Basil Downy Mildew Research Results – Long Island

Meg McGrath, Long Island Horticultural Research & Extension Center, mtm3@cornell.edu:

Major findings from two experiments conducted on field-grown sweet basil at LIHREC in 2022 are:

Resistant Varieties.  All provided very good to exceptional control of downy mildew.  As usual, downy mildew quickly became very severe on the susceptible variety (DiGenova).  The Prospera commercial varieties and the experimentals with the new Pb2 resistance gene developed very few potential downy mildew symptoms that lacked pathogen spores. The 4 DMR Rutgers varieties provided 95-99% control, which was better than in 2020 and 2021, perhaps due to conditions being drier and thus less favorable for downy mildew in 2022. 

Conventional Fungicides.  The preventive program consisting of an alternation of Ranman + K-Phite, Presidio + K-Phite, and Orondis Ultra provided good suppression of downy mildew on a susceptible variety (DiGenova; 66%), but more effective control (96%) was achieved with the untreated resistant variety, Rutgers Passion DMR.  Due to the high degree of suppression achieved with this resistant variety, neither the preventive or IPM (started after seeing symptoms) fungicide programs significantly improved control. 

In these experiments incidence of affected leaves (percent leaves with sporulation of the pathogen visible on the underside) was assessed rather than severity because any amount of symptoms renders a leaf unmarketable. 

An integrated program with fungicides applied to a resistant variety is recommended to ensure effective control when conditions are highly favorable or a new pathogen genotype is present able to overcome host resistance.

See basil downy mildew research webpage for more information, results tables, and photographs from these experiments and others conducted in the past.