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y3,(7 MICRONUTRIENTS IN TROPICAL FOLIAGE PRODUCTION
Richard T. Poole and Charles A. Conoverl
University of Florida, IFAS
Agricultural Research C aer Apopka
Research Report RH- J3-17
Micronutrients (also called minor, trace or secondary elements) are
needed in small, but critical amounts, by green plants and include boron
(B), chlorine (Cl), copper (Cu), iron (Fe), manganese (Mn), molybdenum
(Mo), and zinc (Zn). Micronutrients are recognized as an important part
of foliage production and are commonly used in fertilization programs.
The need for micronutrient additions to organic soil mixtures has been
well established in many areas of crop production. Present micronutrient
recommendations for foliage growers are designed to provide a form of
"crop insurance" for those who have experienced problems with micro-
nutrient deficiencies or want to prevent their development.
With increased usage of micronutrients by foliage growers some guide-
lines seem necessary, and the following points are designed to prevent
crop damage from excessive applications of any micronutrient mixture as
well as provide minimum required amounts. Additions of micronutrients to
soil mixtures or their inclusion in fertilizer programs require caution
because high levels are sometimes toxic. Boron and Mn have been shown to
be phytotoxic to many plant genera and have been implicated in recent
foliage crop damage reports.
When recommended rates of micronutrients are incorporated into the
soil medium, fertilizers with micronutrients are not needed unless plants
remain in the pots for more than 6 months. Micronutrients should not be
incorporated into soil mixtures prior to steam sterilization because
steaming increases availability. When including sludge or other organic
fertilizers containing micronutrients in soil mixtures, reduce additions
of subsequent micronutrients.
Growers who tank mix their own fertilizer formulations from single
components, such as ammonium nitrate, potassium nitrate and phosphoric
acid, can utilize a commercial soluble micronutrient additive. Such
commercially prepared micronutrient mixtures are sometimes high in certain
elements such as B, which limits their use because the correct B level
does not provide desired levels of other micronutrients.
Although deficiency symptoms vary for different crops, generalizations
may be useful in diagnosing specific problems. Microelement deficiencies
are observed in the newer leaves, while macroelement (N, P, K, Mg and S)
deficiencies are observed in the lower leaves or the entire plant.
Boron The bud and new leaves turn light green in color, become rigid and
brittle with epidermal cracking. Terminal buds eventually die if corrective
action is not taken.
Professor, Plant Physiology and Professor and Center Director, Agricultural
Research Center-Apopka, respectively.
Chlorine Because of C1 in water and fertilizer, C1 deficiency has not
been reported on foliage plants.
Copper Young terminal leaves may lack turgidity, showing a wilted effect.
Chlorosis should be evident. Upper leaves are often cupped with a marginal
burn. Severe deficiency results in tip dieback.
Iron Interveinal chlorosis develops in new leaves, eventually leaves
become completely yellow, sometimes white.
Manganese Interveinal areas near edges of terminal leaves become chlorotic
but appear to be more of a checkered or striped pattern than Fe.
Molybdenum Older leaves become mottled, then younger leaves. Leaves curl
inward and necrosis occurs.
Zinc New leaves small, hence its common name "little leaf disease".
eventually become chlorotic, then necrotic.
Boron The range between deficiency and toxicity is extremely narrow for B.
Leaves become chlorotic at the tip and chlorosis progresses along the tip
margins. Eventually necrotic areas occur which may fall from the leaf when
toxicity is severe. B toxicity damage has been observed on foliage plants.
Chlorine Excess of C1 results in "soluble salts" injury, a burning of the
root tips and marginal necrosis of older leaves.
Copper Excess Cu produces symptoms similar to Fe deficiency.
Iron High levels of Fe depress Mn absorption resulting in symptoms similar
to Mn deficiency.
Molybdenum Excess application of Mo results in chlorosis similar to Fe
deficiency, also distortion of leaves.
Manganese Excess Mn results in stunted growth. Chlorosis similar to Fe
deficiency occurs, then tipburn of the leaf.
Zinc Heavy application of Zn also suggests Fe deficiency.
Abnormal symptoms resembling micronutrient deficiencies or toxicities
can be caused by many other factors. Pesticides, particularly herbicides,
when applied improperly cause damage to foliage plants which may be confused
with improper usage of microelements. High soluble salts, high or low
temperatures, insects, nematodes and diseases are other confusing factors.
Although micronutrients are essential for production of foliage plants,
research has indicated that supplemental micronutrients are required in low
quantities or not at all depending on their level in the potting medium and
nutrition of the stock plant. Philodendron scandens oxycardium and Epipremnum
aureum (pothos) grown for six months in solution culture without essential
elements expressed only mild deficiency symptoms of Fe and no lack of growth
or chlorosis in plants that were.grown without Cu, Mn or Zn. Aphelandra
squarrosa 'Dania', Brassaia actinophylla and Philodendron scandens oxycardium
grew for three months equally as well as in a potting medium of peat/sand
without additional micronutrients as with micronutrients. Table 1 shows the
effect of additional micronutrients on quality of foliage plants grown for 4
months in a mix of peat/bark/shavings without or with supplemental micro-
nutrients. There was a slight increase in quality of some of the plants in
response to the incorporation of the micronutrients.
