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Effect of growth inhibitors on three ornamental species
Scientia Horticulturae, 9 (1978) 279--283
279
Elsevier Scientific Publishing Company, Amsterdam - - Printed in The Netherlands
EFFECT OF GROWTH INHIBITORS ON THREE ORNAMENTAL SPECIES
MICHAEL A. COHEN
Department of Horticulture, North Carolina State University, Raleigh, North Carolina
(U.S.A.) (First received 9 November 1977; in revised form 6 March 1978)
ABSTRACT Cohen, M.A., 1978. Effect of growth inhibitors on three ornamental species. Scientia Hortic., 9: 279--283. Foliar sprays of the growth inhibitors sodium 2, 3:4, 6-di-O-isopropylidine-a L-xylo-2hexulofuranosonate (dikegulac-sodium), N- [ 2,4-dimethyl-5- ] [(tri-fluromethyl) sulfonyl ] amino] phenyl] acetamide (mefluidide); methyl-2-chloro-9-hydroxyfluorene-9-carboxylate (chlorflurenol) and 2,3 dihydro-5-6-diphenyl-l,4-oxathiin (UBI-P293)were applied to Ligustrum japonicum, Pyracantha coccinea and Osmanthus heterophylla. Results indicate that growth inhibitors differ in their capacity to inhibit vegetative growth, and the level of inhibition and plant p h y t o t o x i c i t y depend on both the chemical and the rate of concentration.
INTRODUCTION
Use of growth inhibitors to reduce maintenance cost of woody ornamentals on highways, industrial and city parks, and on rights-of-way in large metropolitan areas has had limited commercial success. Lack of usage of inhibitors by contractors and city arborists has been due primarily to (1) lack of effectiveness on major plant genera, (2) undesirable plant growth habit after initial outgrowth, (3) phytotoxicity, and (4) unfavorable effect on flowering and fruit set. Studies by Sachs et al. (1970, 1975a) and Sachs and Hackett (1972) indicated maleic hydrazide and chlorflurenolmethyl are effective stem inhibitors on a number of species, but adversely affect plant appearance. Sachs and Maire (1967) reported on the importance of species susceptibility, material penetration, and inactivation and duration of inhibitors in relationship to vegetative growth of woody ornamentals. Sachs et al. (1975b) reported that several surfactants in conjunction with maleic hydrazide inhibited stem elongation on such genera as Pinus radiata, Viburnum ]aponicum, Juniperus sabina 'Tamariscifolia', and Pyracantha coccinea. Sanderson (1973), Asher (1963), Cathey and Stuart (1961) and Pharis et al. (1967) have reported that such compounds as Amo-1618, succinic acid
280
2,2 dimethylhydrazide, chlormequat chloride, dikegulac, and dichlorobenzylphosphonium chloride inhibited stem growth in a number of species. The present study was conducted to evaluate 4 growth inhibitors on 3 plant species which are commonly used in the landscape and require considerable manpower to maintain them. METHODS AND MATERIALS Two-year-old established container grown plants of Ligustrum japonicum, Osmanthus heterophylla (used only in 1976) and newly transplanted liners of Pyracantha coccinea were selected on 1 May 1975 and 26 May 1976. Ligustrum and Osmanthus were pruned to several uniform stems per plant while Pyracantha plants were pruned to a uniform height. Treatments were arranged in a randomized complete block design, with each treatment replicated 3 times. On 8 May 1975 and 26 May 1976 plants were sprayed with the following chemicals to run-off and allowed to dry for 24 hours before irrigating: chlorflurenol, dikegulac-sodium, UBI-P293, and mefluidide. Spray treatments were applied with a CO2 pressurized