NZ Farm Forestry - Research trial: Late chemical thinning of cypress and Douglas fir on alluvial soils

Research trial: Late chemical thinning of cypress and Douglas fir on alluvial soils

By Dean Satchell, Claire and Terry Gavin , January 2020.

Chemical thinning of trees has some advantages over manual felling. There is less work and time involved, none of the dangers of manual felling operations and the trees die slowly and cause less disturbance to the canopy, and therefore less risk of windthrow. In addition, the felled trees do not get in the way of the operator undertaking the thinning operation, adding to the cost-efficiency improvement.

The risk with chemical thinning is that unintended injury or death of residual crop tress can occur if the dose used to kill adjacent trees is too high. Trees root-graft and roots can carry translocatable herbicides from one tree to another.

This reseach provides dosing information to foresters who wish to thin their production stands using glyphosate to poison target trees.

FURTHUR POISONING IN DOUGLAS FIR, MAY 2019.

Claire and Terry Gavin.
We did a further poisoning programme on all our doug firs. Poisoning was done at the start of winter in first week of May 2019 with the strongest dose of glyphosate i.e. 1 part of Roundup 510g/l with 2 parts water i.e.1 in 3 dilution (dilution A in the trial). Again 3 ml per hole spaced each hand span around the circumference of the trunk.

Trees were checked June, July, and August 2019…no sign of any yellowing of needles. We initially thought that the poison had not worked with the trees shutting down for winter.

Then in the second week in September 2019 with the start of spring we found a green carpet of Doug Fir needles under the poisoned trees.

On checking a sample area of these trees in mid January 2020: 45 trees checked. Of these 41 trees dead, 3 alive, 1 barely alive. The trees still surviving were all larger specimens. Of particular note no adjacent trees showed any signs of damage.

We only had time to observe these 45 trees but we'd expect that a similar result would be replicated in the remaining trees poisoned.

We will look at further Doug fir areas we have poisoned and see if the results are replicated in other areas and also if over time there is progressive mortality.

Methods

Poisoning was carried out on 13/12/2018 at the gavin's tree farm beside the Buller river near Murchison, in the Tasman Region of the South Island. Three different doses of glyphosate were trialed in each of the 3 blocks of trees (Douglas fir, Ovensii, and in Leyland cypress var Ferndown). There are 10 trees for each dilution in each block. i.e. 30 trees for each tree type.

The tree species tested in this experiment are all known to root graft, evidenced by examples where completely girdlesd trees stay alive and stumps from felled trees stay alive and become covered by cambium.

Age of the trees in this trial was 15 years old, at the upper limit of age where thinning still remains viable.

14 mm diameter drill holes at waist to chest height were made in the tree to be poisoned at approximately 10 cm intervals around the circumference of the tree. Holes were drilled with a downward slope and only deep enough to retain the dose in the sapwood (e.g. 3-4cm). The dose for each hole was 3ml of the diluted glyphosate.

Dilution A ---1 part glyphosate 510g/l (Roundup® MAX) with 2ml water (1 in 3)
Dilution B ---1 part glyphosate 510g/l (Roundup® MAX) with 5ml water (1 in 6)
Dilution C —1 part glyphosate 510g/l (Roundup® MAX) with 11 ml water (1 in 12)

Results

Only 2 out of the 96 trees in the trial were still alive two years after poisoning. These two trees were dosed at the weakest dilution and were both Douglas firs. These two trees were among the larger trees in the trial. At all three doses, no deaths of adjacent trees occurred.

Observations by Terry and Claire

We have found that poisoning is relatively easy to do, particularly in the cypress which had been pruned previously. We used a small chainsaw to clear the lower branches of the Douglas fir trees to be poisoned to allow access. Even with doing this the process is very much quicker, easier and less dangerous than thinning by felling.

We found it quite hard to determine tree mortality in the shorter term. Looking up into the canopy it was difficult to determine whether that branch is green or brown? Which tree does that green foliage belong to? However with progressive observations and the passage of time the results became increasingly clear.
Our greatest worry was whether there would be damage to adjacent trees via root grafting. Happily we have seen no non poisoned trees damaged in any of the areas treated.

