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5--( UNIVERSITY OF
Institute of Food and Agricultural Sciences
Gulf Coast Research and Education Center
5007 60th St. E., Bradenton, FL 34203
Bradenton GCREC Research Report
BRA-1995-1 (January 1995)
CONTROL OF ZINNIA LEAF TIPBURN BY CALCIUM SPRAYS
S. S. WOLTZ, J.
APPLICATIONS OF CALCIUM;
MOLD PREVENTION ,,ston Science
HARBA sity o oia
UnWersit ot oi*da
AND B. K.
GCREC Research Report BRA1995-1
Control of Zinnia Leaf Tipburn by Calcium Sprays and Post-Planting
Soil Applications of Calcium; Role in Gray Mold Prevention
S. S. Woltz, J. P. Jones, and B. K. Harbaugh'
Gulf Coast-Research and Education Center
University of Florida, IFAS
5007 60th Street East
Bradenton, FL 34203
Leaf tipburn and bract necrosis, a similar disorder, are frequently associated
with a localized, temporary calcium deficiency (3,4,6,7,8,9,12). The supply of
calcium reaching the rapidly expanding tissue oftentimes does not keep up with
the calcium requirement for normal development. The soil solution supply may be
inadequate, movement with the transpiration stream to developing parts may be
limited by environmental conditions unfavorable to higher transpiration rates,
translocation from older leaves is very limited, and the chemical activity of the
calcium ion is low, causing it to accumulate in poorly soluble compounds and to
be readily immobilized in soil and plant. Thus, there are many situations where
calcium deficiency is encountered when the soil and plant chemical analyses would
seem to indicate that a deficiency should not be found. Solutions to the problem
lie in the field of plant nutrition wherein we use various methods to get the
calcium to the location where it is needed. Frequently a grower will find that
a potting mix he/she is using is in need of a post-planting adjustment of pH or
available calcium supply; or a foliar spray may be used alone or in combination
with soil applications when the problem is identified after the crop culture is
in progress. In some cases of calcium deficiency,- soil applications are not
adequate and sprays of soluble calcium are required to prevent further occurrence
of the disorder associated with a low calcium movement to a rapidly developing
Low levels of calcium in plant tissue are frequently associated with enhanced
Botrytis activity (2,10,11). The involvement of other nutrients and enzyme
mechanisms are also reported (1,5). Increased levels of organic acids in tissue
during disease development and progression favor the maceration of the tissues
while calcium, especially in its role in pectin chemistry counteracts the effects
of the organic acids. Pectin compounds in cell walls are more easily attacked by
pectin-dissolving enzymes when calcium levels are minimal. The availability of
nutritional compounds for the Botrytis in initiating invasion is much enhanced
under low calcium conditions when electrolyte leakage and metabolite release
occur in the tissues softened by the deficiency. Sugars are important in favoring
germination of spores and subsequent tissue invasion.
Objectives in the research to be reported include 1) the elucidation of the basic
cause of zinnia leaf tipburn, 2) development of methods of prevention when the
deficiency is discovered during growing operations, and 3) relating the leaf
tipburn condition to aggravation of the Botrytis Gray Mold disease problem.
'Visiting Professor, Plant Pathologist, and Floriculturist, respectively.
Materials and Methods
'Rose Pinwheel' zinnias were grown in the greenhouse in 5-inch plastic pots
containing a standard mix consisting of 50% by volume each of Canadian peat and
horticultural vermiculite. The mix was amended with 5 lbs. per cu. yd. of
Osmocote 14-14-14 plastic coated fertilizer, 2.5 lbs. per cu. yd. of calcium
carbonate very fine powder, and 1.2 lbs. per cu. yd. of a complete micronutrient
mix, Micromax. The lime rate was kept low to favor the development of calcium
deficiency to test the hypothesis that post-planting methods would be effective
in preventing further development of the disorder. Calcium treatments included
a spray of calcium chloride (0.8 lbs. per 100 gallons) applied three times the
first week after appearance of deficiency symptoms and once weekly thereafter to
the end of the experiment. The low rate of calcium chloride was used because of
unusually high susceptibility of zinnia to spray injury from the compound (14).
