EFFECTS OF LEVELS OF PHOSPHORUS AND POTASSIUM

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1 POOLE AND SHEEHAN: CATTLEYA ORCHIDS 465 Concentrations and timing of applications used for disbudding appeared more critical than for pinching. High concentrations of both chemi cals disbudded and caused a second pinch, pro ducing plants with larger numbers of flowers compared to controls. Plants apparently were more sensitive to spray applications on the 17th short day than on 14th since secondary pinching increased, total bud number decreased and per cent disbudding increased. These compounds re portedly effect rapidly elongating cells more than on dividing ones. On the 17th short day cells were probably undergoing more rapid cell elonga tion than on the 14th short day and thus had greater sensitivity. Apical flower buds are in itiated sooner and cease rapid cell elongation sooner than laterals, therefore, applying these materials at a date later than the 17th short day would be expected to reduce secondary pinching and kill lateral buds undergoing rapid cell elongations. Experiments were conducted at temperatures in the greenhouse that often exceeded 100 F. At such temperatures chrysanthemum flowers can be distorted and tend to vary widely in maturation time. For this reason data on flower size and time an anthesis were not taken. Gen erally, flower size and time to anthesis appeared not affected by treatment, however, precise con clusions cannot be drawn due to lack of data in this area. BIBLIOGRAPHY 1. Cathey, H. M., G. L. Steffens, N. W. Stuart, and R. H. Zimmerman Chemical pruning of plants Science 153: Cathy, H. MA. H. Yoeman, and F. F. Smith Abortion of flower buds in Chrysanthemum after applica tion of selected petroleum fractions of high aromatic con tent. Hort. Sci. 1: ,«-fumta, T" L. Pyeatt, E. Conklin, and J. Yoshihashi Environmental conditions and effectiveness of chemical pinching agents on Azaleas. Florist's Review 142(3690): Joiner, J N., and T. J. Sheehan Morphological and biochemical effects of growth regulators on flowering plants. A. R. Fla. Agric. Exp. Stats p a- u*ji^ofranfk'i.a* M" and R' A- Crilev Chemical disbudding of chrysanthemums. Grower 67: a 6- McDowell, T Chemical pinching. Ohio Flor. Ass. Bull. No. 455 pp McDowell, Theodore C Tip pruning of orna mental plants. Ohio Agric. Exp. Stats. Res. Summ. 31: 23. EFFECTS OF LEVELS OF PHOSPHORUS AND POTASSIUM ON GROWTH, COMPOSITION AND INCIDENCE OF LEAF-TIP DIE-BACK IN CATTLEYA ORCHIDS H. A. Poole and T. J. Sheehan University of Florida Gainesville Abstract A 3x3x3 factorial experiment using a complete randomized block design was initiated on Janu ary 10, 1970 to determine effects of 3 levels each of P and K and 3 frequencies of application on growth and tissue analysis of Cattleya. Mericloned plants of Blc. Llewellyn x Lc Waianae were used with treatments replicated three times and a single plant constituted the experimntal unit. Increased leaf number was influenced by P and K levels, percent dry weight of N in roots varied with P and K levels and increasing o77o. A8riculture Experiment Station Journal Series P and K levels decreased leaf Ca. Tip die back appeared in 5 months at high P level. Introduction Orchids are widely cultivated throughout the world but very little information is available on their nutritional requirements. Past investiga tors have generally investigated effects on growth due to absence of single nutrient element. The naturally slow growth of orchids, re serves within pseudo-bulbs, and organic medium on which they are grown combine to make pro duction of deficiency symptoms difficult to deter mine in a short-term experiment. Deficiency symptoms of N, P and K are uncommon under good cultural practices, but a leaf die-back on new growth occurred in the University of Florida orchid collection and appeared to be a nutritional disorder. Among growers, this disorder has been

2 466 FLORIDA STATE HORTICULTURAL SOCIETY, 1970 blamed on dry conditions, high N fertilization andor sunburn. This experiment determined the cause as calcium deficiency. Evers and Laurie (4) demonstrated that added nutrients benefited orchids, especially growth of unflowered seedlings. Eversole (7) studied several modified nutrient solutions and concluded that a wide range of nutrient combina tions could be utilized advantageously by orchids. Withner and Van Camp (8) found that un fertilized Cattleya plants in osmunda differed little in tissue analysis from similar plants grown in haydite and fertilized twice a week with onehalf Wagner and Poesch (W.P.) nutrient solu tion. Analyses of common organic media (7) indicate that most plant nutrients needed by orchids can be supplied by the slow decomposi tion of orchid media. Davidson (3) investigated nutrient balance in Cattleya and found that deficiency symptoms were slow to develop. Chin (1) found that omission of K, P, Mg or Ca severely affected dry weights of Dendrobium phalaenopsis hybrids, but the leaves dropped before deficiency symptoms appeared. The most thorough work in orchid nutrition has been by Cibes, Childers sand Loustalot (2) on Vanilla. They found the best nutrient source to be a deep layer of mulch maintained over and around roots. In gravel culture, N deficiency occurred within three weeks, P de ficiency in three months followed by K deficiency several weeks later. Methods and Materials A 3x3x3 factorial experiment using a com plete randomized block design was initiated on January 10, 1970 to determine effects of three levels each of P and K and three frequencies of application on growth and inorganic tissue an alysis of Cattleya. Mericloned plants of Blc. Llewellyn x Lc. Waianae were potted in threeinch clay orchid pots four weeks prior to initia tion of fertilizer treatments in a commercial mix ture of tree fern fiber and redwood chips. The experiment was replicated three times with a single plant as an experimental unit. P was applied at rates of 0, 50 and 100 ppmapplication from phosphoric acid and K was applied at the same rates from potassium hydroxide. Treatments were applied at one, two and three week intervals and N was added with treatments at the rate of 100 ppmweek using ammonium nitrate. All plants received 50 ml. of nutrient solution or an equivalent amount of water weekly and watered between applications with tap water when needed. No additional nutrients were applied other than those in the growing medium and city water supply and solutions were not buffered for ph control. Plants were grown in a 50% shade, glass greenhouse. The experiment was terminated July 14, 1970 after symptoms of leaf die-back had developed. Plants were divided into leaves plus pseudobulbs and roots plus rhizome, dry weight determined and tissue analyzed for N, P, K, Ca, Mg, Ft, Mn, Zn, and Cu. Plants were also checked for in creases in number of roots, leaves, pseudobulbs and new leads as well as total leaf number dur ing the six-month period. Information on in cidence of die-back was also noted. Data were statistically analyzed using analysis of variance and treatment comparisons made by orthogonal single degrees of freedom procedure. Results and Discussion No attempt was made to buffer nutrient solu tions since little knowledge is available concern ing effects of buffering agents and additional salts on orchid growth. Influences due to increas ing P levels might, therefore be attributed to decreasing ph (Figure 1). Further experiments are needed to separate effects of ths two factors in orchid nutrition. Increase in leaf number (al) (Figure 2) was influenced by a PQ x KQ interaction AL tended to increase with application of either P or K but decreased when K : P was applied in a 1:1 ratio. A 2:1 or 1:2 ratio gave the greatest increase in leaf number. Increase in number of pseudobulbs and new growth (AG) (Figure 3) was influenced by a PL x KL interaction. Apply ing either K or P decreased AG. Depriving plants of K at low P levels produced more new leads but they failed to fully mature into leaves. P levels had no effect on AG at high K levels. Percent dry weight of root N (Figure 4) was affected by a PQ x KQ interaction. This was probably due to the use of NH4N03 as the N source. Increasing phosphate levels tended to increase NH4 ion absorption at lower K levels but at the high level, K exerted an antagonistic effect upon NH4 absorption which was not de pendent upon P levels. Percent dry weight of leaf (Figure 5) was influenced by a PL x KL interaction. Increasing

