CULTIVAR, FERTILIZER, AND IRRIGATION AFFECT VEGETATIVE GROWTH AND SUSCEPTIBILITY OF CHRYSANTHEMUM TO WESTERN FLOWER THRIPS

'Fontana', 'Iridon', 'Pink Lady', 'Splendor', 'White Diamond', and 'Wh ite View Time' chrysanthemum (Dendranthema xgrandiflorum Ramat.) were grown for 10 weeks with N rates of 80, 160, or 240 mg.L-1 constant liq uid fertilization and irrigated at sufficient (high) or deficient (low ) amount. Cultivars differed in growth habit, and treatments significa ntly affected all variables measured. Plants fertilized with 80 mg.L-1 had lower leaf and stem dry mass, less leaf area, and were deficient in leaf N compared with plants fertilized with twice the amount of N, The highest stem dry mass was produced with 160 mg.L-1. Leaf and stem dry mass were reduced 25% for plants receiving low irrigation compared to those receiving high irrigation. In general, leaf area increased w hen fertilizer was raised from 80 to 160 mg.L-1 but differed by cultiv ar and irrigation regime when fertilizer was increased to 240 mg.L-1. Three weeks after the experiment started, electrical conductivity (EC) of runoff collected weekly from 'White Diamond' plants fertilized wit h 240 mg.L-1 exceeded the average EC of the irrigation solution. The 2 40 mg.L-1 treatment also resulted in excessive EC in the growing subst rate at the end of the experiment and reduced stem dry mass by 11% com pared with the 160 mg L-1 fertilizer regime. Substrate EC differed bet ween cultivars in response to fertilizer and irrigation. Significantly more adult western flower thrips [Frankliniella occidentalis (Pergran de)], 55% and 52%, were found on the foliage of 'Pink Lady' and 'Fonta na', respectively, than on 'Iridon', 'Pink Lady' and 'Fontana' had mor e immature thrips at the end of the experiment than 'Iridon' and 'Whit e View Time'. Fewer adults and immatures were found on plants fertiliz ed with 80 mg.L-1 than 240 mg.L-1. Fewer adults were detected in plant s under high versus low irrigation, while irrigation had no effect on the number of immatures. The simultaneous use of plant varietal resist ance and plant cultural growing techniques has the potential to lower thrips populations on chrysanthemum.