Following pictures were taken 16 December 2021. Leaves were from a home garden on Long Island where powdery mildew had been developing on kale, which likely was the source of the pathogen (Erysiphe cruciferarum). Symptoms were the typical white patches of fungal growth on upper leaf surfaces. Very few symptoms developed on arugula in contrast with the kale. Few spores were seen when the leaves were examined under a dissection microscope. Powdery mildew had not been seen in previous years at this location where arugula is grown from spring until temperatures in winter are cold enough to kill arugula. This observation documents the potential for this disease to occur in the region but also suggests it likely will not be important, at least in field-grown crops. Powdery mildew fungi produce spores dispersed in air currents that are capable of moving long distances.
However, powdery mildew was listed as a big challenge by 1 of 51 responders to a survey about arugula diseases and other production issues in Aug 2021. This grower produces arugula in high tunnel in the northeast.
Powdery mildew has been reported as a minor disease of arugula in California, Arizona, and Florida. It was recently reported (September 2012) for the first time in Australia with extensive leaf and stem symptoms at the late flowering stage (Plant Disease 97:1256).
Please report sightings of powdery mildew in arugula to Meg McGrath to contribute to knowledge about it.
