Severity of Necrosis of Spathiphyllum 'Petite' Foliage Grown Under Various Air Temperatures, Fertilization Rates, and Irrigation Frequencies

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R. T. Poole and C. A. Conover*

University of Florida, IFAS
Central Florida Research and Education Center - Apopka
CFREC-Apopka Research Report, RH-90-18

Spathiphyllum 'Petite' (Petite or Bennett spathiphyllum) responds well to growth regulators, making it a suitable flowering foliage crop for 4 to 10-inch pot production. Since this is one of the more commonly grown cultivars of spathiphyllum readily controlled by growth regulators, Spathiphyllum 'Petite' has the potential to become more widely utilized by the foliage plant industry. Unfortunately, this spathiphyllum hybrid is much more-susceptible to necrosis of the leaf tips than less versatile cultivars. Florida growers have noticed 'Petite' tends to develop this condition much more readily during hot summer months, therefore some producers have limited production to the cooler season. The following research attempts to isolate the causal factors of 'Petite' tip necrosis and find ways to overcome this tendency.

This 4x3x2 factorial experiment with four replications was initiated on August 24, 1989, when liners of Spathiphyllum 'Petite' were placed in 6-inch plastic pots containing Vergro container mix (Canadian sphagnum peat moss, coarse grade vermiculite and perlite without superphosphate, Verlite Co., Tampa, FL 33680), amended with 1 lb. Micromax (Sierra Chemical Co., Milpitas, CA 95035) and 7 lbs. dolomite/yd³. Plants were grown in glasshouses where they received 1100 ft-c maximum light intensity, air temperature ranges of 59-82, 64-88, 70-93 or 75-99°F, and were watered once or twice weekly. On September 6, and again on December 18, 1989, plants were fertilized with 19-6-12 3-month release rate Osmocote (Sierra Chemical Co., Milpitas, CA 95035) at rates of 2, 4 or 6 g/6-inch pot. Height of test plants was recorded monthly, starting September 7, 1989, and ending March 13, 1990. Plant grade, and pH and micromhos/cm of the leachate, determined by the pour through nutrient extraction method, were recorded at the conclusion of the experiment in March 1990.

Air temperature, fertilization rate and irrigation frequency all interacted to create conditions favorable for tip necrosis development. Poorest quality plants having the most tip necrosis were produced with the highest temperature ranges and fertilizer rates tested, and watered only once a week (Table 1). Best quality 'Petite' plants having no tip necrosis were produced utilizing the more moderate temperature ranges, the highest fertilization rate tested, and watered twice a week.

Higher air temperatures, up to a point, cause plants to increase their photosynthesis and respiration rates. This increase in metabolic rate creates the potential for excess metabolites to collect in delicate new tissue forming at the growing tips of plants. Excess solute accumulation in developing tissues may cause the damage resulting in tip necrosis. Florida producers can predispose the plants to this problem in the summertime, when high air temperatures are unavoidable, by combining higher fertilization levels with infrequent watering schedules. As the growing medium dries its' soluble salts become more concentrated, especially in lightweight growing media, where a 50% loss in soil moisture approximately doubles the salts concentration. Soluble salts levels of the leachate from the media of pots growing 'Petite' were highest when plants received the higher temperature ranges and fertilization rates, and were watered only once a week (Table 2). This production regime also produced the lowest quality plant material having the most tip necrosis. Frequent waterings leach soluble salts from the growing media, hence fewer ions are incorporated into the transpiration stream, so tissue damage is less likely to occur.

Data recorded for height support these findings. Tallest plants were produced utilizing a temperature range of 70 to 93°F and watered twice a week, and also a temperature range of 59 to 82°F and watered once a week (Table 3).- The highest temperature regime tested, combined with only one watering per week produced the shortest plant material.

In analyzing the data collected from this test we can make some recommendations for growing Spathiphyllum 'Petite':

1. Install adequate ventilation for use during the hot summer months and make sure it is working properly. This will help keep the temperature within the recommended levels for foliage plant production. The recommended temperature range for spathiphyllums is 65 to 90°F.

2. Apply the recommended rate for the type of fertilizer used when growing spathiphyllum species. Example: When using 19-6-12 3-month release rate fertilizer, and spathiphyllum are growing in 6-inch pots, the recommended fertilization rate is 4.0 g/pot/3-months. These fertilization rate recommendations are listed in CFREC-A Research Report RH-90-1, Light and Fertilizer Recommendations for Production of Acclimatized Potted Foliage Plants.

3. Keep soil in pots moist during the hot Summer months by increasing irrigation frequency. When plants are grown under the recommended temperature and fertilization ranges, and soil is kept moist, no tip necrosis develops.

4. Soluble salts levels should be closely monitored when they are utilized as a factor in determining fertilizer application times and rates. Monthly testing will help individual producers establish a baseline to determine optimum soluble salts levels. Dangerously high salts concentrations can then be recognized early and media can be leached to remove excess ions before foliage damage occurs.

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

Additional Reading

1. Chase, A.R. and R.T. Poole. 1984. Severity of acephate phytotoxicity on Spathiphyllum Schott. cv. Clevelandii as influenced by host nutrition and temperature. J. Amer. Soc. Hort. Sci. 109(2):168-172.
2. Conover, C.A. and R.T. Poole. 1984. Light and fertilizer recommendations for production of acclimatized potted foliage plants. Agri. Res. Ctr.-Apopka AREC-A Res. Rpt. RH-84-7.
3. Hipp, B.W., P.F. Colbaugh and M. DiLeo. 1979. Influence of fertility and moisture level on growth of Chlorophytum. HortScience 14(1):65-66.
4. Joiner, J.N., C.A. Conover and R.T. Poole. 1981. Section of chapter on Nutrition and Fertilization in textbook, Foliage Plant Production, J.N. Joiner, University of Florida, Editor, Prentice-Hall, Englewood Cliffs, NJ pp.256-268.
5. Poole, R.T. 1981. Soluble salts interpretation. Foliage Digest 4(6):11-13.
6. Poole, R.T., C.A. Conover and A.R. Chase. 1985. Soluble salts interpretation for ornamental crop production. Proc. Trop. Reg. Amer. Soc. Hort. Sci. 27:33.
7. Wright, R.D. 1986. The pour-through nutrient extraction procedure. HortScience 21(2)227-229.

1. ^ZOsmocote 19-6-12 3-month release rate fertilizer surface applied September 6 and December 18, 1989.
   ^YPlants graded on a scale of 1 = poor quality, unsalable, 3 = fair quality, salable and 5 = excellent quality plant material.
   

1. ^ZResults significant at the 0.01% level.
   ^YOsmocote 19-6-12 3-month release rate fertilizer surface applied September 6, and December 18, 1989.
   ^XSoluble salts of the leachate were measured using the pour-through method.

^ZResults significant at the 0.01% level.