From Meg McGrath, Long Island Horticultural Research & Extension Center, mtm3@cornell.edu:
A gardener in Westhampton Beach posted a report with confirming pictures at the Basil Downy Mildew Monitoring website. Symptoms (yellowing of leaves) was first noticed 7/15. Downy mildew pathogens are host specific, thus this is not the same pathogen affecting cucurbits. Similar to the Cucurbit Downy Mildew website, at the Basil Downy Mildew website you can sign up for alerts and there is a map of reported occurrences.
Please report when you see this disease.
For more information about this disease and its management see the Cornell Vegetables website.
Be on the lookout for more severe development of downy mildew on resistant varieties than seen in the past. PLEASE report to me if you see. Last year there were a few reports of severe downy mildew on Prospera in the U.S. The pathogen obtained from affected plants was shown to be genetically different from that on other plants. A new pathogen race has been confirmed elsewhere in the world. Prospera exhibited excellent suppression in the variety evaluation at LIHREC in 2021 as in previous years. The Rutgers DMR varieties have not been performing as well as they did but were still much less severely affected than varieties with no resistance.
Research is underway at LIHREC this summer to evaluate resistant varieties, including those with a new gene for resistance, and both organic and conventional fungicide programs applied to susceptible or resistant variety on a preventive or IPM (after symptoms seen) schedule.