sprayer at 25 psi. Temperature at time of application was 23 ° C in 1975 and 22 ° C in 1976. Criteria used to evaluate new vegetative growth of Ligustrum and Osmanthus consisted of removing all new shoots and foliage except the initially pruned stems. Growth of Pyracantha was determined by decapitating the plant at the crown. Data on combined dry weight of shoots and foliage, and plant appearance were recorded. Plant phytotoxicity was based on a scale of 1--5 with 3.5 considered commercially acceptable in plant appearance. RESULTS Dikegulac-sodium, chlorflurenol, and mefluidide inhibited vegetative growth of Ligustrum japonicum, while UBI-P293 was least effective (Table I). At rates tested, concentration of dikegulac-sodium, chlorflurenol, and mefluidide showed no significant difference. Plant injury due to chemical treatments indicate that greater differences in phytotoxicity existed between chemicals than were due to different concentrations of a given chemical. Injury symptoms related to chlorflurenol treatment on new foliage and shoots showed (1) shortening of internode length, (2) reduction in leaf size, and (3) epinastic appearance of foliage. These undesirable characteristics were temporary in nature with secondary flushes of growth showing normal foliage and shoot development. Plants treated with 2000 p.p.m, of dikegulac-sodium were severely stunted, while rates of 3000--6000 p.p.m, caused death of plants. Treatments of mefluidide and UBI-P293 showed no foliage distortion but dieback of shoots was noted. Mefluidide treated plants gave best results when plant appearance and inhibitory activity were evaluated. Dikegulac-sodium (3000--6000 p.p.m.) and chlorflurenol treatments re-
281
TABLE 1 Effect of dikegulac-sodium, mefluidide, chlorflurenol and UBI-P293 on inhibition of vegetative growth of Ligustrum after 6 (1975) and 9 (1976) weeks of treatment. Injury based on 1 = death of plant; 3.5 = commercially acceptable; 5.0 = no injury; 3 replications per treatment. Mean separation within column by Duncan's multiple test, 5% level. Treatment
Rate (p.p.m.)
Dry weight of new foliage and shoots (g) 1975
Dikegulac-sodium Dikegulac-sodium Dikegulac-sodium Dikegulac-sodium Dikegulac-sodium Chlorflurenol Chlorflurenol Mefluidide Mefluidide Mefluidide Mefluidide UBI-P293 UBI-P293 UBI-P293 UBI-P293 UBI-P293 Control
2000 3000 4000 5000 6000 240 480 960 1440 2400 3600 7500 10000 12500 15000 20000
1976
0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 6.5 a 6.5 a 7.5 a 0.0 a
6.5 a
16.5 a 15.0 a 52.5 bc 40.5 b 36.5 b 57.0 bc
Phytotoxicity
42.5 b 34.0 b 82.0 c
1.0 1.0 1.0 1.0 1.0 3.5 3.0 4.0 4.0 4.0 3.5 5.0 5.0 5.0 5.0 5.0 5.0
d u c e d s h o o t a n d foliage g r o w t h o f Pyracantha coccinea while mefluidide and U B I - P 2 9 3 were less effective (Table 2). Plants t r e a t e d with dikegulacs o d i u m s h o w e d a significant difference in r e d u c t i o n o f g r o w t h due to c o n c e n tration, while n o differences o c c u r r e d with chlorflurenol. T r e a t m e n t s o f dikegulac-sodium at 2 0 0 0 - - 6 0 0 0 p.p.m, s h o w e d n o adverse p l a n t affect, while c h l o r f l u r e n o l e x h i b i t e d epinastic g r o w t h . All chemicals r e d u c e d g r o w t h o f Osmanthus heterophylIa (Table 3). No p l a n t injury was n o t e d with a n y chemical. DISCUSSION
