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

Mycelial growth in vitro of eight plant pathogenic fungi was inhibited 25-1 00% by the gibberellin inhibitor paclobutrazol. This chemical is currently registered for use on landscape trees and shrubs to minimize shoot growth a nd extend pruning intervals. Fungicidal activity was evident at dosages 200 times more dilute than the typical rate recommended for field use to retar d shoot growth, and the effect persisted indefinitely. Spore germination wa s 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 ga llica Marxmuller & Romagnesi was almost completely eliminated. (C) 2000 Soc iety of Chemical industry.