1/3/2011
2010 Project Report for
Oregon Nursery Research Regulatory Committee of ODA
Testing Plant Health Evaluation Tools
Submitted By:
Chal Landgren, OSU Christmas tree Specialist, North Willamette Research and
Extension Center, Aurora OR. 97002. Phone 503. 678-1264 Ext. 114 FAX 503.
678-5986
E-mail chal.landgren@oregonstate.edu
Project Assistance Provided by:
Mike Kapsimalis, NWREC Nursery Intern- Field Data Collection and Testing
Dr. Jim Owen, Nursery Specialist- Data Analysis
Judy Kowalski, Nursery Technician- Plant Monitoring
Dr. Ryan Contreras, Assistant Professor- Chlorophyll Testing
Project Background and Review
There are a number of plant evaluation tools for field crops and shade trees used
to gauge plant health, nutrient status or color. Devices such as SPAD, Ping,
BRIX meters, various goggles (infrared), digital imaging techniques like NDVI etc.
are currently used with varying degrees of success on other crops. Few of these
have been used on conifers.
Thanks to an OAN/ODA grant in 2009, we had conifer plant material (Nordmann
fir and Blue Spruce) with known past histories and documented levels of foliar
nutrients and growth. These are located at NWREC and provide excellent test
cases to evaluate these tools. In addition, a number of field sites provide access
to plants with known nutrition levels.
Materials and Methods
Our first task was an evaluation of the types of “tools” to use in the more detailed
plant analysis. The tools we considered for conifer analysis were the following:



CM 1000 Chlorophyll Meter
PING and SPAD Meters
Digital hand-held Refractometers (Brix type Meters)



GreenSeeker (NDVI)
Various color charts
Plant Stress Detection Glasses
These “hand held” field tools would then be used in reference to laboratory
evaluations of plant tissue testing, Chlorophyll monitoring and visual/physical
assessments.
The first challenge was determining which tools could be used with or adapted to
evaluation of conifer needles; in our case, Nordmann fir and Blue Spruce.
Needles, unlike leaf surfaces, are rather opaque, waxy, round and narrow. Given
that a number of the devices require either penetrating light or a restriction of
ambient light interference, the PING and SPAD meters were deemed
inappropriate for conifer use and abandoned.
The CM 1000 Chlorophyll type meters are dependent on ambient light reflection
and thus time of day and sun angle influence the readings. This limitation
suggested that inconsistent readings would further limit use on conifers.
The GreenSeeker device is an active sensor emitting light at 2 specific
wavelengths and measuring the light reflected from the target and then
calculating a Normalized Difference Vegetation Index (NDVI) based on a ratio
between the two wavelengths. The device has been used successfully in
measuring the N status of grass seed trials and other in crops. With the active
sensor, we hoped that time of day, sun intensity and other variables would show
minimal variation. We continued then with further evaluations using the
GreenSeeker.
Digital hand-held Refractometers (Brix type Meters) are commonly used to
evaluate sugar content of fruit. There are a few Christmas tree growers
advocating their use in conifers. We selected this tool for further evaluation.
Color charts and Plant Stress Detection Glasses were also selected for additional
evaluation as they are simple and easily used.
To summarize, we selected the following tools for further testing 



GreenSeeker
Digital hand-held Refractometers (Brix type Meters)
Color Charts
Plant Stress Detection Glasses
In the evaluation of these devices, we used containerized Nordmann fir and Blue
Spruce grown in unheated greenhouses at the North Willamette Research and
Extension Center. These trees had a known fertilization history (soil and foliar)
and each individual plant has known foliar nutrient contents, measured growth
and development values and on selected individuals, measured needle
Chlorophyll and Carotenoid Content (averaged from 3 sample levels on each
tree).
The tools were also evaluated at 2 field sites with known fertilization histories.
GreenSeeker Evaluation Methods
This tool is traditionally used above the crops canopy with the laser pointed
towards the ground; we had to adapt the tool for use on conifers. With the wide
range of plant heights we found it impractical to hold the laser above a tree,
which in field production is usually between 5’-12’. Next, we decided to hold the
device parallel to the side of the tree and take readings. Our concern however,
was whether or not the laser would be disrupted by the suns influence or the
space between trees. One study (Kim, 2010) suggested that there was no
significant effect observed within 0-60 degree zenith angle as indicated by the
limited variation in NDVI responses. With this information, we decided it would be
accurate to hold the GreenSeeker on a side angle and measure a 2’ swath with
the sensor head 2’ away from tree.