These studies s h o w t h a t certain g r o w t h inhibitors (within the c o n c e n t r a t i o n used) can r e d u c e g r o w t h o f w o o d y o r n a m e n t a l s . G r o w t h inhibitors differ in their c a p a c i t y t o inhibit vegetative g r o w t h a n d t o cause p h y t o t o x i c i t y t o certain p l a n t species. The level o f i n h i b i t i o n d e p e n d e d largely on t y p e o f comp o u n d as well as the rate. C a t h e y and S t u a r t ( 1 9 6 1 ) have r e p o r t e d t h a t g r o w t h inhibitors are p l a n t species specific and t h a t differences b e t w e e n genera, or species within genera, m a y be due t o differences in a b s o r p t i o n , t r a n s p o r t , or m e t a b o l i s m o f the c o m p o u n d within t h e plant. Sachs et al. ( 1 9 7 0 ) have s h o w n
282
TABLE 2 Effect o f dikegulac-sodium, mefluidide, c h l o r f l u r e n o l a n d U B I - P 2 9 3 o n i n h i b i t i o n o f vegetative g r o w t h o f Pyracantha a f t e r 6 ( 1 9 7 5 ) a n d 9 ( 1 9 7 6 ) weeks o f t r e a t m e n t . I n j u r y based o n 1 = d e a t h o f p l a n t ; 3.5 = c o m m e r c i a l l y a c c e p t a b l e ; 5.0 = n o i n j u r y ; 3 r e p l i c a t i o n s per t r e a t m e n t . Mean s e p a r a t i o n w i t h i n c o l u m n b y D u n c a n ' s m u l t i p l e test, 5% level. Treatment
Rate (p.p.m.)
Dry w e i g h t of n e w foliage and shoots
Phytotoxicity
(g) 1975 Dikegulac-sodium Dikegulac-sodium Dikegulac-sodium Dikegulac-sodium Dikegulac-sodium Chlorflurenol Chlorflurenol Mefluidide Mefluidide Mefluidide UBI-P293 UBI-P293 UBI-P293 UBI-P293 UBI-P293 Control
2000 3000 4000 5000 6000 240 480 960 1440 2400 7500 10000 12500 15000 20000
1976
25.5 b 19.5 a 14.0 a 20.5 a 12.5 a 14.0 a 14.5 a 31.0 b 34.5 b
14.5 a 17.0 a
48.5 b 23.5 b 21.5 b 29.0 b
32.0 b
24.0 a 26.2 a 74.0 b
4.5 4.5 4.5 4.5 4.5 3.0 3.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0
TABLE 3 E f f e c t of dikegulac-sodium, m e f l u i d i d e , c h l o r f l u r e n o l a n d U B I - P 2 9 3 o n i n h i b i t i o n of vegetative g r o w t h o f Osmanthus 9 weeks a f t e r t r e a t m e n t (1976). I n j u r y b a s e d o n 1 = d e a t h of p l a n t ; 3.5 ffi c o m m e r c i a l l y a c c e p t a b l e ; 5.0 = n o i n j u r y ; 3 r e p l i c a t i o n s p e r t r e a t m e n t . Mean s e p a r a t i o n w i t h i n c o l u m n b y D u n c a n ' s m u l t i p l e test, 5% level.
Treatment
Rate (p.p.m.)
Dry weight of new foliage and shoots
Phytotoxicity
(g) Dikegulac-sodium Dikegulac-sodium Chlorflurenol Chlorflurenol Mefluidide Mefluidide UBI-P293 UBI-P293 Control
3000 5000 240 480 2400 3600 15000 20000
26.5 a 16.5 a 18.5 a 15.0 a 14.5 a 14.5 a 14.5 a 15.2 a 37.2 b
5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0
283
that numerous tree species in the same climatic zone and similar stage of development showed marked differences in plant inhibition with the same concentration of maleic hydrazide. My results suggest that growth inhibitors are plant specific but that some inhibitors, such as dikegulac-sodium, can effectively reduce growth of a number of genera within a narrow concentration range. With this reduction of growth, only minor phytotoxicity resulted, except with Ligustrum. Cohen (1976) has reported that rates of 1000--5000 p.p.m, of dikegulac-sodium gave acceptable plant control with minor phytotoxicity to Ilex species, Rhododendron species, Kalmia species, Berberis species, and Juniperus species. Further investigations are required with dikegulac-sodium to define proper time of application, formulation, dosage and method of application (spray versus soil drench) before its large scale use can be recommended.
