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Volume 3, Number 13 February 2014
Alert
Licorice Plant (Helichrysum):
Disorder Diagnostics
-
tion photographs of the major disorders associated
with the licorice plant (Helichrysum petiolare).
by Brian E. Whipker1
(bwhipker@ncsu.edu),
W. Garrett Owen1,2, Ingram McCall1,
and Brenda Cleveland3
Figure 1. Prolonged leaf wetness can lead to leaf death due to
Botrytis. Time irrigation such that the leaves dry out as quickly
as possible and do not remain wet for long periods of time.
The licorice plant (He-
lichrysum petiolare) is a
South African native that
also is appropriately named
trailing dusty miller. The
foliage is silver and it has a
soft arching growth habit.
There is limited produc-
tion information available
about Helichrysum. On-
line, the cultural sheets
from Ball Seed Company
and Proven Winners include
the most extensive infor-
mation (see links in addi-
tional information section
below).
2014 Sponsor
1 NC State University
2 Former NC State University
graduate student, currently
completing his PhD at Purdue
University.
3 NCDA&CS Agronomic Division
© Garrett Owen
© Brian Whipker
2
e-GRO Alert - 2014
e-GRO Alert
www.e-gro.org
CONTRIBUTORS
Dr. Nora Catlin
Floriculture Specialist
Cornell Cooperative Extension -
Suffolk County
nora.catlin@cornell.edu
Dr. Kristin Getter
Floriculture Outreach Specialist
Michigan State University
getterk@msu.edu
Dan Gilrein
Entomology Specialist
Cornell Cooperative Extension -
Suffolk County
dog1@cornell.edu
Dr. Brian Krug
Floriculture Ext. Specialist
Univ. New Hampshire
brian.krug@unh.edu
Dr. Joyce Latimer
Floriculture Extension & Research
Virginia Tech
jlatime@vt.edu
Dr. Roberto Lopez
Floriculture Extension Specialist &
Research
Purdue University
rglopez@purdue.edu
Dr. Paul Thomas
Floriculture Extension & Research
University of Georgia
pathomas@uga.edu
Dr. Brian Whipker
Floriculture Extension & Research
NC State University
bwhipker@ncsu.edu
Copyright © 2014
are listed, no discrimination is intended and no endorsement,
guarantee or warranty is implied by the authors, universities
or associations.
The plant is relatively pest
free, but aphids, leafmin-
possible. Disease wise,
root rot (Pythium) can be
problematic under cloudy
conditions when the plants
are overhead irrigated.
Botrytis can occur on wet
foliage during overcast
conditions and in high
humidity environments.
As reported in e-GRO Alert
3.12, low pH induced mi-
cronutrient phytotoxicities
can occur.
The focus of this article is
to provide a photograph-
based diagnostic guide to
production disorders of
licorice plant. Table 1
contains a listing of the
primary disorders reported
for Helichrysum. Table
2 contains recommended
leaf tissue nutrient levels.
Thanks is expressed to the
Dümmen Group for sup-
plying cuttings, the North
Carolina Department of
Agriculture and Consumer
Services Agronomic Divi-
sion for donating the tis-
sue analysis tests, and the
Fred C. Gloeckner Founda-
tion for support of plant
nutrition research at North
Carolina State University.
Additional Helichrysum Production Information
Proven Winners
http://www.provenwinners.com/plant/43572/culture
http://www.provenwinners.com/plant/43573/culture
Ball Seed Company
http://www.ballseed.com/Growers/plant_info.
aspx?phid=032001124002920
GPN Vegetative Matters
Helichrysum_Vinca.pdf
Ball Redbook, Volume 2, 18th Edition
Helichrysum, p. 438-439.
3
e-GRO Alert - 2014
NC STATE UNIVERSITY
Floriculture
Cooperating Universities
In cooperation with our
local and state greenhouse
organizations
© Brian Whipker © Garrett Owen
Figure 2. Helichrysum plants are extremely prone to Pythium when
the foliage is kept wet when rooting or during overcast conditions
and in high humidity environments such as during propagation.
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e-GRO Alert - 2014
Figure 3B. Over time, the black leaf spotting on the lower foliage expands to cover
most of the leaf. With advanced symptoms, the entire leaf turns yellow.
Figure 3A. Initial symptoms of low pH induced micronutrient toxicity is black leaf
spotting on the lower foliage.
© Brian Whipker © Brian Whipker
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e-GRO Alert - 2014
Table 1. Troubleshooting disorders of licorice plant (Helichrysum petiolare).
Damage Possible Cause Management
Plant Wilting / Death Root Rot (Pythium)
(Root death can be observed)
(Fig. 2)
Avoid excessive irrigations that allow the sub-
strate to remain wet. Apply protective fungicides
if needed.
Stem Rot (Rhizoctonia)
(Web-like growth may be visible
at soil line)
Leaf Discoloration / Plant Death Cold Temperatures / Frost Dam-
age
Cold temperatures will result in leaf scorch and
plant death. Shipping temperature should be
>40F (>4C).
