Filtration to Eliminate <i>Phytophthora</i> spp. from Recirculating Water Systems in Commercial Nurseries

Fig. 6. Percent recovery of Phytophthora spp. from water samples taken before and after filtration with SSF or with LGF.  SSF = slow sand filtration, LGF = lava grain filtration.
  a Percent recovery based on the number of positive tissue pieces out of
      15 tested for each water sample.
  b Filter was switched off for cleaning at sampling date.
  c No sampling because filter was under modification.



Image from Plant Health Progress article:
Filtration to Eliminate Phytophthora spp. from Recirculating Water Systems in Commercial Nurseries