Effects of Light Level and Nitrogen Fertilization on Growth of Heart-leaf Philodendron Stock Plants and Severity of Red-Edge Disease

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University of Florida
Institute of Food and Agricultural Sciences
Central Florida Research and Education Center

A.R. Chase and R.T. Poole*
CFREC-Apopka Research Report RH-93-9

Abstract

Philodendron scandens oxycardium stock plants with red-edge disease, caused by Xanthomonas campestris pv. dieffenbachiae, were grown under 1500, 3500 or 5500 ft-c light intensity and fertilized with 19-6-12 Osmocote at 4, 8 or 12 g/6-inch pot/3-months. Two cutting crops were propagated from the stock plants in each of two experiments. Stock plant fertilization rate was more important than light intensity for subsequent growth and quality of cuttings. Best quality crops were grown from cuttings harvested from stock plants fertilized at 8 or 12 g/6-inch pot. Stock plants grown under 1500 ft-c had significantly lower levels of rededge disease compared to plants grown under 3500 or 5500 ft-c. Stock plant fertilization rate did not affect severity of red-edge disease on stock plants or plants grown from their cuttings.

Introduction

Light and fertilizer levels for producing good quality acclimatized foliage plants have been published for most economically important species (6, 7). Less information is available on growth parameters for containerized stock plants grown in commercial type soilless media (5, 12). The following experiments were conducted to determine optimum light intensities and fertilizer levels for Philodendron scandens oxycardium (heart-leaf philodendron) container grown stock plants to produce high quality cuttings. The effects of light intensity and fertilizer level on severity of red-edge disease caused by the bacterium Xanthomonas campestris pv. dieffenbachiae were also evaluated.

Materials and Methods

Experiment 1. Research was initiated on February 28, 1991, when rooted heart-leaf philodendron cuttings, three per 3-inch pot, were repotted into 6-inch containers, using Vergro Container Mix A without superphosphate (Verlite Co., Tampa FL 33680). These stock plants were grown in a shadehouse in a 3 x 3 factorial experiment with 5 replications (pots) per treatment. Plants were arranged in a randomized block design under polypropylene shadecloth providing 45, 60 or 75% shade so that the maximum light intensity at plant level was 5500, 3500 or 1500 ft-c, respectively. Minimum and maximum air temperatures at bench level in the shadehouse during the course of the experiment were 65°F and 95°F, respectively.

Pots were top-dressed with 4, 8 or 12 g/6-inch pot 19-6-12 Osmocote (Grace/Sierra Co., Milpitas, CA 95053), on February 28 and again on May 21, 1991. Plants were watered overhead three times per week. Symptoms of red-edge disease (necrotic reddish-brown leaf margins) were first observed on foliage shortly after placement in the shadehouse. Naturally occurring infection by Xanthomonas campestris pv. dieffenbachiae, the bacterium causing rededge disease in philodendron, was confirmed by isolation of the pathogen.

Cuttings were harvested from stock plants on May 14 (crop la) and July 31, 1991 (crop lb). Stock vines were cut back to the pot rim during harvest. Cuttings were rooted by placing five single-eye nodes per 5-inch pot, in Vergro Container Mix A. Cuttings were placed under intermittent mist in a greenhouse where maximum light intensity at bench level was 2000 ft-c and temperatures ranged from 65°F to 95°F. Cuttings harvested on May 14 were removed from mist on June 25, those obtained on July 31 were removed on September 10, 1991. Cuttings were fertilized with 5 g/5-inch pot 19-6-12 Osmocote shortly before plants were moved to the shadehouse. After removal from mist, cuttings were placed under 1500 ft-c maximum light intensity in the same shadehouse as stock plants.

Total number of nodes on vines of stock plants was recorded when cuttings were harvested. Electrical conductivity (µmhos/cm) and pH of medium leachate from stock plants were measured on March 7 and June 28, 1991 using the pour through nutrient extraction procedure (13). Plant grade (based on a scale of 1 = dead, 2 = poor quality, unsalable, 3 = fair quality, salable, 4 = good quality and 5 = excellent quality) and total vine length were determined on August 9 (crop la) and on October 15, 1991 (crop lb). The severity of symptoms of red-edge disease on stock plants and plants grown from crop la cuttings were determined on June 14 and August 15, 1991, respectively.

Experiment 2. Experiment 2 began on October 15, l991, when cuttings were potted and placed under the same shade levels as in Experiment l. Containers were top-dressed on October 16, 1991 and again on January 29, 1992 with the same rates of 19-6-12 Osmocote as used in Experiment 1. Stock plants were graded based on the same scale as used in Experiment 1, on May 11, 1992. The pour-through method was used to determine electrical conductivity and pH of stock plant medium leachate on March 6 and May 15, 1992.

