A semifield assay was conducted from 2009 to 2011 to distinguish between different preventive methods
of reducingVerticilliumspp. in spinach seed production. The seed treatments for controlling seed
infection levels included Thiram, Signum,Trichoderma harzianum, Gliocladium roseumand Natural II, and
these were tested in naturally infested and uninfested soil. Even though seed treatment by Thiram and
Signum in all cases reduced the incidence ofVerticilliumspp. on the harvested seed, the soil type had a
large influence on the subsequent disease pressure as a significant effect of soil was seen in 2010 and
2011 and a non-significant effect of seed treatment onVerticilliumspp. was observed in all experimental
years. As no interaction between soil and seed treatment was observed, the seed treatment had no effect
on the disease pressure on the seeds subsequently harvested from the infested soil.