Downy mildew in vineyards - Department of Agriculture and Food

PAGE 16DOWNY MILDEW IN VINEYARDS(Note: In table grapes pre-infectionfungicides should only be used providedit is prior to 10 mm berry size as sprayresidues on berries may occur).Post-infection fungicides (applied assoon as possible after an infectionevent)Post-infection (eradicant) fungicidesare systemic and penetrate the vinetissue killing the downy mildew fungusfrom within the vine tissue. Use of thesefungicides involves withholding spraysuntil an infection event has occurred.Relying on post-infection fungicidesrequires careful monitoring and has agreater risk of downy mildew becomingestablished. However, if downy mildew isnot established in the region or vineyardand few possible infection events occur ithas the advantage of using fewer spraysthat have greater effectiveness.Post-infection fungicides work bestwhen applied as soon as possible afteran infection event - within fi ve days ofinfection and before oilspots appear. Noadditional spraying should be requireduntil weather conditions favour anotherpossible infection event. In this situation,pre-infection fungicides may be usedonce again.Once the fungus is visible it is diffi cultto kill. A single post-infection spray isusually not effective, although it mayreduce the number of spores and limitspread of the disease. Hence, follow upLarge oilspots killed by well-timed sprays ofpost-infection fungicides.