Two cutting crops were harvested and propagated under intermittent mist in the same manner as in Experiment 1. Crop 2a was harvested and propagated on January 10 and crop 2b on May 15, 1992. When adequately rooted (crop 2a on March 16, crop 2b on July 9, 1992) cuttings were placed under 60% shade in the shadehouse where stock plants were maintained. Both crops were fertilized with 5 g/5-inch pot 19-6-12 Osmocote on the day plants were moved to the shadehouse.

Plant grades, total vine length and number of nodes per vine on the 5-inch pots of heartleaf philodendron grown from cuttings were recorded on March 27 (crop 2a) or on August 14, 1992 (crop 2b). The number of leaves damaged by red-edge disease on stock plants and plants grown from cutting crops was determined on January 10, May 12 and August 13, 1992, respectively.

Results

Heart-leaf philodendron vines produced more nodes when grown under 1500 ft-c compared to plants grown in the two higher light intensities but fertilizer rate had no effect (Table 1). Total number of nodes per plant on crop lb heart-leaf philodendron plants harvested on July 30, however, was not affected by light intensity or fertilizer level (data not shown). Although crop 2a plants receiving the highest fertilizer rate were slightly shorter when compared to those grown at the lower rates, fertilizer rate did not significantly affect other growth parameters in either experiment (Table 1).

Plant grades from crop 1a and lb cuttings, as well as total length of vines from crop 1a cuttings, were not affected by light intensity (Table 2). Crop lb cuttings produced the longest vines when harvested from stock plants grown in the lowest light.

Fertilizer rate affected plant grade and vine length of plants grown from both la and lb cutting crops (Table 2). In general, plants grew more and received higher plant grades when either 8 or 12 g/6-inch pot rates of fertilizer were used.

Number of nodes per vine on plants grown from crop 2a cuttings was influenced by an interaction of light intensity and fertilizer rate on the stock plants (Figure 1). Plants with more nodes per vine were produced from stock plants grown under 60% shade (2500-3500 ft-c) receiving 12 g/6-inch pot of 19-6-12. As light intensity in stock plant area increased, more fertilizer was required to maintain the same node per vine ratio obtained with low light and low fertilizer.

As in Experiment l, one cutting crop (2a) was similarly affected by light intensity in stock plant areas, with longest vines grown from cuttings of stock plants under 75 % shade (5500 ft-c) (Table 3). Overall, plant grade of 2a cuttings was best when stock plants received 8 or 12 g/6-inch pot 19-6-12. Total vine length of both 2a and 2b crops and number of nodes on vines of 2b cuttings increased as fertilizer rate of stock plants increased.

Light intensity influenced severity of red-edge disease on heart-leaf philodendron stock plants in both experiments (Figure 2). Stock plants grown under the lower light level had significantly fewer leaves with symptoms of red-edge disease than those grown under the two higher light levels. In addition, there was a direct correlation between the severity of infection for stock plants and the severity of infection on the plants propagated from them. Severity of red-edge disease on either stock plants or plants grown from their cuttings was not influenced by fertilizer rate.

In a recent study Philodendron scandens oxycardium plants with leachate electrical conductivity measuring 1040 to 1460 µmhos/cm maintained their attractiveness when placed indoors for up to two months (11). The electrical conductivity measurements observed here for plants receiving 8 or 12 g/6-inch pot, 1050 and 1602 mhos/cm are close to that range.

Summary

Stock plant fertilization rate was more important than light intensity in the growth and quality of heart-leaf philodendron crops produced in these two experiments. Best quality crops were produced when stock plants received 8 or 12 g/6-inch pot rather than 4 g/6-inch pot of 19-6-12 Osmocote every 3 months.

Earlier research has shown that fertilizer rate can affect severity of bacterial disease infection of some foliage plants (2, 3, 4, 8). The fertilizer rates tested in these experiments were lower than those utilized when disease was evaluated in the above mentioned research and they did not influence disease severity on heart-leaf philodendron. Preinoculation light levels did not significantly influence bacterial disease expression on Syngonium podophyllum with Xanthomonas blight (1) or Schefflera arboricola with Pseudomonas leaf spot (3). However, light level was shown to affect severity of expression of Pseudomonas leaf spot on chrysanthemums (9) as well as red-edge disease in this report. Bactericides alone have so far provided very limited control of most bacterial diseases (10). Effective control is obtained with use of integrated disease control programs based on use of pathogen free plant material, proper sanitation practices and bactericides when needed. In the future, environmental manipulation should become an important part of integrated disease control programs.

*Professor of Plant Pathology and Professor of Plant Physiology, respectively, Central Florida Research and Education Center, 2807 Binion Road, Apopka, FL 32703-8504.

