New basil downy mildew images added to the basil downy mildew photo gallery:
Under humid conditions the pathogen produces an abundance of dark spores as shown in photographs below from Fran Smith in Pennsylvania who submitted them for confirmation of her report to the monitoring program.
Hi Margaret,
One source of this disease comes from gardening soil sold by major manufacturers through retail outlets.
In my case, I bought 12-40 lb. bags of Miracle Grow garden soil. Shortly after transplanting the starts into the soil, every species contracted the disease, especially Basil.
I discovered the connection when I re-opened a half used bag and discovered the powdery mildew flourishing in the soil.
My guess is contamination at the factory is simply spread throughout the U.S. as the product is distributed nation-wide.
Ernest
Biologically it is not possible for the basil downy mildew pathogen to grow on soil or survive in soil. All downy mildew pathogens are ‘obligates’ – they only develop on living plant tissue – they cannot grow on anything other than plant tissue. What you saw developing on the soil mix is a saprophytic (non-pathogenic) organism. A few downy mildew pathogens can produce a type of spore able to survive in soil, but not the basil downy mildew pathogen, and these spores would only be in the ground where affected plants were present previously, not bagged growing media (which typically is soil-less). The fact you saw plants other than basil affected is further indication you do not have basil downy mildew – this pathogen can only infect basil.
You sold me. However, my basil, tomatoes, squash, tarragon, peppers, etc. have powdery mildew…exactly like your photos. So, can basil contract other forms of mildew?
Thanks