The pH of the soil can influence availability of microelements. Fe and
Mn are readily available at pH 5, but solubility (availability) decreases as
the pH approaches 7 and deficiency symptoms, particularly Fe, may be noticed.
Zn, Cu and B availability is slightly reduced with an increase in pH. How-
ever, Mo is more easily obtained by plants as pH increases.
Chelated metals are frequently used to supply microelements to plants.
Chelates (Greek for claw) are organic compounds which contain metal ions.
The chelate prevents the metal from completing with the soil, thus maintain-
ing the metal in a form available to plants.
Sources of Microelements
Microelements are found in the irrigation water, growing medium and some-
times in fertilizers supplying N,P,K,Ca or Mg. Many fungicides contain Cu,
Fe, Mn and Zn. When these sources do not supply adequate microelements, they
must be added. Quantities (percentage) of microelements as listed on the
fertilizer bag are misleading when quantities are given as the oxides. The
actual amount of the plant nutrient is therefore less. Conversion factors
which are needed to determine the actual amount of microelements purchased
are listed below.
A survey of recommendations to prevent microelement deficiency reveals a
wide disparity in amounts of microelements suggested, indicating a wide range
of microelement availability at which plants will grow satisfactorily. A
satisfactory range for tissue content of foliage plants is Cu = 10-60, Fe =
50-300, Mn = 50-300 and Zn = 25-200 parts per million of dry weight.
Foliage plants have been grown satisfactorily without supplemental appli-
cations of microelements. However, if a deficiency is suspected, and/or
preventative measures are desired, the rates in Table 2 are suggested. Table 3
lists composition of some micronutrient sources. Soil incorporation or drench-
ing is preferred for preventing micro-deficiencies, while spray followed by
drench is the best method of correcting existing deficiencies.
1. Cibes, H. and G. Samuels. 1960. Mineral deficiency symptoms displayed
by Dracaena godseffianaand Dracaena sanderiana grown under controlled
conditions. Univ. of Puerto Rico Ag. Expt. Station Technical Paper 29.
2. Conover, C. A. and R. T. Poole. 1972. Influence of propagation bed
nutritional amendments on selected foliage plants. Proc. Fla. State
Hort. Soc. 85:392-394.
3. Conover, C. A. and R. T. Poole. 1973. Factors influencing micron
use in tropical foliage production. Univ. of Fla. ARC-Apopka Mimeo
4. Conover, C. A., D. W. Simpson and J. N. Joiner. 1975. Influence of
micronutrient sources and levels on response and tissue content of
Aphelandra, Brassaia and Philodendron. Proc. Fla. State Hort. Soc.
5. Dickey, R. D. and J. N. Joiner. 1966. Identifying elemental defic
in foliage plants. Southern Florist and Nurseryman 79(20):38,42-43.
6. Joiner, J. N. and W. E. Waters. 1970. The influence of cultural condi-
tions on the chemical composition of six tropical foliage plants. Proc.
Trop. Reg. Amer. Soc. Hort. Sci. 14:254-267.
7. Poole, R. T. and C. A. Conover. 1974. Nutritional studies of three
foliage plants. SNA Research Journal 1(2):17-26.
8. Samuels, G and H. Cibes. 1953. Iron chlorosis on Dracaena sanderiana.
Univ. of Puerto Rico J. of Agr. 37(4):265-272.
Table 1. Quality (1 = poor, 5 = excellent) of foliage plants grown in a peat/
bark/shaving mix for 4 months.
Micronutrient Aphelandra Calathea Calathea Brassaia Chrysa
mix Ibs/yd squarrosa clossonii roseopicta actinophylla lutescens
Control 4.0 3.0 3.0 4.7 3.2
Esmigran 3 4.2 2.8 3.5 4.7 3.3
Esmigran 6 4.5 2.8 3.8 4.3 3.3
Perk 1.5 4.0 3.5 3.8 4.7 4.0
Perk 3 3.8 3.7 3.7 4.2 4.3
Micromax 1.5 4.3 3.2 3.8 4.4 4.0
Micromax 3 4.7 2.8 3.7 4.8 4.7
Table 2. Suggested application rates for micronutrients.
Spray Soil Soil
application drench incorporation
Element g/gal ppm g/100 ft g/yd
B .005 1 0.1 0.1
Cu .05 10 1.0 1.0
Fe .50 100 10.0 10.0
Mn .25 50 5.0 5.0
Mo .005 1 0.1 0.1
Zn .2 40 4.0 4.0
Table 3. Percent composition of micronutrient sources.
Esmigran FTE 503 Micromax Perk Stem Vigoro
B 0.02 0.8 0.1 0.02 1.45
Cu 0.3 1.5 0.5 0.5 3.2 0.4
Fe 2.0 14.0 12.0 9.0 7.5 6.3
Mo 0.0006 0.07 0.005 0.003 0.046 0.001
Mn 0.5 5.0 2.5 2.0 8.2 3.1
Zn 1.0 5.0 1.0 1.0 4.5 1.6
B203 X 0.31 = B B X 3.2 = B203
CuO X 0.80 = Cu Cu X 1.2 = CuO
Fe203 X 0.70 = Fe Fe X 1.4 = Fe203
MnO X 0.77 = Mn Mn X 1.3 = MnO
Mo03 X 0.67 = Mo Mo X 1.5 = MoO3
ZnO X 0.80 = Zn Zn X 1.2 = ZnO