References

1. 1. Chase, A.R. 1988. Effects of temperature and preinoculation light level on severity of Syngonium blight caused by Xanthomonas campestris. J. Environ. Hortic. 6(2):61-63.
   2. Chase, A.R. 1989. Effect of nitrogen and potassium fertilizer rates on severity of xanthomonas blight of Syngonium podophyllum. Plant Disease 73:972-975.
   3. Chase, A.R. and J.B. Jones. 1986. Effects of host nutrition, leaf age, and preinoculation light levels on severity of leaf spot of dwarf schefflera caused by Pseudomonas cichorii Plant Disease 70:561-563
   4. Chase, A.R. and R.T. Poole. 1987. Effects of fertilizer rate on severity of xanthomonas leaf spot of schefflera and dwarf schefflera. Plant Disease 71:527-529.
   5. Conover, C.A. and R.T. Poole. 1972. Influence of shade and nutritional levels on growth and yield of Scindapsus aureus, Cordyline terminalis 'Baby Doll' and Dieffenbachia exotica. Proc. Trop. Reg. Amer. Soc. Hot. Sc. 16:227-281.
   6. Conover, C.A. and R.T. Poole. 1974. Influence of shade and fertilizer source and level on growth, quality and foliar content of Philodendron oxycardium Scott. J. Amer. Soc.Hort. Sc.. 99(2):150:152.
   7. Conover, C.A. and R.T. Poole. 1990. Light and fertilizer recommendations for the production of acclimatized potted foliage plants. Nursery Digest 24(10):34-36, 58-59.
   8. Harkness, R.W. and R.B. Marlatt. 1970. Effect of nitrogen, phosphorus and potassium on growth and xanthomonas disease of Philodendron oxycardium. J. Amer. Soc. Hort.Sci. 95:37-41.
   9. Jones, J.B., A.R. Chase, B.K. Harbaugh and B.C. Raju. 1985. Effect of leaf wetness, fertilizer rate, leaf age, and light intensity before inoculation on bacterial leaf spot of chrysanthemum. Plant Disease 69:782-784.
   10. Knauss, J.F., W.E. Waters and R.T. Poole. 1971. The evaluation of bactericides and bactericide combinations for the control of bacterial leaf spot and tipburn of Philodendron oxycardium incited by Xanthomonas dieffenbachiae. Proc. Fla. State Hot. Soc. 84:424428.
   11. Poole, R.T. and C.A. Conover. 1990. Leachate conductivity and pH for ten foliage plants. J. Environ. Hot. 8(4):166-172.
   12. Reyes, T., A.R. Chase and R.T. Poole. 1990. Effect of nitrogen level and light intensity on growth of Epipremnum aureum. Proc. Fla. State Hot. Soc. 103: 176-178.
   13. Wright, R.D. 1986. The pour-through nutrient extraction procedure. HortScience 21(2):227-229.

^zStock plants (three rooted cuttings per 6-inch pot) were started on February 28 and cutting crop 1a harvested on May 14, 1991. Crop 2a, harvested on January 10, 1992, was obtained from stock plants started on October 15, 1991.
^yPlants were graded on a scale of 1 = dead, 2 = poor quality, unsalable, 3 = fair quality, salable, 4 = good quality and 5 = excellent quality.
^xns, *,**; Results nonsignificant, significant at P = 0.05 and significant at P = 0.01, respectively.
^wPlants received 19-6-12 Osmocote at the rates indicated on February 28 and June 25 1991, in experiment 1 and on October 16, 1991 and January 29, 1992 in experiment 2.

^zPlant were graded using a scale of 1 = dead, 2 = poor quality, unsalable, 3 = fair quality, salable, 4 = good quality and 5 = excellent quality.
^yns, **; Results nonsignificant and significant at P = 0.01, respectively.
^xStock plants received 19-6-12 Osmocote at the rates indicated on February 28 and June 25 1991.

^zPlants were graded on a scale of I = dead, 2 = poor quality, unsalable, 3 = fair quality, salable, 4 = good quality and 5 = excellent quality.
^yns, *, **; Results nonsignificant, significant at P = 0.05 and significant at P = 0.01, respectively.
^xStock plants received 19-6-12 Osmocote at the rates indicated on October 16, 1991 and January 29, 1992.

Figure 1. Light and fertilizer levels in stock plant areas affect growth of heart-leaf philodendron cuttings.
Stock plants fertilized with Osmocote 19-6-12 at the rates indicated on Oct 16, 1991 and Jan 29, 1992.

Figure 2. Number of leaves with symptom of red-edge disease on heart-leaf philodendron stock plants and cuttings.
Damage rated for exp. 1 stock-Jun 14 and cuttings-Aug 2, 1991; for exp. 2 stock May 12 and cuttings-Aug 13, 1992.