Method of Application Affects Response of Hollyhock to Paclobutrazol

Table 1. Effect of paclobutrazol (paclo) on plant height and number of leaves developed on hollyhock at 2, 4, or 6 weeks after treatment. All application techniques were designed to deliver 0.10 mg paclo/10-cm Our objective was to determine the efficacy of a given dosage of β-[(4-chlorophenyl)methyl]-α-(1,1-dimethylethyl)-1H1,2,4-triazole-1-ethanol [paclobutrazol (paclo)] applied using differing volumes and application methods [i.e., compressed air, airassisted electrostatic spraying (Law et al., 1992), fog spray, drench, and a spike] on hollyhock (Alcea rosea L.). ‘Powderpuff Mix’ hollyhock plants, established in 580-cm pots from plugs, were purchased on 14 Sept. 1993. Paclo (Bonzi, Uniroyal Chem. Co., Middlebury, Conn.) was applied to actively growing plant material on 24 Sept. 1993. At the time of treatment, plants were in a rosette form with five leaves and a maximum height of ≈15 cm (measured from pot rim). Greenhouse air averaged 26C day/ 17C night with a mean photosynthetic photon flux of 14.1 mol•m•day. Plants were watered overhead as necessary to prevent visible stress and were fertilized weekly with 200 mg N/liter using 20N–4.4P–16.6K (Peter’s General Purpose 20–10–20; Grace-Sierra, Cambridge, Mass.). Treatments were designed to apply an active ingredient dose equivalent to a 50-mg•liter paclo spray at the label-recommended volume of 210 ml•m. Medium surfaces were not covered. Treatments resulted in 10 mg paclo/ m or ≈0.10 mg/pot, except the spike, which provided ≈0.125 mg/pot. Application methods included spray applications with a handheld compressed-air sprayer (210 ml•m; Gilmour 201P at 30 psi, Gilmour, Somerset, Pa.), a hand-held electrostatic sprayer (23 ml•m; model EPS-5; Electrostatic Spraying Systems, Watkinsville, Ga.), or a fixed-position fog sprayer (10 ml•m; LVM-400 sprayer; Ball Seed Co., East Chicago, Ill.); a drench of 50 ml/pot of a 2-mg paclo/liter solution; and a paclo spike (Barrett et al., 1994). Each spike