Leaf Discoloration / Death Gray Mold (Botrytis) (Fig. 1) Avoid overhead irrigation that keeps the foliage
wet. Apply protective fungicides if needed.
Upper Leaf Yellowing High pH Symptoms occur when the pH is greater than 6.5.
Maintain the substrate pH between 6.0 and 6.5.
Lower Leaf Yellowing Low Nitrogen / Low EC
(Fig. 4)
Maintain the EC between 0.6 to 0.9 mS/cm based
on the 1:2 extraction method.
[That converts to a SME range of 1.3 to 2.0 mS/
cm or a PourThru range of 2.0 to 3.0 mS/cm
(based on top irrigation)].
Lower Leaf Black Spotting (small
pin-point spots)
Low pH
(Fig. 3)
Symptoms occur when the pH is less than 5.4.
Tissue levels of >500 ppm iron (Fe) and elevated
manganese (Mn) are typical when the pH is too
low. Maintain the substrate pH between 6.0 and
6.5.
Poor Branching Low Nitrogen / Low EC
(Fig. 4)
Maintain the EC between 0.6 to 0.9 mS/cm based
on the 1:2 extraction method.
Excessive Growth Low Light / Overwatering / Late
Florel Applications / High NH4-N
fertilization
Modify production practices to correct excessive
stretch.
Lower Leaf Black Spotting (large
concentric ring spots)
Alternaria Leaf Spot Apply protective fungicides if needed.
Leaves sticky, black sooty mold may
be present. Small soft-bodied insects
present.
Aphids
(Fig. 5)
diagnosis. Apply insecticides if needed.
Leaves sticky, black sooty mold may
be present. Small white insects and
cotton-like masses present.
Mealybugs
(Fig. 6)
Inspect the plants (growing tips, stems, and
Discard plants if the infection is heavy. Apply
insecticides if needed.
Leaves sticky, black sooty mold may
be present. Small white insects that
diagnosis. Apply insecticides if needed.
Leaves with distortion. Small black
fecal deposits present.
Western Flower Thrips -
nosis. Apply insecticides if needed.
Leaves with silver tunnels beneath the
leave surface.
Leafminers
diagnosis. Apply insecticides if needed.
Leaves with chew holes Caterpillars
diagnosis. Apply insecticides if needed.
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e-GRO Alert - 2014
Figure 4A. Lower leaf yellowing can occur when the fertilization rate is too low. This plant had
a PourThru EC reading of 1.28 mS/cm. These values convert to 0.85 mS/cm for the SME meth-
od or 0.39 mS/cm based on the 1:2 extraction method. The recommended EC range is 0.6 to 0.9
mS/cm based on the 1:2 extraction method. [That converts to a SME range of 1.3 to 2.0 mS/cm
or a PourThru range of 2.0 to 3.0 mS/cm (based on top irrigation).]
Figure 4B. With advanced symptoms of low EC, leaves turn from a pale green to yellow, and
ultimately necrotic.
© Brian Whipker© Brian Whipker
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e-GRO Alert - 2014
Figure 5. Aphids will feed on the licorice plant. Black aphids can be observed on the stems.
Figure 6. Mealybugs have been observed feeding on the licorice plant. The white insects and
© Brian Whipker© Brian Whipker
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e-GRO Alert - 2014
Scheduling
Finishing times range from 5 to 6 weeks
for 1 liner per 4”, 5” and quart pots to 6
to 8 weeks for 1 to 2 liners per 6” pots.
Transplant 3 to 4 liners per 10” hanging
basket. Helichrysum is most often used in
mixed containers and not singly in hang-
ing baskets.
Temperatures
Rooting temperatures: 65 to 72°F (18 to
22°C). Air temperature: Day 75 to 80°F
(24 to 26°C)/ Night 68 to 70°F (20 to
21°C).
Growing temperatures:
Days: 65 to 75°F (18 to 24°C)
Nights: 62 to 65°F (16 to 18°C)
Holding temperatures: 40 to 50°F (4 to
10°C)
Propagation
Stick one cutting per 72-cell tray and
estimated time from stick to transplant
is 3 to 4 weeks. Ball Seed Company rec-
ommends the following culture during
propagation, apply a foliar feed of 50
to 75 ppm N from a 20-10-20 as soon as
foliage looses the silvery color. Apply mist
and keep the rooting substrate uniformly
moist. Callus formation will occur 5 to 7
days after sticking and root development
will occur 7 to 14 days later.
During root development, increase light
levels and reduce mist frequency to allow
rooting medium to dry out. Apply a foliar
feed of 100 ppm N from 15-0-15, alter-
nating with 20-10-20, and increasing the
rate to 200 ppm N during later stages of
root development. Harden cuttings 7 days
prior to transplant to reduce transplant
shock by increasing light levels and elimi-
nating mist. Applying Florel to cuttings
during hardening off will encourage sub-
sequent branching.
