The publications in this collection do
not reflect current scientific knowledge
or recommendations. These texts
represent the historic publishing
record of the Institute for Food and
Agricultural Sciences and should be
used only to trace the historic work of
the Institute and its staff. Current IFAS
research may be found on the
Electronic Data Information Source
site maintained by the Florida
Cooperative Extension Service.
Copyright 2005, Board of Trustees, University
(RLO Effect of Osmocote rate on severity of Xanthomonas
O -9 blight of Dieffenbachia 'Camille'::,
A. R. Chase1
University of Florida, IFAS
Central Florida Research and Education Center Apopka ri .
CFREC Apopka Research Report, RH-90-9
One of the most serious bacterial diseases of Aroids is Xanthomonas blight
caused by X. campestris pv. dieffenbachiae. This pathogen affects most members of
the Aroid family including Aglaonema, Anthurium, Caladium, Dieffenbachia,
Philodendron, and Syngonium. The disease first appears as tiny water-soaked spots
on the edges or in the middle of leaves. These spots rapidly enlarge to form typical
necrotic areas with chlorotic borders and can be confined to leaf margins only or
appear anywhere on the leaf. On Syngonium, symptoms are frequently limited to
interveinal areas while on Philodendron scandens subsp. oxycardium (heart-leaf phily)
symptoms are present on leaf edges giving rise to the common name red-edge disease
on this plant. Dieffenbachia are also affected by Xanthomonas blight and show a
combination of marginal, interveinal and distinctly separate lesions nearly always with
a bright yellow halo surrounding the necrotic areas.
In the past, control of Xanthomonas blight on ornamentals has been marginal
at best when bactericides were employed (1,2). Research on a wide variety of foliage
plants has indicated that use of higher than recommended rates of fertilizer can
reduce plant susceptibility to pathovars of X. campestris. For some of the plants
tested, such as Syngonium (3), the host is not adversely affected by increased fertilizer
levels, while on other plants, such asAnthurium (5), the host is damaged when higher
than recommended rates of fertilizer are employed. The following report
summarizes research performed to evaluate the potential for use of fertilizer to
reduce severity of Xanthomonas blight on Dieffenbachia maculata cv. Camille.
Materials and Methods
Plant production. Rooted cuttings of Dieffenbachia maculata cv. Camille,
obtained from commerical producers, were employed in two tests performed between
3 October 1989 and 28 March 1990. Plants were grown in 6 inch pots using a steam-
treated medium consisting of Canadian peat and pine bark (1:1, by volume). Light
levels ranged from 2000 to 2600 ft-c. with temperatures between 65 and 90 F. Ten
plants were used for each of eight rates of Osmocote 19-6-12 (applied as a top-
dressing): 1, 4, 7, 10, 13, 16, 19, and 22 g/6 inch pot. The recommended rate for
dieffenbachias under these conditions is about 4 g (6). Plants height, number of
leaves and leachate soluble salts [using the pour-through method (7)] were recorded
'Professor of Plant Pathology, Central Florida Research and Education Center -
Apopka, 2807 Binion Road, Apopka, FL 32703.
at the beginning of each trial and again just prior to inoculation (about 8 weeks after
fertilization). Plant quality was also recorded after 8 weeks on the following scale:
1 (dead), 2 (poor, unsalable), 3 (marginal, salable), 4 (good, salable), and 5
Inoculation. One day prior to inoculation, plants were subjected to
intermittent misting (15 sec/30 min for 12 hr/day). They were then inoculated by
spraying with a suspension of the pathogen (X. campestris pv. dieffenbachiae 1 x 108
cells/ml) onto leaf surfaces with a pump action hand sprayer and immediately
covering with a plastic bag for 24 hours. The percentage of the leaf area with
symptoms of Xanthomonas blight was recorded about 3 weeks after inoculation.
Leachate soluble salts increased as fertilizer rate increased and ranged from
500 to 6500 mhos/cm. Increasing the Osmocote rate also affected height, number
of leaves and plant quality of Camille. Rates between 4 and 13 g Osmocote gave the
best growth although higher rates of fertilizer reduced height, leaf number and plant
quality only slightly (Fig. 1 3). Only plants receiving the lowest rate of fertilizer (1
g) showed substantially reduced growth.
The percentage of the leaf area with Xanthomonas blight decreased in a
linear fashion as the rate of Osmocote increased (Fig. 4). Plants receiving 22 g
Osmocote had only 30% the level of disease as those fertilized with the 1 g rate.
These results are the same as those obtained for the majority of other ornamentals
tested for fertilizer affects on Xanthomonas diseases including ficus, ivy, schefflera,
Ideally, fertilizer levels which reduce disease significantly should not result in
plant damage, excessive costs (due to high rates), or significantly increased potential
for ground water contamination. Fertilizer levels which reduced Xanthomonas blight
of Dieffenbachia, by at least 50% (13 g), did not significantly reduce plant growth but
represent a three-fold increase in the recommended rate of fertilizer for this plant.
An additional consideration is that fertilizer rates used to decrease one disease do
not increase the potential for other diseases. Previous research on Dieffenbachia
showed that increased fertilizer levels resulted in increased severity of Myrothecium
leaf spot disease (4). It is therefore unlikely that increasing the rate of fertilizer
applied to Dieffenbachia to reduce Xanthomonas leaf spot would be beneficial in the
overall production of the plant.
1. Chase, A. R. 1989. Aliette 80WP and bacterial disease control Xanthomonas.
Foliage Digest 12(11)1-3.
2. Chase, A. R. 1987. Update on controlling three bacterial diseases of foliage
plants. Foliage Digest 9(8):1-2.
3. Chase, A. R. 1987. Effect of fertilizer rate on susceptibility of Syngonium
podophyllum 'White Butterfly' to Erwinia chrysanthemi and Xanthomonas
campestris. Foliage Digest 10(8):15-16.
4. Chase, A. R., and R. T. Poole. 1985. Host nutrition and severity of
Myrothecium leaf spot of Dieffenbachia maculata 'Perfection'. Scientia
5. Chase, A. R., and R. T. Poole. 1986. Effects of host nutrition on growth and
susceptibility of Anthurium scherzeranum to Xanthomonas leaf spot.
Nurserymens Digest 20(6):58-59.
6. Conover, C. A., and R. T. Poole. 1984. Light and fertilizer recommendations
for production of acclimatized foliage plants. Foliage Digest 7(8):1-6.
7. Wright, R. D. 1986. The pour-through nutrient extraction procedure.
Figure 1. Effect of Osmocote 19-6-12 rate on height of Dieffenbachia
maculata cv. Camille.
1 4 7
10 13 16
mnocote/6 inch pot
Figure 2. Effect of Osmocote 19-6-12 rate on number of leaves on
Dieffenbachia maculata cv. Camille.
1 4 7
g Osmocote/6 inch pot
Figure 3. Effect of Osmocote 19-6-12 rate on plant quality of
Dieffenbachia maculata cv. Camille. Plant quality was rated
on a scale from 1 (dead) to 5 (excellent, salable).
13 16 19 22
g Osmocote/6 inch pot
Figure 4. Effect of
Osmocote 19-6-12 rate on percent disease on
maculata cv. Camille caused by Xanthomonas
1 4 7 10 13 16 19 22
g Osmocote/6 inch pot