Disclosed herein are compositions and methods that involve recombinant polynucleotide molecules, such as single or double-stranded DNA or RNA molecules, also referred to “triggers”, that are useful for controlling or preventing E. necator infection, or recombinant DNA constructs for making such RNA molecules or for making transgenic grape plants resistant to E. necator infection. In some embodiments, polynucleotide triggers are provided as topically applied agents for controlling or preventing infection of a plant by E. necator.