Ovensii
Poisoning carried out 13/12/2018	First observation 25/1/2019	Second observation 5/3/2019	Third observation 14/04/2019	Final observation 20/1/2020
A1	Brown top and bottom	Dead	Dead	Dead
A2	Brown top, browning below	Dead	Dead	Dead
A3	Brown top, browning below	Dead	Dead	Dead
A4	Brown top, browning below	Dead	Dead	Dead
A5	Brown top, browning below	Dead	Dead	Dead
A6	Nearly dead	Dead	Dead	Dead
A7	Nearly dead	Dead	Dead	Dead
A8	Nearly dead	Dead	Dead	Dead
A9	Nearly dead	Dead	Dead	Dead
A10	Nearly dead	Dead	Dead	Dead

B1	Green, short, no leader	80% green	60% Dead	Dead
B2	Brown top, brown tips below	Tinge of green	Dead	Dead
B3	Brown top, browning below	Dead	Dead	Dead
B4	Brown top, browning below	Dead	Dead	Dead
B5	Brown top, browning below	Dead	Dead	Dead
B6	Brown top, browning below	Dead	Dead	Dead
B7	? top, browning below	Green tinge, double leader	Dead	Dead
B8	Brown top, browning below	Dead	Dead	Dead
B9	Brown top, browning below	Dead	Dead	Dead
B10	Brown top and below	Tinge of green	Dead	Dead

C1	Browning tips above and below	Tinge of green	90% dead	Dead
C2	Brown top, browning below	Dead	Dead	Dead
C3	? top, brown tips below	70% dead	70% dead	Dead
C4	Greenish, some brown	80% dead	90% Dead	Dead
C5	Brown top	80% dead	Dead	Dead
C6	Greenish, some brown tips	Dead	90% Dead	Dead
C7	Brownish tips	Dead	Dead	Dead
C8	Brown top, browning below	80% dead	90% Dead	Dead
C9	? top, browning tips	80% dead	Dead	Dead
C10	Browning	80% dead	80% Dead	Dead
C11	Brown top, browning below	80% dead	90% Dead	Dead
C12	Brown top, browning below	90% dead	Dead	Dead
No collateral damage seen at 2 years after poisoning at any dilution

DOUGLAS FIR
Poisoning carried out 13/12/2018	First observation 25/1/2019	Second observation 5/3/2019	Third observation 14/04/2019	Final observation 20/1/2020
A1	Dead top	Dead	Dead	Dead
A2	Dead top	Dead	95% Dead	Dead
A3	Dead top	Dead	Dead	Dead
A4	Dead top, green below	Dead top, fair amount green	90% Dead	Dead
A5	Dead top, browning below	Dead	Dead	Dead
A6	Dead top, green below	Dead top & tips/ some green	Dead	Dead
A7	Dead top, green below	Dead top & tips/ some green	Dead	Dead
A8	Dead top, green below	Dead top & tips	Dead	Dead
A9	Dead top, green below	Dead	Dead	Dead
A10	Dead top, sparse, green below	Dead	Dead	Dead

B1	Dead top, little green below	Dead	Dead	Dead
B2	? top, sparse green below	Dead top, green below	90% dead	Dead
B3	? top, sparse green below	Dead top, green below	80% dead	Dead
B4	Dead top, little green below	Dead top and tips	90% dead	Dead
B5	Dead top – most foliage green	Dead top, green below	80% dead	Dead
B6	? top, mostly green, double leader	Dead top, green below	Dead	Dead
B7	Dead top, green below	Dead top, little green below	Dead	Dead
B8	Dead top, little green below	Dead top and tips	Dead	Dead
B9	Dead top, green below	Dead top and tips	80% dead	Dead
B10	Dead top, green below	Dead top and tips	Dead	Dead

