Phytophthora root rot, crown rot, leaf and stem blight, and fruit rot of cucumber can cause serious
losses, and are difficult to control. Although composts can be used successfully for control
of Phytophthora root rots, little is known about their effects on Phytophthora diseases of aboveground
plant parts. This research shows that the severity of Phytophthora root and crown rot of
cucumber caused by Phytophthora capsici was suppressed significantly in cucumber transplants
produced in a composted cow manure–amended mix compared with those in a dark sphagnum
peat mix. In split root bioassays, Trichoderma hamatum 382 (T382) inoculated into the compostamended
potting mix significantly reduced the severity of Phytophthora root and crown rot on
paired roots in the peat mix. This effect did not differ significantly from that provided by a
drench with benzothiadiazole (BTH) or mefenoxam (Subdue MAXX). Based on area under
disease progress curves, T382 also significantly reduced the severity of Phytophthora leaf blight
in transplants produced in the compost mix compared with controls not inoculated with T382.
Efficacy of T382 did not differ significantly from that provided by a drench with BTH. T382 remained
spatially separated from the pathogen in plants in both the split root and leaf blight bioassays,
suggesting that these effects were systemic in nature.