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  • Author or Editor: David Williams x
  • Journal of the American Society for Horticultural Science x
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Operation management techniques, such as linear programming (LP), can provide producers and managers with greater quantities of information and, from this, more informed, up-to-date decisions can be made. Linear programming techniques were applied to data from ten container plant nurseries to determine possible production systems, their inputs, and to maximize profit. Models were developed for large (average, 27 ha) and small (average, 5 ha) container nurseries. Plant type and container size were used interactively as decision variables (activities) in the models. The small nursery model had 44 plant type alternatives and the large nursery model had 87. Resources included in the constraints were equipment, materials, and labor used to produce each plant type. The actual constraint values determined from survey information are provided, as well as a multiperiod model and a theoretical model.

Open Access

In three experiments, damage caused by twospotted spider mite (TSSM; Tetranychus urticae Koch) was correlated with the quality of ivy geranium [Pelargonium peltatum (L.) L'Her ex Aiton], and the action threshold for TSSM on ivy geranium was developed. Ivy geranium quality was measured as overall plant quality—plant size and form, and leaf greenness and glossiness—leaf browning, and leaf distortion. Young plants with high initial TSSM numbers (30 TSSM/plant) exhibited the greatest damage, suggesting that monitoring for TSSM early in the plant production cycle is necessary to prevent extensive damage. The leaf distortion index and overall plant quality were correlated with cumulative TSSM density and marketability in 4-week-old plants infested with 30 TSSM, whereas leaf browning was not correlated with either. Thus, either leaf distortion or overall plant quality can be used to measure economic damage resulting from TSSM. The action threshold for TSSM on ivy geranium was determined using overall plant quality. When the predatory mite, Phytoseiulus persimilis Athias-Henriot, is used to control TSSM, the action threshold was found to be 2 TSSM/leaf. Results also showed that fertilizer combinations of 8 or 24 mm nitrogen and 0.32, 0.64, or 1.28 mm phosphorus had no effect on cumulative TSSM density. When P. persimilis was released at predator: prey ratios of 1:60, 1:20, and 1:4, TSSM damage, measured as both leaf distortion and overall plant quality, was significantly reduced at 1:4 and 1:20, but not at 1:60. A 1:4 rate resulted in the most marketable plants. These results suggest that P. persimilis should be released at a rate of 1:4 when the TSSM action threshold is reached.

Free access

This study was undertaken to determine if endogenous IAA content and axillary bud development correlate with phenylalanine ammonia-lyase (PAL) induction and russet spotting (RS) susceptibility among RS susceptible and resistant cultivars of Iceberg lettuce (Lactuca sativa L.). Final levels of ethylene-induced PAL activity and RS development were highly correlated among cultivars, field conditions, and harvest dates. Harvested Iceberg lettuce midribs contained relatively low amounts of free IAA (maximum of 5.2 ng·g-1 fresh weight). There was poor correlation between free IAA content in lettuce leaf midribs and final RS development among all cultivars, growing conditions, and harvest dates. Axillary bud development, as measured by the number of visible buds per head, bud weight, or bud length, were not significantly correlated with final RS development or midrib IAA content. Cultivars with higher initial free IAA content lost much of their IAA after 8 days storage at 5C in air ± ethylene.

Free access