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L-3 Effect of Nutrition on Growth of Aphelandra square osa
and Severity of Myrothecium Leaf Spot Central Sci(
A. R. Chase and R. T. Poole ibrr
University of Florida, IFAS OCT 14
Agricultural Research and Education Center Apcpka
AREC-Apopka Research Report RH-86-3
Myrothecium leaf spot is a serious disease of many foliage plants
including Aphelandra squarrosa (Zebra plant). Symptoms are most commonly
confined to large (1/2 inch wide) lesions on lower leaves which have been
wounded or are in contact with the potting medium or the edge of the pot
(1). The pathogen, Myrothecium roridum, shows no host specificity with a
single isolate causing disease on most susceptible plants (3). Many tests
performed with dieffenbachias have shown that the optimum temperature range
for development of Myrothecium leaf spot is between 70 and 85F with little
disease occurring during the summer when temperatures are frequently over
90F (2). In addition, nutritional tests on Myrothecium leaf spot of
dieffenbachias have shown that over-fertilized plants develop more lesions
than under-fertilized or correctly fertilized plants (4). The test
described in this report was conducted to evaluate the effect of fertilizer
level on growth of Zebra plant and its susceptibility to Myrothecium leaf
Liners of Zebra plant 'Dania' were obtained from a commercial producer
and planted in 5" pots containing a steam-treated medium consisting of 50%
Canadian peat and 50% pine back. The medium was amended with 7 Ibs
dolomite and 1 lb Micromax/yd after steaming at 190*F for 1.5 hr. After
1 week, ten plants each were top-dressed with one.of the following rates of
Osmocote 19-6-12: 0.5, 2.0, 3.5, 5.0, 6.5, 8.0, 9.5, and 11.0 g/pot. The
recommended rate for this plant for a 3 month period is 2.1 g Osmocote
19-6-12/5" pot (5). Plant height, number of leaves, and soluble salts of
the potting medium were determined monthly (using the leachate method)
starting the week fertilizer was applied until 8 weeks later. Plants were
wounded with a sterile dissecting needle V8 wounds/plant), sprayed with a
conidial suspension of M. roridum (1 x 10 conidia/ml) just to runoff, and
placed in a polyethylene bag for 1 week. The number of lesions which
formed at wound sites was then recorded.
Fertilizer treatment did not affect number of leaves produced by the
plant, although both plant height and quality were affected significantly
(Table 1). Plant height and quality reacted very much the same to
fertilizer treatment with best plants produced at levels between
Associate Professor of Plant Pathology and Professor of Ornamental
Horticulture, University of Florida, IFAS, AREC-Apopka, 2807 Binion Rd.,
Apopka, FL 32703.
2.0 and 6.5 g/pot. Rates above or below this range produced shorter,
poorer quality plants. This fertilizer range corresponded to a soluble
salts range from about 2500 to 6600 mhos/cm. Plants fertilized at the
lowest level showed signs of chlorosis. During the winter months, the
recommended rate of fertilizer (2.1 g) may be a little low, since plants
fertilized with 3.5 g were of slightly better quality than those fertilized
with lower rates. Fewest lesions formed on plants receiving the lowest
fertilizer treatment with most lesions on plants in the highest treatment.
Plants in other treatments had intermediate numbers of lesions which
differed little from each other. This response, most clearly shown on
dieffenbachias (4), may hold true for other foliage plants susceptible to
Myrothecium leaf spot.
1. Chase, A. R. 1981. Comparison of Myrothecium sp. and Corynespora
cassiicola leafspots on two cultivars of Aphelandra squarrosa Nees.
Proc. Fla. State Hort. Soc. 94:115-116.
2. Chase, A. R. 1983. Influence of host plant and isolate source on
severity of Myrothecium leaf spot of foliage plants. Plant Disease
3. Chase, A. R., and R. T. Poole. 1984. Influence of temperature on
severity of Myrothecium leaf spot of Dieffenbachia maculata
'Perfection'. Plant Disease 68:488-490.
4. Chase, A. R., and R. T. Poole. 1985. Host nutrition and severity of
Myrothecium leaf spot of Dieffenbachia maculata 'Perfection'. Scientia
5. Conover, C. A., and R. T. Poole. 1984. Light and fertilizer
recommendations for production of acclimatized potted foliage plants.
Foliage Digest 7(8):1-6.
Table 1. Effect of host nutrition on growth of Aphelandra squarrosa and its
susceptibility to Myrothecium roridum.
5" pot Plant No. Plant No. Soluble salts
(g) ht.(in) leaves quality lesions (jmhos/cm)
0.5 3.3*y 13.5ns 3.1** 0.7ns 144**
2.0 3.7 15.1 3.7 2.0 2564
3.5 3.9 15.4 4.0 1.4 3952
5.0 3.6 15.3 4.0 1.8 4062
6.5 3.7 15.9 4.0 2.1 6625
8.0 3.4 15.5 3.5 2.1 7772
9.5 3.2 15.6 3.6 1.8 9168
11.0 3.5 15.2 3.4 2.7 7970
ZQuality was rated on the following scale: 1 = dead; 3 = good, salable;
5 = excellent, very salable.
YSignificance of the analysis of variance was denoted as ns(not
significant), *(significant at 5%), or **(significant at 1%).