Paclobutrazol Drench Activity Not Affected in Sphagnum Peat-based Substrates Amended with Pine Wood Chip Aggregates

Processed pine (Pinus sp.) wood has been investigated as a component in horticultural substrates (greenhouse and nursery) for many years. Specifically, pine wood chips (PWC) have been uniquely engineered/processed into a nonfiberous blockular particle size, suitable for use as a substrate aggregate. The purpose of this research was to determine if paclobutrazol drench efficacy is affected by PWC used as a substitute for perlite in a peat-based substrate. Paclobutrazol drench applications of 0, 1, 2, and 4 mg/potwere applied to 'PacinoGold' sunflower (Helianthus annuus); 0.0, 0.25, 0.50, and 1.0 mg/pot to 'Anemone Safari Yellow'marigold (Tagetes patula); and 0.0, 0.125, 0.25, and 0.50 mg/pot to 'Variegata' plectranthus (Plectranthus ciliates) grown in sphagnum peat-based substrates containing 10%, 20%, or 30% (by volume) perlite or PWC. Efficacy of paclobutrazol drenches for controlling growth of all three species was unaffected by substrate composition. We concluded that substituting PWC for perlite as an aggregate in peat-based substrates should not reduce paclobutrazol drench efficacy, variability in PWC products indicates that efficacy should be tested before large-scale use. The variability results from wood components not being engineered and processed the same across manufacturers, meaning that they are often incapable of improving/influencing the physical and chemical behavior of a substrate similarly.