The Influence of Cultural Factors on the Direct Antifungal Activities of Fosetyl‐Al, Propamocarb, Metalaxyl, SN 75196 and Dowco 444

The effects of the systemically active disease control compounds Fosetyl‐Al, Metalaxyl, Propamocarb, SN 75196 and Dowco 444 on the growth, in vitro of two Oomycetes have been studied. Fosetyl‐Al, Propamocarb and SN 75196 are only weakly antifungal, and their activities, in vitro are sensitive to nutrition, pH and temperature. Factors which increase the growth of the fungus decrease its sensitivity to these compounds. These compounds display no selectivity for Oomycetes in vitro which belies their reported selectivity in vivo. Metalaxyl and Dowco 444 are selective for, and very active against Oomycetes in vitro and this activity could account for their modes of action in vivo.