trees but I usually use a slightly lower rate than the label says.


Well-Known Member
You could always find the square root of each dbh squared and added together. 12” and a 8” would be 12x12 + 8x8. 144+64=208. Square root of 208 is 14.4”. I usually do that for multistemmed and codominant


Well-Known Member
FYI, copy and paste off of Cambistat label:

Multi-stem Split Below DBH: For a tree that has multiple stems
splitting below DBH, measure the tree at the narrowest point between
the root flare and the split.
Stem Clusters: For trees that are grown too close together to be
treated as individual trees, measure the DBH of each stem and add the
measurements together. You may need to make rate reductions due to
overlapping canopies (see Dosage Reduction Considerations). Also,
because of close proximity of trees, it may be necessary to apply
Cambistat to outer perimeter of clumped trees.
Tree Splits at DBH: For a tree that splits into two or more stems at
DBH, measure and add the diameter of the stems and measure the
narrowest point below the split. Take the average of theses values.

Canopy Missing: Look at the canopy of the tree and compare it to a
“normal” canopy for that trunk diameter. For example, if a tree is
missing large branches from storm damage or utility line clearance
pruning it is necessary to estimate the percentage of canopy missing and
subtract this percentage from the dosage amount. i.e. subtract 30%
from dosage if 30% is missing from the canopy.
Canopy Suppression: Trees growing in close proximity to other trees,
multi-stemmed trees, and trees growing in clusters may have overlapping
canopies. Your judgment is required to compare the canopies of these
trees to the “normal” canopy for trees with similar trunk diameter. It may
be necessary to reduce the dosage amount based on the percent of
suppression and canopy overlap
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