Downy Mildew. If you have ever had to deal with it in your greenhouse (or worse, your garden) you will be clenching your teeth in dread right now. If you are not familiar with it, count your blessings. It would be wise to do a bit of reading, though, just so you know what you are dealing with should you ever have it happen to you.
Thanks to the Marin Rose Society for publishing this resource.