I've never had it on basil, just squash leaves, but I would be sure to sterilize all equipment that had contact with it in a bleach solution. I think it is also spread by spores and the wind so it is probable that the soil is infected too unless your area winter kills.

Good ventilation around and under leaves helps keep the plants dry so they are less susceptible.

Dont people use neem or a milk spray solution to treat it once it appears on leaves? Basil probably couldn't be saved though.

Cindy, there are no basil varieties that are resistant to BDM, Peronospora belbahrii. I'd be reluctant to grow any more in a garden where it had been present for two years.

Chemical control is not particularly effective because it's not a true fungal organism and doesn't respond well to even the super powerful fungicides used by professional growers.

Unfortunately, the growers are having a very difficult time keeping the disease out of the greenhouses. It's even carried in seeds.

You could try growing some in a very sunny location in a container, but the spores are wind borne and easily carried for miles. If you are purchasing infected plants in the first place, then there's zero chance.

Avoid overhead watering, trim stems in order to increase light penetration and wind circulation and keep your fingers crossed

Most importantly, learn the early signs of infection (yellowing) and remove the plant immediately.

P.S. It cannot be controlled with milk....it's not powdery mildew.

rhizo-

Thank you for this information. It's very helpful

I ordered a variety of seeds that Johnny's sell that they claim to be less susceptible to downy mildew.

http://www.johnnyseeds.com/p-9316-eleonora.aspx

Additionally, I ordered some Greek Columnar basil plants.

Do you know anything about treating the plants with hydrogen peroxide?

I seem to be finding conflicting information about using this treatment for downy mildew and would like to know if anyone has tried using H2O2?

http://awaytogarden.com/basil-pressure-fight-devastating-downy-mildew/

Cindy