This worked, but we found wildly varying reading using the device in a hand-held
manner. In other words, we found that the sensor head angle and distance to
the plant surface remained a critical variable, especially on younger and open
grown trees. To compensate, we mounted the GreenSeeker to a fixed wagon
platform so that the laser would be two feet from the tree canopy and measure
from the base of the lowest branches and two feet above. Using the wagon gave
much more replicable data. In dense field grown situations on larger trees this
variable was less noticeable.
Digital hand-held Refractometers (Brix Meters) Evaluations
A local Christmas tree grower has developed a theory that low Brix readings
(<12) suggests trees are more susceptible to pest problems while higher Brix
readings means insects such as aphids can not process complex sugars and
thus less likely to have insect infestations. We visited with this grower to observe
his evaluation methods and eventually fabricated our own device to extract liquid
from needles for Brix testing.
Color Charts
Past evaluations of fertilizer responses in conifers resulted in comparing a
number of color evaluation “systems” such as Munsell, Royal Horticulture Society
Color Fans and various paint store color chips. From these we determined that
the range of needle colors in most conifers are best represented and matched
with the Royal Horticulture Color Fan System. This system also is one of the few
that is supported by a computer graphing and evaluation process.
Plant Stress Detection Glasses
We purchased a pair of these purple glasses (designed by NASA, the ad said) to
see if they offered any evaluation assistance. In testing we simply put the glasses
on and observed the same trees with and without the glasses to evaluate any
“added value”.
Results
GreenSeeker:
Once a system was developed to stabilize the sensor head, we were able to
obtain consistent measurements with repeated evaluations.
As tables 2 and 3 illustrate, the range of NDVI readings varied widely between
trees with the same fertilization treatments. Nor were the readings suggestive of
foliar N levels, plant color, vigor or Chlorophyll/Carotenoids as illustrated best in
table 3. In short, the NDVI readings showed variation, but were not related to any
consistent standard of plant health.
In summary, NDVI readings on conifers seem to offer little predictive value
relative to foliar N % or Chlorophyll content.
Brix:
After a number of broken plant presses needed to extract liquid from needles, we
developed a prototype model that worked quite well. Yet we found with continued
evaluations that we were getting very different readings from drops and the
beginning of pressing compared to the end. The first few drops showed lower
readings, the middle drops were a little higher, and the last drops to come out
were very thick and usually had a high Brix reading. To compensate, we
developed a process for mixing the samples. This provided more consistent
results. However on further evaluation we found large daily variation in Brix
readings taken from the same trees (table 1). In another trial, we compared Brix
readings from aphid infested trees and trees without aphids. No difference were
noted.
Table 1. Brix values over 8 hours
DF needles
AM
AM
AM
PM
PM
PM
9.6
13.5
17.2
10.2
8.4
16.5
In summary, Brix measures on conifers were of little diagnostic value, varied
widely during the day, from tree to tree and not correlated to plant health.
Color Rating
In contrast with NDVI and Brix measurements, color rating closely matched plant
Chlorophyll and N%. Briefly, the darker the green hue, the higher the Chlorophyll
value and N%
Plant Stress Detection Glasses
The glasses provided a somewhat disorienting view due to the off-color view of
the plant. They were unable to distinguish foliar N levels or Chlorophyll. However,
we found them quite good at detecting necrotic needles from healthy needles, so
were useful in detecting Current Season Needle Necrosis, dying branches and
so on.
Conclusions
Many of the plant health evaluation devices that have been developed for and
used on grasses or leafy plants appear unsuited to conifers. The most
immediately promising device that we investigated was the GreenSeeker. After
many months of field usage and a number of modifications, the device does not
appear to provide readings that correlate with tissue N, plant Chlorophyll or
apparent plant vigor/color.
Likewise, Brix readings on Nordmann fir, Douglas-fir and noble fir are highly
variable from tree to tree and change through the day. The utility of this measure
as a predictor of tree health or N status is highly dubious.
The human eye and a good color chart (such as the Royal Horticultural Color
fan) are actually excellent tools at evaluating plant vigor and health. The addition
of the stress detection glasses, may assist in detecting dead or necrotic tissue,
but have little utility beyond that.
