T UNIVERSITY of
Volume 15, Number 1
Potassium Nutrition in Phaleonopsis
By Lelan Parker
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Juanita Popenoe, Ph.D.
Lelan Parker, M.S.
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A recent study at the Texas Agricul-
tural Research and Extension Center
has shown that Potassium (K) con-
centrations directly affect the
growth ofPhaleonopsis. Bare root,
white-flowered Phalaenopsis Tai-
suco Kochdian clone plants were
imported in late May and potted in a
mix consisting of three parts me-
dium-grade douglas fir bark and one
part each of perlite and coarse Cana-
dian sphagnum peat (by volume) or
in chilean sphagnum moss. Plants
grown in moss produced four to five
leaves, whereas those planted in the
bark mix produced only two to three
leaves. K concentration did not af-
fect the length of the uppermost ma-
ture leaves when grown in the bark
mix. However, plants with an in-
crease in K concentration in bark
mix had increasingly longer and
wider top leaves.
Usually, K deficiency symptoms are
shown in the lower leaves of plants.
In this study, Phaleonopsis K defi-
ciency symptoms appeared after
plants in the bark mix had become
reproductive in November. Death
of lower leaves on K-deficient
plants began in late December when
the flowering stem had reached one-
third to one-half of their final
lengths. It is possible that the K in
the lower leaves of Phaleonopsis
was removed and rearranged to the
developing flower buds. This may
explain the development of yel-
lowed lower leaves originally and
steady yellowing and progressive
death of upper leaves and ultimately
the death of the entire plants.
In certain hybrids of Phaleonopsis,
lower leaf yellowing is a serious
problem. These lower leaves were
found to have extremely low levels
of K. Application of 15N-4.3P-
16.8K or full-strength Johnson's
solution reduced the incidence of
lower leaf yellowing. In this study
plants that received 50 mg/L K,
originally appeared healthy but be-
gan showing symptoms of K defi-
ciency after anthesis. This suggests
that although applying 50 mg/L K
(Continued on page 4)
Red Palm Mite is HERE!, Raoiella indica Hirst, was found in South Florida on a coconut palm
in Palm Beach Gardens on 11/29/07. Suspect samples can be sent to DPI for identification or confir-
mation (Contact Information: http://www.doacs.state.fl.us/pi/plantinsp/piinspectordirectory/
piinsp_map.html). Residents can also contact the DPI helpline for additional information at 888-
397-1517. For more information go to http://mrec.ifas.ufl.edu/lso/RPM/RPM.htm.
The Institute of Food and Agricultural Science (IFAS) is an Equal Employment Opportunity Institution authorized to provide research, educational information and other services only to individuals and
institutions that function without regard to race, color, sex, age, handicap or national origin U S DEPARTMENT OF AGRICULTURE, FLORIDA COOPERATIVE EXTENSION SERVICE, UNIVERSITY
OF FLORIDA, IFAS, FLORIDA A & M UNIVERSITY COOPERATIVE EXTENSION PROGRAM, AND BOARDS OF COUNTY COMMISSIONERS COOPERATING
Stand Up and Be Counted
2007 Census of Agriculture
The 2007 Agricultural Census will be sent out in Janu- know about the current state of Florida nurseries if
ary 2008. The Census of Agriculture is taken every you don't respond to the census.
five years and is a complete count of U.S. farms and
ranches and the people who operate them. The Census You are required by law to respond to the census if it
looks at land use and ownership, operator characteris- is sent to you, even if you don't operate a farm. You
tics, production practices, income and expenditures are considered a farmer if you have $1000 or more of
and many other areas. It is vital that you respond so agricultural products produced and sold, or normally
that our agriculture is counted. Your individual infor- would have been sold, during the census year. Even if
mation is completely confidential, but the data totals you only have a half acre nursery in your backyard, if
are used in so many ways. It is used in community you grossed $1000 or more in sales, you need to fill
planning, lending institution decisions, USDA and out the census. Please stand up, be counted, fill out the
extension staffing, and many other key issues facing 2007 Census of Agriculture and show the importance
you and the community. Florida legislators need to of the nursery and greenhouse industry to the state of
know about nursery and greenhouse production when Florida and the U.S.
shaping farm policies and programs, and they will not
Plant Clinic Problem of the Quarter Aerial
Rhizoctonia or Web Blight. Rhizoctonia is a soil pathogen
that mostly affects roots and stems at the soil line, but when
conditions are humid and warm, and the plants are tight,
this fungus can jump to the leaves and stems. The mycelia
can be seen like a fine brownish webbing in the dead leaves,
and may be confused with spider mite webs. Check out the
other plant clinic samples and diagnoses at http://
Nutrient Deficiencies and Indicator Plants
Adapted from Dr. Paul Fisher's "Put Water and Nutrient BMPs into Practice"
Plants that are especially susceptible to nutrient defi-
ciencies can be used to indicate if your nutrition pro-
gram is lacking. Having a few of these plants in your
beds mixed in with the crop plants will allow your
scouts to quickly check visually to see if the nutrition
program is sufficient. The four most common prob-
lems are high salts, low pH, iron deficiency/high pH,
and low nitrogen/phosphorus.
