EFFECT OF WATER EXTRACTS OF SPENT MUSHROOM COMPOST ON APPLE SCAB IN THE FIELD

To control apple scab disease caused by Venturia inaequalis, aqueous e xtracts from two sources of spent mushroom substrate (SMS), anaerobica lly fermented for 7 days and amended with spreader-sticker, were appli ed at weekly intervals to apple trees (cv. McIntosh) from green-tip to petal-fall and biweekly thereafter. Trials were conducted for three s easons at two locations in Wisconsin. Both extracts significantly redu ced (alpha = 0.05) the leaf area affected by scab relative to water an d spreader-sticker controls as evaluated by the Horsfall-Barratt scale . Disease incidence was similarly decreased but to a lesser extent. Ex tracts were not as effective in inhibiting disease as captan sprayed a t the same intervals. No difference was detected between extracts with and without spreader-sticker. Higher populations of bacteria, which p ersisted for at least 1 month after the final spray, were detected on leaves treated with the extracts. No differences were found in total n umbers of fungi. Inhibitory activity of extracts, assessed as in vitro inhibition of Venturia conidia germination, was monitored over time f or extracts prepared from SMS stored under different conditions. For o ne source of SMS, neither time nor storage conditions (outdoors uncove red or indoors in sheds) affected inhibitory activity of extracts. Dec line in efficacy of the other source was apparent by 13 weeks relative to unstored compost, although not between storage regimens.