At the initiation of calcium treatments, one-time applications were also made to
the pots of calcium sulfate and calcium carbonate at respective rates of 0.75 and
0.5 grams per pot(corresponding to 0.6 and 0.4 lbs. per cu. yd. of mix in the
pots), combined factorially with the spray. The experiment was begun 7-18-93, and
differential treatments were started 3 weeks later after the appearance of the
first symptoms of zinnia leaftip burn. This experiment was a repetition of
previous experiments with similar results; only the single experiment is being
Results and Discussion
One week after spraying calcium three times on the plants showing leaf tipburn,
the new growth was free of tipburn (Table 1). A later reading at 19 days showed
that the CaC03 applied to the pot was having an effect in reducing tipburn
slightly. At 24 days the effect was more evident and statistically significant.
CaS04 was less effective in speed of reaction, but this is probably due in part
to the fact that the fineness of division of the CaS04 was not as great as that
of the CaCO3. Media pH's were low as shown in Table 1, although the CaCO3 did
raise the media reaction to near pH 6.0. The effect of reducing spray frequency
from 3 to 1 times weekly appears to be a decreased degree of control of the
tipburn on the rapidly emerging new leaves.
Leaf surface solution pH's (13) were not greatly different in comparisons of the
6 treatment combinations but had statistical significance, notably showing a
higher pH with the CaC03 treatments. This slight elevation of pH might be of
benefit in retarding the action of Botrytis in tissue maceration as discussed
above in connection with the production of organic acids by Botrytis.
Observations of Botrytis on 'Rose Pinwheel' zinnia in cool weather indicated that
the infections occurred initially in association with tipburn leaves at the
boundary between living and necrotic tissue; these cases were not definitely
linked to calcium deficiency as the cause of the tipburn.
Summary: Calcium deficiency was shown to be the basic cause of a leaf tipburn of
zinnia. Further development of the deficiency on the newer leaves, was stopped
quickly in the developing leaves by spray applications of calcium chloride. The
deficiency was corrected more slowly by soil applications of a fine calcium
carbonate powder or calcium sulfate (gypsum). The fine powder of calcium
carbonate may be suspended in water and with continuous agitation, applied as a
soil drench effectively and safely to correct a condition that ordinarily would
be avoided pre-planting by adequate and effective liming of the media. Most
effective control of the deficiency would require initiating soil and spray
treatments together when the problem is diagnosed. Leaf tipburn should be
avoided, even though moderate in effect per se, because it provides perfect
conditions for Botrytis Gray Mold establishment.
1. Edlich, W., G. Lorenz, H. Lyr, E. Nega, and E. H. Pommer. 1989. New
aspects on the infection mechanism of Botrytis cinerea Pers. Neth. J.
Plant Path. 95: (Suppl. 1:53-62).
2. Elad, Y., and H. Volpin. 1988. The involvement of ethylene and calcium in
gray mold of Pelargonium, Ruscus, and rose plants. Phytoparasitica 16:119-
3. Harbaugh, B. K., and S. S. Woltz. 1986. Calcium sprays prevent marginal
bract necrosis. Greenhouse Grower 4:14, 17, 64.
4. Harbaugh, B. K., and S. S. Woltz. 1989. Fertilization practice and foliar-
bract calcium sprays reduce incidence of marginal bract necrosis of
poinsettia. HortScience 24:465-468.
5. Hobbs, E. L., and W. E. Waters. 1964. Influence of nitrogen and potassium
on susceptibility of Chrysanthemum morifolium to Botrytis cinerea.
6. Krug, von H., H. J. Wiebe, and A. Jungk. 1972. Calciummangel an Blumenkohl
unter konstanten Klimabedingungen. Z. Pflanzen. und Boden. 133:213-226.
7. Mason, G. F., and C. G. Guttridge. 1975. The influence of relative
humidity and nutrition on leaf tipburn of strawberry. Scientia. Hort.
8. Maynard, D. N., D. C. Warner, and J. C. Howell. 1981. Cauliflower leaf
tipburn: a calcium deficiency disorder. HortScience 16:193-195.
9. Rosen, C. J. 1990. Leaf tipburn in cauliflower as affected by cultivar,
calcium sprays, and nitrogen nutrition. HortScience 25:660-663.
10. Stall, R. E. 1963. Effects of lime on incidence of Botrytis gray mold of
tomato. Phytopath. 53:149-151.
11. Stall, R. E. 1991. Gray mold. pp. 16-17 in: Jones, J. B., J. P. Jones, R.
E. Stall, and T. A. Zitter. (eds.) Compendium of tomato diseases.
12. Woltz, S. S., and B. K. Harbaugh. 1986. Calcium deficiency as the basic
cause of marginal bract necrosis of 'Gutbier V-14 Glory' poinsettia.
