Official website of the New Zealand Farm Forestry Association


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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