Initial symptoms include large, angular or blocky, yellow areas visible on the upper surface.

As a result of numerous infectious sites, leaves might show a blighted appearance if the disease continues to spread.

In disease-favorable conditions (cool nights with long dew periods), downy mildew will spread rapidly, destroying leaf tissue without affecting stems or petioles.

[5] One floricolous species, Peronospora violacea, causes its host Succisa pratensis to produce longer, pinker petals,[7] and abort its anthers.

[8] Because the downy mildew pathogen does not overwinter in midwestern fields, crop rotations and tillage practices do not affect disease development.

Therefore, planting early season varieties may further reduce the already minor threat posed by downy mildew.

[4] When downy mildew does pose a threat, the removal and destruction of plants displaying symptoms is good practice.

[9] In Canada, a mixture of zoxamide and mancozeb was registered for control of the mildew under the trademark Gavel (fungicide) as early as 2008.

Choosing resistant cultivars, in combination with other prevention and control measures, can help growers with high downy mildew pressure still produce a viable crop.

[11] Downy mildew of basil caused by Peronospora belbahrii has been a huge problem for both commercial producers and home growers.

Tufts of grayish to pale-colored sporangiophores on the underside of leaves easily distinguish the infection from other foliar diseases.