3 POOLE AND SHEEHAN: CATTLEYA ORCHIDS o 4.. P levels, ppmapplication Figure 3. Pt x Kl* interaction effects on the increase of new leads and pseudobulbs by Blc. Llwellyn x Lc. Waianae plants. *Significant at 5% level 50 IOC e.. u P levels, ppm Figure 1. Average ph of solutions at various levels of P. K levels increased percent K in leaves but high P levels decreased this effect probably because of H antagonism due to P source. A PL x KL interaction affected percent Ca in leaf tissue (Figure 6). In the absence of P, increasing K levels reduced Ca content, however, increasing P levels greatly reduced Ca content 1.9« l J. - 1 P levels, ppmapplication Figure 4. Pq x Kq* interaction'effects on per cent dry weight of N of roots in plants of Blc. Llwellyn x Lc. Waianae. *Significant at 5% level P levels, ppmapplication P levels, ppinapplicatxon, Figure 2. Pq x Kg* interaction effects on numbers of leaves produced by Blc. Llwellyn x Lc. Waianae plants. * Significant at 5% level Figure 5. Pj, x KQ* interaction effects on per cent dry weight of leaf tissue K in plants of Blc. Llwellyn x Lc. Waianae plants. * Significant at 5% level

4 468 FLORIDA STATE HORTICULTURAL SOCIETY, P levels, ppuiapplication Figure 6. Pl x Kl* interaction effects on per cent Ca in leaves of Blc. Llwellyn x Lc. Waianae plants Significant at 5% level at all K levels. The low ph of the nutrient solu tion could have affected microbial decomposition of the medium which had a Ca content of % dry weight. Hydrogen ion antagonism could also have decreased Ca absorption. Fre quency of application (Figure 7) also affected Ca contents. Weekly fertilization treatments probably had lowest Ca level due to more fre quent antagonism with H and K levels, and fewer applications of tap-water where ionic an tagonism did not prevent absorption from the medium and water supply. Plants receiving 100 ppm P every week de veloped symptoms of leaf die-back after 5 months of treatment and no other treatment developed these symptoms. Symptoms occurred on newly matured leaves as a darkening of veins approxi mately 1 cm. from the tip, later developing into a dark sunken spot which then spread to cover 3-4 cm, of leaf tip. There was a clear line of demarcation between healthy and dry, necrotic tissue (Figure 8). Die-back was rapid on new orchid leads with necrosis occurring on tips of leaves and usually causing death to leaf andor growing tip as the necrosis spread. Tip burn of young expanding leaves of azalea plants (6) was related to calcium deficiency and symptom of orchid leaf die-back are similar. Plants at the onset of the experiment averaged 1.4% Ca while plants showing leaf die-back ranged from 0.4 to 0.7% Ca at experiment ter mination. These symptoms differed from Ca de ficiency symptoms of other plant species in that there was a sharp change from necrotic to healthy tissue in Cattleya leaves rather than a region of chlorosis separating healthy and necrotic tissue. Davidson (3) worked with Cattleya and Chin (1) with Dendrobium phalaenopsis and described Ca deficiency as a reduc tion in growth and dry weight. Mott (5) developed similar necrotic symp toms on Cattleya plants growing in osmunda and related leaf tip burn on current year's growth to frequency, of watering and fertiliza tion. His work indicated that plants fertilized and watered every 5 days or constantly sitting in water showed die-back symptoms. Fertilized plants receiving water every fifth day may not absorb sufficient Ca as would plants with more frequent watering. A poor root system, as those sitting in water, might absorb sufficient N, P and K for active growth but insufficient amounts of Ca. 1.2 Fertilization Frequency, Weeks Figure 7. Main*effects of frequency of nutrient applications on leaf Ca content of Blc. Llwellyn x Lc. Waianae plants. * Significant at 1% level Figure 8. Blc. Llwellyn ffl Lc. Waianae Sunset plant showing typical leaf-tip dieback symptom on new growth.