Plants that quickly show nitrogen and phosphorus de-
ficiency are petunia and chrysanthemum. When nitro-
gen and phosphorus are low, the new growth cannibal-
izes the nutrients already present in the older leaves.
As the nitrogen and phosphorus move up to the new
growth, the older leaves turn yellow and fall off, the
internodes get shorter and the plant starts to look very
pale and ragged and grow slowly.
High salts can be seen by browning on the edges of
the older leaves. The leaves in general look dark
green and there is a lack of leaf expansion. When you
check the roots, you will notice that there are brown
roots. This can allow disease to set into the roots, but
the real problem is high salt. New Guinea impatiens,
ferns and penta are good indicators for high salts.
Low pH (5.5 or less) allows the plant to accumulate
iron and manganese because these become much
more soluble at low pH. You will see necrotic spot-
ting in the older leaves caused by excess manganese
in a few species that show this well. Marigolds, penta
and New Guinea impatiens are excellent indicators of
this problem. When adjusting pH remember that you
need a ratio of Ca:Mg of 2:1. You can raise pH with
potassium bicarbonate at 2 lbs/100 gal in the irriga-
High pH causes iron deficiency because the iron be-
comes unavailable to the plant. The older leaves re-
main relatively green and the younger leaves turn yel-
low. This is because iron is needed for chlorophyll
production, but it cannot be remobilized from the
older leaves. Petunias, nemesia and calibrachoa are
good indicator plants for this problem. If the pH is
too high, you can use fertilizer in which all the nitro-
gen is in the ammonium form this is naturally acidi-
fying. Iron can also be added with red iron se-
questrene 148, this is a more expensive chelated iron,
but it works best and can turn iron deficiency around
within 10 days.
This rose looks like an iron deficiency, but when you
check the roots, there are no roots down into the pot-
ting mix, and the mix is very wet and heavy. The real
problem here is that the substrate is too heavy for the
production practices used. There is not enough air in
the rooting media and the roots cannot take up iron
no matter how much iron or fertilizer is applied.
This poinsettia looks like it is suffering from low pH,
but the real problem is high salts. If you look at the
roots, there are no roots in the bottom of the pot.
Nutrient deficiencies are easy to spot once you know
what to look for. Become familiar with your crop or
indicator plants that will quickly let you know what
the problem is, and check your pH and EC regularly.
(Continuedfrom page 1)
may be adequate for vegetative growth, it was not
high enough for producing quality flowering plants.
Plants grown in sphagnum moss and receiving no K
produced an identical number of new leaves with
similar total length as plants receiving 50 to 500 mg/L
K, but no spiking and flowering took place in these
plants. Noticeable symptoms ofK deficiency were
minimal on these plants. It is not understood why
these plants did not become reproductive. This may
explain grower complaints that sometimes the bare-
root plants, previously produced in moss, received by
growers in the United States did not spike, regardless
of good environmental conditions in the greenhouse
A crop's response to K largely depends on the level of
Nitrogen (N) being applied. Higher N results in a
greater yield response from an increase in K. Plants
used in this study received 200 mg/L K each of N and
Phosphorous (P), which have been reported to pro-
mote fast growth and to produce high-quality
Phaleonopsis. As a result, the responses to K in vege-
tative growth and flowering were likely the true re-
sponses to K amounts. Phaleonopsis responded to
increasing K concentration by increased length and the
diameter of the flower stem, larger flowers and overall
increased quality of the finished product.
For more detailed information on this study refer to
Wang, Yin-Tung, 2007: Potassium Nutrition Affects
Phalenopsis Growth and Flowering, HortScience
Congratulations to PJ Klinger!
Outstanding Agriculturist Award
from the Florida Association of County Agricultural Agents for leadership and support pro-
vided to Agricultural Extension Programming throughout Florida 2007.
2008 Planning Calendar
Links to most programs and agendas may be found at: http//cfextension.ifas.ufl.edu or the UF Extension Calendar at http'/
12-Winter 2008 Turf and Ornamental Pest Management Workshop. Orange County Extension. (407)254-9200.
17-19-TPIE. Ft. Lauderdale, FL. Register at www.tpie.org
24-Dead Palms Tell No Tales. Live Video Program. Lake County Extension office. (352) 343-4101.
26-AGRItunity 2008. Sumter County Extension.
26-Review and Exam Limited Certification Licenses. Orange County Extension. (407) 254-9200.
21-Review and Exam O&T and Private Applicator Licenses. Seminole County Extension.(407) 665-5551.
22-23- Tampa Spring Expo. http://www.tbwg.org/
29-Review and Exam Limited Certification Licenses. Osceola County Extension. (321) 697-3000.