REFERENCES Asher, W.C., 1963. Effects of 2-chloroethyltrimethyl (ammonium chloride) and 2,4 dichlorobenzyltributyl phosphonium chloride on growth and transpiration of slash pine. Nature (London), 200: 912. Cathey, H.M. and Stuart, N.W., 1961. Comparative plant growth-retarding activity of Amo 1618, Phosfon, and CCC. Bot. Gaz., 123: 51--57. Cohen, M.A., 1976. Herbicides and growth regulators for ornamentals and Christmas trees. Hortic. Crops Res. Set. 36, Dept. of Hortic, N.C. State Univ., p. 76. Pharis, R.P., Ruddat, M. and Phillips, C., 1967. Response of conifers to growth retardents. Bot. Gaz., 128(2): 105--109. Sachs, R.M. and Hackett, W.P., 1972. Chemical inhibition of plant height. HortScience, 7: 440--447. Sachs, R.M. and Maire, R.G., 1967. Chemical control of growth and flowering of woody ornamentals. J. Am. Soc. Hortic. Sci., 91: 728--734. Sachs, R.M., Hackett, W.P., Maire, R., Kretchun, T. and DeBie, J., 1970. Chemical control of plant growth in landscapes. Calif. Agric. Exp. Stn. Bull., p. 844. Sachs, R.M., Hield, H. and DeBie, J., 1975a. Dikegulac: A promising new foliar-applied growth regulator for woody species. HortScience, 10: 367--369. Sachs, R.M., DeBie, D., Kretchun, T. and Mock, T., 1975b. Comparative activity of commercially available maleic hydrazide formulations on several plant species. HortScience, 10: 366--367. Sanderson, K.C., 1973. Screening chemicals for controlling growth and flowering of Forsythia intermedia 'Zabel'. HortScience, 8: 477--479.
279
Elsevier Scientific Publishing Company, Amsterdam - - Printed in The Netherlands
EFFECT OF GROWTH INHIBITORS ON THREE ORNAMENTAL SPECIES
MICHAEL A. COHEN
Department of Horticulture, North Carolina State University, Raleigh, North Carolina
(U.S.A.) (First received 9 November 1977; in revised form 6 March 1978)
ABSTRACT Cohen, M.A., 1978. Effect of growth inhibitors on three ornamental species. Scientia Hortic., 9: 279--283. Foliar sprays of the growth inhibitors sodium 2, 3:4, 6-di-O-isopropylidine-a L-xylo-2hexulofuranosonate (dikegulac-sodium), N- [ 2,4-dimethyl-5- ] [(tri-fluromethyl) sulfonyl ] amino] phenyl] acetamide (mefluidide); methyl-2-chloro-9-hydroxyfluorene-9-carboxylate (chlorflurenol) and 2,3 dihydro-5-6-diphenyl-l,4-oxathiin (UBI-P293)were applied to Ligustrum japonicum, Pyracantha coccinea and Osmanthus heterophylla. Results indicate that growth inhibitors differ in their capacity to inhibit vegetative growth, and the level of inhibition and plant p h y t o t o x i c i t y depend on both the chemical and the rate of concentration.
