From Clemson Plant Pathologist Tony Keinath.
One of the rainstorms the week of June 5, 2023, brought basil downy mildew spores with it to Coastal REC. On Friday, June 9, all four cultivars in our demonstration were healthy and more than ready to harvest.
On Monday, June 12, this is what we found.
Basil downy mildew spores probably spread much the same way as cucurbit downy mildew spores do. The rainstorm not only brought spores but also deposited the spores on the basil leaves and wetted the leaf surfaces, which allowed the spores to germinate and infect hundreds of basil leaves. Each leaf was infected by a different spore, so you can see that many spores arrived at once.
In this demo, we didn’t need to rate downy mildew to see the clear results.
With two good resistant cultivars, there is no reason to grow older basil cultivars that are susceptible to downy mildew. Both resistant cultivars are available as conventional and organic seed from numerous seed companies.
The South Carolina Grower 