Commercial Disease Controls
The Pennsylvania State University
Cooperative Extension

Leeks

Disease Control

Purple Blotch and Downy Mildew
Begin in fall as soon as transplants are set out. Alternate the following at 10-day intervals as long as night temperatures are warm.

Forum--6 oz 4.18SC/A (for downy mildew only; must be tank mixed with another fungicide effective for downy mildew), or chlorothalonil (Bravo, Echo, Equus--l.5-3 pt 6F/A or OLF; Do not apply more than three times per season) with any of the following fungicides:
azoxystrobin (Quadris--6.2 - 12.3 oz 2.08F/A for Purple blotch or Quadris--9.2 - 15.4 oz 2.08F/A for downy mildew or Amistar--2-4 oz 80WDG/A for Purple blotch or Amistar--3-5 oz 80WDG/A for downy mildew), or
Cabrio--8-12 oz 20EG/A, (use 12oz/A for downy mildew), or
Endura--6.8 oz 70W/A (for purple blotch only), or
Pristine--10.5-18.5 oz 38WP/A (for purple blotch) or 18.5 oz 38WP/A for downy mildew suppression.

White Rot
This disease is severe only on overwintered leeks. Practice crop rotation and use preplant soil fumigation with one of the materials listed in the "Soil Fumigation" section.

Note: Where trade names are used, no discrimination is intended and no endorsement by the Cooperative Extension Service is implied. Information provided is intended for consideration by the user, but is not intended to be a recommendation. Production decisions should be based on consideration of many types of information (scientific, experiential, economic, legal, etc.) available to the user.