Factors in testing fungicides against powdery mildews. I. A slide spore‐germination method of evaluating protectant fungicides

SUMMARY The germination of conidia of Erysiphe betae, E. graminis, E. horridula, E. martii, Oidium begoniae, an Oidium sp. from Crepis taraxacifolia and Uncinula necator was studied on dry uncoated glass slides and on dry slides with the following coatings: cellulose acetate (C.A.); the polyvinyl acetate derivative Gelva 7; nitrocellulose (collodion); and ethyl cellulose. Slides dusted with conidia were incubated at 21±1° C. in a saturated atmosphere in the dark. Germination over 85% and as high as 96±4% was obtained on slides coated with C.A. or Gelva 7. The germination on slides coated with collodion was lower and abnormal, the germ‐tubes growing away from the substrate. The possibility of studying the toxicity of chemicals towards conidia of powdery mildew fungi by incorporating them into a C.A. layer used as a coating for glass slides was examined. ‘Dinocap’, a captan analogue and members of a homologous series of n‐alkyl fatty acids were used, with conidia of E. betae, E. horridula, E. martii and O. begoniae as test organisms. The results obtained demonstrated the potentialities of the method.