Table 2. Selected data comparing treatments with Chlorophyll, NDVI, N and color ratings
Nordmann
Fir #
Treat
Rep
Des
1
r
1
CRF-Osmocote+F1
18-5-9
6
r
2
8
r
10
Chloro(mg/g
weight)
dry
Carot (mg/g dry
weight)
NDVI
N%
B (ppm)
RHS rating
x
y
Y
2.16
0.38
0.83
2.11
9.2
147A
0.33
0.4
8.1
CRF-Osmocote+F1
18-5-9
1.85
0.32
0.76
2.09
15.3
147A
0.25
0.28
42.3
3
CRF-Osmocote+F1
18-5-9
2.40
0.40
0.64
2.23
9.8
147A
0.33
0.4
8.1
b
1
CRF-Osmocote 18-5-9
2.00
0.34
0.56
2.2
5.1
147A
0.33
0.4
8.1
13
b
2
CRF-Osmocote 18-5-9
1.51
0.26
0.73
1.73
5.3
137B
0.327
0.414
12.6
16
b
3
CRF-Osmocote 18-5-9
2.40
0.37
0.79
2.09
4.9
147A
0.33
0.4
8.1
19
w
1
Untreated Control
0.69
0.14
0.69
0.86
4.5
146A
0.335
0.349
53.5
20
w
2
Untreated Control
0.67
0.15
0.79
0.82
4.5
144A
0.382
0.501
20.9
22
w
3
Untreated Control
0.72
0.16
0.78
1
5
146B
0.363
0.436
18.2
25
g
1
Foliar/All Helena (F1)
w/exclusion
1.19
0.21
0.81
0.84
7.6
144A
0.382
0.501
20.9
26
g
2
Foliar/All Helena (F1)
w/exclusion
0.51
0.12
0.84
0.9
7
146A
0.366
0.447
11.8
31
g
3
Foliar/All Helena (F1)
w/exclusion
0.36
0.09
0.71
0.67
13.3
153A
0.429
0.48
35.4
33
y
1
Foliar/Wilbur-Ellis 138-8
0.74
0.15
0.70
1.14
6.1
146A
0.366
0.447
11.8
35
y
2
Foliar/Wilbur-Ellis 138-8
0.63
0.13
0.54
0.87
4.7
146A
0.366
0.447
11.8
38
y
3
Foliar/Wilbur-Ellis 138-8
0.61
0.12
0.78
0.89
5.7
146B
0.363
0.436
18.2
44
p
1
Foliar/HelenaKayphol,CoBo,PhosC
alZn
0.61
0.13
0.69
0.77
16.4
144A
0.382
0.501
20.9
45
p
2
Foliar/HelenaKayphol,CoBo,PhosC
alZn
0.64
0.17
0.83
0.72
8.1
151A
0.411
0.476
42.5
46
p
3
Foliar/HelenaKayphol,CoBo,PhosC
alZn
0.453420
0.103905
0.774
0.74
15.3
144A
0.382
0.501
20.9
Treat = Tag Color ID
Des = Description of treatment
Chloro = Chlorophyll Content (mg/g dry tissue weight)
Carot = Carotenoid Content (mg/g dry tissue weight)
RHS rating = Royal Hort. Science Color Chart
x, y, Y = C.I.E. co-ordinates
Table 3. Summary of Average Values for Nordmann fir at NWREC by treatment
(see table above for row label treatments.)
Row
Labels
b
g
p
r
w
y
Values
Average of
Chloro (mg/g dry
weight)
1.97
0.69
0.57
2.13
0.70
0.66
Average of
Carot (mg/g
dry weight)
0.32
0.14
0.13
0.37
0.15
0.14
Average
of NDVI
0.69
0.79
0.77
0.74
0.75
0.67
Average
of N %
2.01
0.80
0.74
2.14
0.89
0.97
Average of
B (ppm)
5.10
9.30
13.27
11.43
4.67
5.50
References
Kim, Y, D.M. Glenn, J. Park, H.K. Ngugi, B.L. Lehman. 2010. Active Spectral
Sensor Evaluation under Varying Conditions. 2010 ASABE Meeting
Presentation. Paper #1009111.
Cregg, B., et. al. 2004. Chlorophyll Florescense and needle chlorophyll
concentration of fir (abies sp) seedlings in response to pH. Hort Sciencr 39(5)
pgs 1121-1125
Murdock, L. Call, D. Janems, J. 2004 Comparison and use of chlorophyll meters
on wheat (reflectance vs transmittance/absorbance AGR-181 Univ. of Kentycky
Cooperative Extension Service