Inhibition of fungal pathogens of woody plants by the plant growth regulator paclobutrazol

Mycelial growth in vitro of eight plant pathogenic fungi was inhibited 25-100% by the gibberellin inhibitor paclobutrazol. This chemical is currently registered for use on landscape trees and shrubs to minimize shoot growth and extend pruning intervals. Fungicidal activity was evident at dosages 200 times more dilute than the typical rate recommended for field use to retard shoot growth, and the effect persisted indefinitely. Spore germination was reduced by a factor of at least two, and as much as 66 x compared to the control in four of six fungi tested. Rhizomorph production in Armillaria gallica Marxmuller & Romagnesi was almost completely eliminated. (C) 2000 Society of Chemical industry.