Cultivar, fertilizer, and irrigation affect vegetative growth and susceptibility of chrysanthemum to western flower thrips

'Fontana', 'Iridon', 'Pink Lady', 'Splendor', 'White Diamond', and 'White View Time' chrysanthemum (Dendranthema xgrandiflorum Ramat.) were grown for 10 weeks with N rates of 80, 160, or 240 mg.L-1 constant liquid fertilization and irrigated at sufficient (high) or deficient (low) amount. Cultivars differed in growth habit, and treatments significantly 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 when fertilizer was raised from 80 to 160 mg.L-1 but differed by cultivar 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 with 240 mg.L-1 exceeded the average EC of the irrigation solution. The 240 mg.L-1 treatment also resulted in excessive EC in the growing substrate at the end of the experiment and reduced stem dry mass by 11% compared with the 160 mg.L-1 fertilizer regime. Substrate EC differed between cultivars in response to fertilizer and irrigation. Significantly more adult western flower thrips [Frankliniella occidentalis (Pergrande)], 55% and 52%, were found on the foliage of 'Pink Lady' and 'Fontana', respectively, than on 'Iridon'. 'Pink Lady' and 'Fontana' had more immature thrips at the end of the experiment than 'Iridon' and 'White View Time'. Fewer adults and immatures were found on plants fertilized with 80 mg.L-1 than 240 mg.L-1. Fewer adults were detected in plants under high versus low irrigation, while irrigation had no effect on the number of immatures. The simultaneous use of plant varietal resistance and plant cultural growing techniques has the potential to lower thrips populations on chrysanthemum.