INTRODUCTION
Use of growth inhibitors to reduce maintenance cost of woody ornamentals on highways, industrial and city parks, and on rights-of-way in large metropolitan areas has had limited commercial success. Lack of usage of inhibitors by contractors and city arborists has been due primarily to (1) lack of effectiveness on major plant genera, (2) undesirable plant growth habit after initial outgrowth, (3) phytotoxicity, and (4) unfavorable effect on flowering and fruit set. Studies by Sachs et al. (1970, 1975a) and Sachs and Hackett (1972) indicated maleic hydrazide and chlorflurenolmethyl are effective stem inhibitors on a number of species, but adversely affect plant appearance. Sachs and Maire (1967) reported on the importance of species susceptibility, material penetration, and inactivation and duration of inhibitors in relationship to vegetative growth of woody ornamentals. Sachs et al. (1975b) reported that several surfactants in conjunction with maleic hydrazide inhibited stem elongation on such genera as Pinus radiata, Viburnum ]aponicum, Juniperus sabina 'Tamariscifolia', and Pyracantha coccinea. Sanderson (1973), Asher (1963), Cathey and Stuart (1961) and Pharis et al. (1967) have reported that such compounds as Amo-1618, succinic acid
280
2,2 dimethylhydrazide, chlormequat chloride, dikegulac, and dichlorobenzylphosphonium chloride inhibited stem growth in a number of species. The present study was conducted to evaluate 4 growth inhibitors on 3 plant species which are commonly used in the landscape and require considerable manpower to maintain them. METHODS AND MATERIALS Two-year-old established container grown plants of Ligustrum japonicum, Osmanthus heterophylla (used only in 1976) and newly transplanted liners of Pyracantha coccinea were selected on 1 May 1975 and 26 May 1976. Ligustrum and Osmanthus were pruned to several uniform stems per plant while Pyracantha plants were pruned to a uniform height. Treatments were arranged in a randomized complete block design, with each treatment replicated 3 times. On 8 May 1975 and 26 May 1976 plants were sprayed with the following chemicals to run-off and allowed to dry for 24 hours before irrigating: chlorflurenol, dikegulac-sodium, UBI-P293, and mefluidide. Spray treatments were applied with a CO2 pressurized sprayer at 25 psi. Temperature at time of application was 23 ° C in 1975 and 22 ° C in 1976. Criteria used to evaluate new vegetative growth of Ligustrum and Osmanthus consisted of removing all new shoots and foliage except the initially pruned stems. Growth of Pyracantha was determined by decapitating the plant at the crown. Data on combined dry weight of shoots and foliage, and plant appearance were recorded. Plant phytotoxicity was based on a scale of 1--5 with 3.5 considered commercially acceptable in plant appearance. RESULTS Dikegulac-sodium, chlorflurenol, and mefluidide inhibited vegetative growth of Ligustrum japonicum, while UBI-P293 was least effective (Table I). At rates tested, concentration of dikegulac-sodium, chlorflurenol, and mefluidide showed no significant difference. Plant injury due to chemical treatments indicate that greater differences in phytotoxicity existed between chemicals than were due to different concentrations of a given chemical. Injury symptoms related to chlorflurenol treatment on new foliage and shoots showed (1) shortening of internode length, (2) reduction in leaf size, and (3) epinastic appearance of foliage. These undesirable characteristics were temporary in nature with secondary flushes of growth showing normal foliage and shoot development. Plants treated with 2000 p.p.m, of dikegulac-sodium were severely stunted, while rates of 3000--6000 p.p.m, caused death of plants. Treatments of mefluidide and UBI-P293 showed no foliage distortion but dieback of shoots was noted. Mefluidide treated plants gave best results when plant appearance and inhibitory activity were evaluated. Dikegulac-sodium (3000--6000 p.p.m.) and chlorflurenol treatments re-
281
TABLE 1 Effect of dikegulac-sodium, mefluidide, chlorflurenol and UBI-P293 on inhibition of vegetative growth of Ligustrum after 6 (1975) and 9 (1976) weeks of treatment. Injury based on 1 = death of plant; 3.5 = commercially acceptable; 5.0 = no injury; 3 replications per treatment. Mean separation within column by Duncan's multiple test, 5% level. Treatment
Rate (p.p.m.)
