HortTechnology ● Oct./ Dec. 1996 6(4) 396 RESEARCH UPDATE under long-day conditions (Table 2). Temperature also affected plant qual- ity. Plant quality was highest, across irradiance and photoperiod treatments, when plants were grown at 16 °C compared to other temperatures (Fig. 2). Discussion Scion necrosis probably is related to photoperiod and temperature ef- fects on cacti reproductive develop- ment, apical dominance, or both. Factors controlling flowering in many cacti are unclear. Many cacti have an obligate or facultative vernalization re- quirement (Cullman et al., 1984; per- sonal observation). Furthermore, flowering is increased when cacti are vernalized and then placed under short- day vs. long-day conditions (Cullman et al., 1984). Some cacti, notably Schlumbergera truncata (Thanksgiv- ing cactus) and R hipsalidopsis rosea (Easter cactus), will flower under short days without receiving any cold treat- ment (i.e., they may not have any vernalization requirement). If C. silvestrii or H. trigonus are short-day plants, data presented here suggest that flat-grafted cacti must be grown under apparent vegetative conditions (long days and warm temperatures) to inhibit scion necrosis. The association between root- stock axillary shoot development and scion necrosis suggested that necrosis might be related to loss of apical domi- nance and subsequent axillary shoot development on the rootstock. Re- duction in apical dominance of many plants often is associated with reduced daylength (Phillips, 1969). Chamaecereus silvestrii (yellow sport) scion necrosis may be an artifact of rootstock behav- ior if necrosis has occurred when the rootstock failed to translocate needed assimilates to the scion. Carbohydrate translocation often is correlated posi- tively with irradiance (Christy and Swanson, 1976; Hartt, 1965; Troughton and Currie, 1977). Differences in my study probably are associated with pho- toperiod effects on apical dominance and/ or reproductive state only since there was no effect of irradiance on scion necrosis. H owever, it cannot be assumed that scion necrosis is associ- ated exclusively with rootstock effects because axillary shoot development and scion necrosis occur nearly at the same time; removal of a sink (death of the scion in this case) promotes axillary shoot development (Tamas, 1987). Graft necrosis is reduced greatly and plant quality was greatest when plants received night interruption light- ing with incandescent lamps from 2200 to 0200 HR and when plants are grown at a constant 20 °C. In addition, al- though not statistically significant, supplemental lighting increased over- all plant quality by intensifying of scion color and apparent size. Literature Cited Carter, F.M. 1973. Grafting cacti. Horti- culture 51(3):34–35. Christy, A.L. and C.A. Swanson. 1976. Control of translocation by photosynthe- sis and carbohydrate concentrations of the source leaf, p. 329–338. In: I.F. Wardlaw and J.B. Passioura (eds.). Transport and transfer processes in plants. Academic, New York. Cullman, W., E. Gotz, and G. Groner. 1984. Encyclopedia of cacti. Timber Press, Portland, Ore. Hartt, C. 1965. Light and translocation of 14C in detached blades of sugar cane. Plant Physiol. 40:718–724. Lamb, E. and B. Lamb . 1976. The pocket encyclopedia of cacti and succulents. Macmillan Pub. Co., New York. Mabe, R . 1974. Gardening with cactus. Potpourri Press, Greensboro, N.C. Meadow, K . 1976. Cacti and other succu- lents for your home. Brombacher Books, Richmond, Calif. Phillips, I.D.J. 1969. Apical dominance, p. 165–202. In: M.B. Wilkins (ed.). The physi- ology of plant growth and development . McGraw-Hill, London. Tamas, I.A. 1987. Hormonal regulation of apical dominance, p. 393–410. In: P.J. Davies (ed.). Plant hormones and their role in plant growth and development. Martinus Nijhoff, Dordrecht, The Netherlands. Troughton, J.H. and J.B. Currie. 1977. Relations between light level, sucrose con- centration, and translocation of carbon 11 in Zea maysleaves. Plant Physiol., 59:808–820. Response of Four Vegetable Crops to Fluridone- treated Irrigation Water Stratford H. Kay 1 , Ross B. Leidy 2 , and David W. Monks 3 ADDITIONAL DDITIONAL DDITIONAL DDITIONAL DDITIONAL INDEX INDEX INDEX INDEX INDEX WORDS WORDS WORDS WORDS WORDS. . . . . nontarget effects, aquatic herbicide, Sonar, 1- methyl-3-phenyl-5-[3- (trifluoromethyl)phenyl]-4(1 H )- pyridinone, soil type, tomato, Lycoper- sicon esculentum, sweet corn, Zea mays , bell pepper, Capsicum annum, cucumber, Cucumis sativus SUMMARY UMMARY UMMARY UMMARY UMMARY. . . . . Greenhouse studies examined the effects of an aquatic herbicide (fluridone) in irrigation water on four vegetable crops grow- ing on two soils. Tests on Fuquay loamy sand (0.3%humic matter) and Portsmouth fine sandy loam (4.1% humic matter) examined fluridone concentrations ≤250 μg·L –1 . Injury to sweet corn ( Zea may L.), cucumber ( Cucumis sativus L.), bell pepper ( Capsicum annum L.), and tomato ( Lycopersicon esculentum L.) on these soils varied with soil type and stage of plant growth. Seedlings or new transplants were more susceptible to fluridone damage than older plants. All plants showed more injury on Fuquay loamy sand, which had the lowest humic matter content. Injury to cucumber occurred only to seed- N orth Carolina State University, R aleigh, N C 27695. 1 A ssociate professor, Department of Crop Science. 2 Professor, Department of Toxicology. 3 A ssociate professor, Departm ent of H orticultural Science. This project was funded by the N ational Pesticide Impact A ssessment Program, Southern R egion, under Contract SR 92-53-0-N C. Fluridone for these studies was provided by DowElanco. We are grateful to S.T. H oyle, R .I. H unt, R .J. Mills, and J.L. Boyd for providing technical assis- tance, to M.A. Gumpertz for statistical consultation, and to A.D. Worsham and W.A. Skroch for providing comments on the manuscript. A dditional assistance was provided by C.R. Coley, A.G. Poovey, and A. Bryan. Mention of a trade name does not constitute an endorse- ment of a product to the exclusion of others which may be equally suitable for similar use. The cost of publishing this paper was defrayed in part by the payment of page charges. Under postal regulations, this paper therefore must be hereby marked advertisement solely to indicate this fact.