C1	Green	Dead top and lots of green	80% dead healthy green crown	Alive
C2	Green	Dead top ,some green below	Dead	Dead
C3	Green	Dead top, lots of green	90% dead	Dead
C4	Brown	Dead	Dead	Dead
C5	Green	Dead top, lots of green below	80% dead	Dead
C6	Brown top, green below	Dead top, mainly brown	Dead	Dead
C7	Green top	Dead top, mainly brown below	Dead	Dead
C8	Green top	Dead top, green below	70% dead	Alive
C9	Green top	Dead	Dead	Dead
C10	? top, browning below	Dead top	Dead	Dead
C11	Dead top, small tree , green below	Dead, small tree	Dead	Dead
C12	Green		70% dead	Dead
C13	Slight damage top and below	Dead top, green below	Dead	Dead
No collateral damage seen at 2 years after poisoning at any dilution

LEYLAND CYPRESS (FERNDOWN)
Poisoning carried out 13/12/2018	First observation 25/1/2019	Second observation 5/3/2019	Third observation 14/04/2019	Final observation 20/1/2020
A1	Dead top, browning lower	Dead top, 90% dead	Dead	Dead
A2	Dead top, browning lower	Dead top, 90% dead	Dead	Dead
A3	Dead top, browning lower	Dead top, 90% dead	Dead	Dead
A4	Dead top, browning lower	Dead top, 90% dead	90% dead	Dead
A5	Dead top, browning lower	Dead	95% dead	Dead
A6	Dead top, browning lower	Dead top, 90% dead	Dead	Dead
A7	Dead top, browning lower	Dead top, 90% dead	Dead	Dead
A8	Faint browning only, small tree	80% dead	80% dead	Dead
A9	Dead top, browning lower	Dead	Dead	Dead
A10	Dead top, browning lower	Dead	Dead	Dead

B1	Dead top, browning below	Dead	95% dead	Dead
B2	Browning tips below	Dead	Dead	Dead
B3	Dead top, browning below	Dead	Dead	Dead
B4	Dead top, browning below	Dead top, 80% dead	95% dead	Dead
B5	Dead top, browning below	Dead top, 80% dead	90% dead	Dead
B6	Dead top, browning below	Dead top, 80% dead	80% dead	Dead
B7	Dead top, browning below	Dead top, 80% dead	90% dead	Dead
B8	Dead top, browning below	Dead top, 80% dead	Dead	Dead
B9	Dead top, browning below	Dead	95% dead	Dead
B10	? top, brown tips below	Dead	95% dead	Dead

C1	Green	Dead top 70% dead below	90% dead	Dead
C2	Browning tips high up	Dead top, 60% dead below	80% dead	Dead
C3	? top green, slight brown tips below	Dead top, 80% dead below	80% dead	Dead
C4	Dead top, green below	Green top, 70-80% dead below	80% dead	Dead
C5	Dead top, green below	Dead top 60 % dead below	80% dead	Dead
C6	Dead top, green below	Green top, 60% dead below	80% dead	Dead
C7	Dead top, green below	Dead top, 30% dead	60% dead	Dead
C8	Browning top,, green below	Green top, 70% brown below	80% dead	Dead
C9	Dead top, browning below	Dead top, 70% dead	90% dead	Dead
C10	Dead top, browning below	Dead top, 80% dead	95% dead	Dead
C11	Dead top, browning below	Dead top	80% dead	Dead
No collateral damage seen at 2 years after poisoning at any dilution

One post

Post from Peter Wilks on January 29, 2020 at 9:40AM

Great idea. I suspect we will see more chemical thiining in the future as it is more difficult to get blocks economically manual chainsaw thinned. My only concern is will the dead poisoned trees still standing pose a risk at time of harvesting? With more mechanised felling maybe not?

Peter Wilks

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Research trial: Late chemical thinning of cypress and Douglas fir on alluvial soils

FURTHUR POISONING IN DOUGLAS FIR, MAY 2019.

Methods

Results

Observations by Terry and Claire

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