Dry weight of new foliage and shoots (g) 1975
Dikegulac-sodium Dikegulac-sodium Dikegulac-sodium Dikegulac-sodium Dikegulac-sodium Chlorflurenol Chlorflurenol Mefluidide Mefluidide Mefluidide Mefluidide UBI-P293 UBI-P293 UBI-P293 UBI-P293 UBI-P293 Control
2000 3000 4000 5000 6000 240 480 960 1440 2400 3600 7500 10000 12500 15000 20000
1976
0.0 a 0.0 a 0.0 a 0.0 a 0.0 a 6.5 a 6.5 a 7.5 a 0.0 a
6.5 a
16.5 a 15.0 a 52.5 bc 40.5 b 36.5 b 57.0 bc
Phytotoxicity
42.5 b 34.0 b 82.0 c
1.0 1.0 1.0 1.0 1.0 3.5 3.0 4.0 4.0 4.0 3.5 5.0 5.0 5.0 5.0 5.0 5.0
d u c e d s h o o t a n d foliage g r o w t h o f Pyracantha coccinea while mefluidide and U B I - P 2 9 3 were less effective (Table 2). Plants t r e a t e d with dikegulacs o d i u m s h o w e d a significant difference in r e d u c t i o n o f g r o w t h due to c o n c e n tration, while n o differences o c c u r r e d with chlorflurenol. T r e a t m e n t s o f dikegulac-sodium at 2 0 0 0 - - 6 0 0 0 p.p.m, s h o w e d n o adverse p l a n t affect, while c h l o r f l u r e n o l e x h i b i t e d epinastic g r o w t h . All chemicals r e d u c e d g r o w t h o f Osmanthus heterophylIa (Table 3). No p l a n t injury was n o t e d with a n y chemical. DISCUSSION
These studies s h o w t h a t certain g r o w t h inhibitors (within the c o n c e n t r a t i o n used) can r e d u c e g r o w t h o f w o o d y o r n a m e n t a l s . G r o w t h inhibitors differ in their c a p a c i t y t o inhibit vegetative g r o w t h a n d t o cause p h y t o t o x i c i t y t o certain p l a n t species. The level o f i n h i b i t i o n d e p e n d e d largely on t y p e o f comp o u n d as well as the rate. C a t h e y and S t u a r t ( 1 9 6 1 ) have r e p o r t e d t h a t g r o w t h inhibitors are p l a n t species specific and t h a t differences b e t w e e n genera, or species within genera, m a y be due t o differences in a b s o r p t i o n , t r a n s p o r t , or m e t a b o l i s m o f the c o m p o u n d within t h e plant. Sachs et al. ( 1 9 7 0 ) have s h o w n
282
TABLE 2 Effect o f dikegulac-sodium, mefluidide, c h l o r f l u r e n o l a n d U B I - P 2 9 3 o n i n h i b i t i o n o f vegetative g r o w t h o f Pyracantha a f t e r 6 ( 1 9 7 5 ) a n d 9 ( 1 9 7 6 ) weeks o f t r e a t m e n t . I n j u r y based o n 1 = d e a t h o f p l a n t ; 3.5 = c o m m e r c i a l l y a c c e p t a b l e ; 5.0 = n o i n j u r y ; 3 r e p l i c a t i o n s per t r e a t m e n t . Mean s e p a r a t i o n w i t h i n c o l u m n b y D u n c a n ' s m u l t i p l e test, 5% level. Treatment
Rate (p.p.m.)