5 POE: CHRYSANTHEMUM FLOWERS 469 Mott had insufficient controls and factorial combinations to clearly explain this phenomenon, however, effects of such factors as watering fre quency, condition of the medium and degree of root activity are not too dissimilar from findings of this experiment concerning Ca availability and absorption and their effects on leaf tip die-back. LITERATURE CITED 1. Chin, T. T Effect of major nutrient deficiencies in Dendrobium phalaenopsis hybrids. Am. Orchid Soc. Bull. 35: Cibes, H. R., N. F. Childers and A. J. Loustalot Influence of mineral deficiencies on growth and com position of Vanilla vines. PI. Physiol. 22: Davidson, O. W It pays to fertilize orchids. Am. Orchid Soc. Bull. 21: Evers, O. A. & Laurie Nutritional studies with orchids. Bimo. Bull Ohio Agr. Expt. Sta. 25: Mott, R. C Lack of water a cause of Cattleya leaf "die-back". Am. Orchid Soc. Bull. 25: Twigg, M. C. and C. B. Link Nutrient defici ency symptoms and leaf analysis of azaleas grown in sand culture. Proc. Amer. Soc. Hort. Sci. 57: Withner, C. L The Orchids, A Scientilc Survey. Ronald Press Co., N. Y. p Withner, C. L. & J. Van Camp Orchid leaf analyses Am. Orchid Soc. Bull. 17: EVALUATIONS OF PESTICIDES FOR PHYTOTOXICITY ON CHRYSANTHEMUM FLOWERS S. L. Poe Gulf Coast Experiment Station Bradenton Abstract Chemical insecticides and miticides were sprayed on several cultivars of chrysanthemum flowers to determine phytotoxicity. Low rates of several materials were safe but only Phosvel and Azodrin were safe at higher concentrations (4.0 and 1.5 aihg respectively). Galecron (1.0 aihg) did not injure flowers but caused a slight mar ginal chlorosis of leaves. Introduction Late season infestations of pest populations on chrysanthemums can cause severe damage and reduced flower quality. Common pests during this preharvest period include thrips, aphids and spider mites. Thrips and spider mite feeding produces brown streaks on petals, deformed blossoms and an irreversible wilt of petals. In addition spider mites leave an unattractive en tanglement of webbing as they crawl about over blossoms. Chemicals regularly applied to control these pests during the growing period often are unsuitable for use on open flowers. Dicofol and Florida Agricultural Experiment Stations Journal Series No ltrademark names are designated (R). Use of chemi cals in this paper does not mean endorsement of that product or the company producing the product. endosulfan have been used against flower pests and are safe but ineffective against resistant pest populations. Granular systemic materials applied to the soil often have disagreeable odors when used in closed areas, possess high mamalian toxicity or are unsightly in pots. Materials that have been effectively and safely used previously include phorate and disulfoton as granular systemics on potted greenhouse plants (4). Baranowski (1) found that TemikR1 provided good mite control systemically for long periods without phytotoxi city. Engelhard (2) reported that Meta-Systox-R sprayed on plants under a spectrum of conditions was phytotoxic. The use of methomyl and dieldrin in combination with fungicides some times resulted in injury to flowers or foliage (3), but these materials are not generally effective aphicides or miticides. Consequently, evaluations of new chemical materials for phytotoxicity on flowers were made during the spring and sum mer, The results are reported here. Materials and Methods Two tests were conducted using pot plants grown on raised benches in a greenhouse. Plots consisted of one pot each of several cultivars in bloom. Three applications of each chemical were made seven days apart with a hand sprayer; phytotoxicity evaluations were made visually prior to the first two applications and seven days after the final application. Materials, rates, formulations, dates of application and varieties