13. Woltz, S. S. 1994. Leaf surface solution (LSS) and spray pH values
relative to spray efficacy and phytotoxicity. Bradenton GCREC Res. Report
14. Woltz, S. S. 1994. Stomatal liquid infiltration (SLI) test, crop culture,
and air pollution effects. Bradenton GCREC Res. Report BRA1994-19.
Table 1. Effects of calcium
on new zinnia leaf
spray and soil applications of calcium sources
tipburn ratings and pH of leaf surface solution
Treatmentsy New leaf tipburn LSS pHz Media pH
-- Days after treatment--
CaC12 CaSO CaCO 8 19 24 14 24
spray lbs/ Ibs/
Ibs/ cu. cu.
100 gal yd. yd.
S- 4.17a 5.50a 4.50a 6.27c 5.26b
0.6 3.33a 5.33a 5.50a 6.17c 4.93b
0.4 3.67a 3.67ab 2.17b 6.47ab 6.13a
0.8 0.00b 2.17 2.67b 6.30bc 5.00
0.8 0.6 0.00b 1.17c 1.67' 6.47ab 4.75C
0.8 0.4 0.00b 0.33c 0.30c 6.57a 5.80a
wRatings of new leaf tipburn 0-10 where 0 = no necrosis, 10 = most severe
necrosis (leaf tipburn).
XNumbers within columns followed by different letters are significantly
different at the 5% level, Duncan's test.
YTreatments shown were begun 21 days after planting; days after treatment were
counted from that date. Spray was applied to plants 3 times the first week
and once weekly thereafter to the end of the experiment. CaC12 and CaSO4
were worked into the surface of media in pots.
ZLSS pH = leaf surface solution pH of deionized water equilibrated with the
underside of the leaves.
The Gulf Coast Research and Education Center
The Gulf Coast Research and Education Center is
a unit of the Institute of Food and Agricultural Sci-
ences, University of Florida. The Research Center
originated in the fall of 1925 as the Tomato
Disease Laboratory with the primary objective of
developing control procedures for an epidemic out-
break of nailhead spot of tomato. Research was ex-
panded in subsequent years to include study of sev-
eral other tomato diseases.
In 1937, new research facilities were established
in the town of Manatee, and the Center scope was
enlarged to include horticultural, entomological, and
soil science studies of several vegetable crops. The
ornamental program was a natural addition to the
Center's responsibilities because of the emerging in-
dustry in the area in the early 1940's.
The Center's current location was established in
1965 where a comprehensive research and extension
program on vegetable crops and ornamental plants is
conducted. Three state extension specialists posi-
tions, 16 state research scientists, and two grant
supported scientists from various disciplines of
training participate in all phases of vegetable and
ornamental horticultural programs. This interdisci-
plinary team approach, combining several research
disciplines and a wide range of industry and faculty
contacts, often is more productive than could be ac-
complished with limited investments in independent
The Center's primary mission is to develop new
and expand existing knowledge and technology, and
to disseminate new scientific knowledge in Florida, so
that agriculture remains efficient and economically
The secondary mission of the Center is to assist
the Cooperative Extension Service, IFAS campus
departments, in which Center faculty hold appropri-
ate liaison appointments, and other research centers
in extension, educational training, and cooperative
research programs for the benefit of Florida's pro-
ducers, students, and citizens.
Program areas of emphasis include: (1) genetics,
breeding, and variety development and evaluation;
(2) biological, chemical, and mechanical pest manage-
ment in entomology, plant pathology, nematology,
bacteriology, virology, and weed science; (3) produc-
tion efficiency, culture, management, and counteract-
ing environmental stress; (4) water management and
natural resource protection; (5) post-harvest physiol-
ogy, harvesting, handling and food quality of horti-
cultural crops; (6) technical support and assistance to
the Florida Cooperative Extension Service; and (7)
advancement offundamental knowledge ofdisciplines
represented by faculty and (8) directing graduate
student training and teaching special undergraduate
l The Institute of Food and Agricultural Sciences,
University of Florida.
" A statewide organization dedicated to teaching,
research and extension.
D Faculty located in Gainesville and at 13 research
and education centers, 67 county extension
offices and four demonstration units throughout
D A partnership in food and agriculture, and natural
and renewable resource research and education,
funded by state, federal and local government,
and by gifts and grants from individuals, founda-
tions, government and industry.
Q An organization whose mission is:
Educating students in the food, agricultural,
and related sciences and natural resources.
Strengthening Florida's diverse food and
agricultural industry and its environment
Enhancing for all Floridians, the application
of research and knowledge to improve the
quality of life statewide through IFAS exten-