Dry w e i g h t of n e w foliage and shoots
Phytotoxicity
(g) 1975 Dikegulac-sodium Dikegulac-sodium Dikegulac-sodium Dikegulac-sodium Dikegulac-sodium Chlorflurenol Chlorflurenol Mefluidide Mefluidide Mefluidide UBI-P293 UBI-P293 UBI-P293 UBI-P293 UBI-P293 Control
2000 3000 4000 5000 6000 240 480 960 1440 2400 7500 10000 12500 15000 20000
1976
25.5 b 19.5 a 14.0 a 20.5 a 12.5 a 14.0 a 14.5 a 31.0 b 34.5 b
14.5 a 17.0 a
48.5 b 23.5 b 21.5 b 29.0 b
32.0 b
24.0 a 26.2 a 74.0 b
4.5 4.5 4.5 4.5 4.5 3.0 3.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0
TABLE 3 E f f e c t of dikegulac-sodium, m e f l u i d i d e , c h l o r f l u r e n o l a n d U B I - P 2 9 3 o n i n h i b i t i o n of vegetative g r o w t h o f Osmanthus 9 weeks a f t e r t r e a t m e n t (1976). I n j u r y b a s e d o n 1 = d e a t h of p l a n t ; 3.5 ffi c o m m e r c i a l l y a c c e p t a b l e ; 5.0 = n o i n j u r y ; 3 r e p l i c a t i o n s p e r t r e a t m e n t . Mean s e p a r a t i o n w i t h i n c o l u m n b y D u n c a n ' s m u l t i p l e test, 5% level.
Treatment
Rate (p.p.m.)
Dry weight of new foliage and shoots
Phytotoxicity
(g) Dikegulac-sodium Dikegulac-sodium Chlorflurenol Chlorflurenol Mefluidide Mefluidide UBI-P293 UBI-P293 Control
3000 5000 240 480 2400 3600 15000 20000
26.5 a 16.5 a 18.5 a 15.0 a 14.5 a 14.5 a 14.5 a 15.2 a 37.2 b
5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0 5.0
283
that numerous tree species in the same climatic zone and similar stage of development showed marked differences in plant inhibition with the same concentration of maleic hydrazide. My results suggest that growth inhibitors are plant specific but that some inhibitors, such as dikegulac-sodium, can effectively reduce growth of a number of genera within a narrow concentration range. With this reduction of growth, only minor phytotoxicity resulted, except with Ligustrum. Cohen (1976) has reported that rates of 1000--5000 p.p.m, of dikegulac-sodium gave acceptable plant control with minor phytotoxicity to Ilex species, Rhododendron species, Kalmia species, Berberis species, and Juniperus species. Further investigations are required with dikegulac-sodium to define proper time of application, formulation, dosage and method of application (spray versus soil drench) before its large scale use can be recommended.
REFERENCES Asher, W.C., 1963. Effects of 2-chloroethyltrimethyl (ammonium chloride) and 2,4 dichlorobenzyltributyl phosphonium chloride on growth and transpiration of slash pine. Nature (London), 200: 912. Cathey, H.M. and Stuart, N.W., 1961. Comparative plant growth-retarding activity of Amo 1618, Phosfon, and CCC. Bot. Gaz., 123: 51--57. Cohen, M.A., 1976. Herbicides and growth regulators for ornamentals and Christmas trees. Hortic. Crops Res. Set. 36, Dept. of Hortic, N.C. State Univ., p. 76. Pharis, R.P., Ruddat, M. and Phillips, C., 1967. Response of conifers to growth retardents. Bot. Gaz., 128(2): 105--109. Sachs, R.M. and Hackett, W.P., 1972. Chemical inhibition of plant height. HortScience, 7: 440--447. Sachs, R.M. and Maire, R.G., 1967. Chemical control of growth and flowering of woody ornamentals. J. Am. Soc. Hortic. Sci., 91: 728--734. Sachs, R.M., Hackett, W.P., Maire, R., Kretchun, T. and DeBie, J., 1970. Chemical control of plant growth in landscapes. Calif. Agric. Exp. Stn. Bull., p. 844. Sachs, R.M., Hield, H. and DeBie, J., 1975a. Dikegulac: A promising new foliar-applied growth regulator for woody species. HortScience, 10: 367--369. Sachs, R.M., DeBie, D., Kretchun, T. and Mock, T., 1975b. Comparative activity of commercially available maleic hydrazide formulations on several plant species. HortScience, 10: 366--367. Sanderson, K.C., 1973. Screening chemicals for controlling growth and flowering of Forsythia intermedia 'Zabel'. HortScience, 8: 477--479.