Epifluorescence microscopy and low temperature scanning electron
microscopy were used to document the development of Uncinula
necator on vine leaves and the antifungal effects of kresoxim-methyl
and penconazole. Post-germinational growth and development
followed a regular time course which was classified into 10 stages.
Kresoxim-methyl was applied at a range of concentrations and at different
times before and after inoculation. In glasshouse trials
at moderate relative humidity (60%), all pre-infectional applications
completely inhibited conidial germination. Lower efficacies were
observed with detached leaves at high humidity in Petri dishes. Post-infectional
applications of at least 8 mg a.i. l−1 inhibited
sporulation and mycelial growth and 67 mg a.i. l−1
caused a partial collapse of surface structures.
Penconazole applied at 17 mg a.i. l−1
did not inhibit germination, but prevented hyphal development and caused
with hyphal tip swelling. Pre- and post-infectional treatments had similar
effects. Applications made 3 d after inoculation increased
multiple appressoria and conidiophore formation.