Light
Helichrysum prefer medium to high light
levels. Low light levels will result in
stretched growth and lighter green foli-
age. The silver foliage color is enhanced
with higher light levels.
Irrigation
Problems related to excessive irrigations
or wet foliage is the major production
challenge of this plant. Excessive sub-
strate moisture levels can lead to Pythi-
um problems and wet foliage can lead to
Botrytis infections. Allow the substrate
to dry slightly between irrigations. Also
avoid prolonged leaf wetting by irrigat-
ing in the morning so the leaves have a
chance to dry off.
Substrate
Use a well-drained, disease-free, soil-
less substrate with a pH of 6.0 to 6.5. At
substrate pH levels below 5.4, low pH in-
duced micronutrient toxicities can appear
as lower leaf black spotting.
Fertilization
Fertilization rates of 150 to 200 ppm N
are recommended. Pale green lower
leaves are an indication that the fertiliza-
tion levels are too low. Maintain the EC
between 0.6 to 0.9 mS/cm based on the
1:2 extraction method. That converts to a
SME range of 1.3 to 2.0 mS/cm or a Pour-
Helichrysum petiolare Growing Tips
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e-GRO Alert - 2014
Thru range of 2.0 to 3.0 mS/cm (based
on top irrigation). Recommended tissue
values are listed in Table 2. If iron chlo-
rosis due to high substrate pH becomes
a problem during production, apply iron
chelate.
Pinching / PGRs
Seed types may not require pinching.
-
ing two weeks after transplant (once
roots have reached the container side) to
improve overall plant form. Plants can
be trimmed back if needed.
PGR recommendations vary by company.
Therefore, conduct your own trial to de-
termine optimal rates. PGRs may not be
required if pinching is used.
Ball Seed Company recommends a foliar
spray tank mix of Daminozide (B-Nine/
Dazide) at 2,500 ppm with Paclobutrazol
(Bonzi,/Paczol/ Piccolo/Piccolo 10XC) at
30 ppm, applied three weeks after trans-
plant. It is reported to keep the plants
more compact and enhances the silver
foliage coloration.
Florel is effective in enhancing branching,
but the last application should occur 8
weeks prior to sale.
A trial at the University of Florida studied
paclobutrazol preplant liner soaks. For
Helichrysum ‘White’ a 2 ppm soak con-
trolled growth by 42% when compared to
the untreated plants. A concentration
of 8 ppm was effective for Helichrysum
‘Petite’. Even the lowest rate of 2 ppm
was excessive for ‘Lemon’ and ‘Splash’.
cultivar and keep in mind these rates are
based on Florida growing conditions. Mid-
Atlantic growers would be well advised to
start their trials with using half rates and
more northern growers should begin with
quarter rates.
Researchers at the University of Florida
also studied paclobutrazol substrate
drenches. The plants were grown for
four weeks and pinched. One week later
the paclobutrazol drench applications
were made. They recommended for ‘Lico-
rice’ a 2 ppm drench which gave optimal
growth control.
Pests/Disorders
Overall this plant is pest free. Because
it is native to more arid conditions, the
primary problems reported are related to
over irrigation (Pythium) and prolonged
moisture on the foliage (Botrytis). A di-
agnostic key to disorders is listed in Table
1.
Insects
Insects are not a serious problem on
Helichrysum. Infestations by aphids,
leafminers, mealybugs, thrips, caterpil-
Diseases
Botrytis can be problematic if water is
allowed to remain on the leaves for long
periods of time. Pythium problems can
occur if the plants are over irrigated.
Other diseases reported include Alter-
naria and Rhizoctonia.
Nutritional
Pale green to yellow foliage will occur if
the fertilization rate is too low. Use fertil-
ization rates of 150 to 200 ppm N. Low
pH induced micronutrient toxicities can
occur if the substrate pH is below 5.4.
Maintain the pH between 6.0 and 6.5 to
avoid this disorder.
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e-GRO Alert - 2014
Table 2. Leaf tissue nutrient analysis results for
the licorice plant (Helichrysum).
Element
Most Recently Matured Leaves
(4 week old plants)
Nitrogen (%) 2.29-3.80
Phosphorus (%) 0.23-0.37
Potassium (%) 1.69-2.69
Calcium (%) 0.65-0.70
Magnesium (%) 0.31-0.32
Sulfur (%) 0.24-0.26
Sodium (%) 0.28-0.64
Iron (ppm) 99.8-330
Manganese (ppm) 160-230
Zinc (ppm) 41.1-46.2
Copper (ppm) 5.82-11.9
Boron (ppm) 21.3-36.7
Actively growing plants fertilized with a range of 150 to 250 ppm
N.
Physiological
None reported.
Shipping
Plants can be shipped at 40 to 50°F (4 to
10°C). Avoid prolonged periods of low
light or high humidity to prevent Botrytis
problems. Plants are prone to low tem-
perature damage.
Planting
Helichrysum prefer a dry, sunny growing
location. Plants do not perform well in
areas with high humidity or a rainy envi-
ronment.