Hello! I am a MG in AACO. According to a Clemson paper on basil, I believe the basil in my community garden is stricken with downy mildew. Please confirm. The new basil seeds were planted this year in the basil bed that did poorly last year. The basil was going gangbusters until very recently. In Maryland this time of year, do you recommend the treatments proscribed in the Clemson paper? Is my basil done for the year? Are the spores in the soil? Can I replant from seed in this bed or in another? Can I transplant plants into another bed to improve air flow without transference of d.m. into that bed? In advance, thank you very much for your response.
Further research makes me more confident that the basil is affected with downy mildew, specifically the Peronospora belbaharii species. Additionally, I noticed the small spores on the underside of the leaf, which I thought was garden soil. Two additional resources were helpful, one From Wisconsin, and one from Cornell. I will have to change my growing practices to allow for much greater air flow, spacing and planting rows in the direction of prevailing winds, as well as trying new varieties. I do not believe my watering practices were at fault. The organism lives and is spread in water. I water the ground with a watering wand in mid-morning.
Anne Arundel County Maryland
Hi- yes, this is downy mildew of basil. Fortunately, there are a number of excellent resistant cultivars that are widely available to gardeners. We suggest that you pull up the diseased plants and plant seed of a resistant cultivar (you can plant through mid-August).
Some UME resources on this topic: