Management of Lettuce Downy Mildew with Fungicides

Richard N Raid, Dezhi D Sui


Incited by the obligate parasite Bremia lactucae, downy mildew is one of the most devastating diseases of lettuce (Lactuca sativa L.) worldwide. Attempts to manage this fungal disease using host-plant resistance have frequently failed due to the development of new races of the pathogen. Therefore, chemical control is of the utmost importance in humid areas where environmental conditions are very favorable for disease development. Numerous fungicide field trials have been conducted in south Florida on both muck and sandy soils over the past several years with definitive results. Of currently registered compounds, mandipropamid (Revus) and fenamidone (Reason) have repeatedly provided the highest levels of control, with no significant difference between the two. Presidio (fluopicolide), dimethomorph (Forum), dimethomorph plus ametoctradin (Zampro), cyazofamid (Ranman), and propamocarb (Previcur Flex) have also provided significant control. With regard to new chemistries, the experimental compound V-10208 has looked very promising when applied foliarly. As a group, the aforementioned fungicides represent a wide array of different modes of action, meaning that they may be alternated or tank-mixed with other fungicides in a program to prevent fungicide resistance. This is
indeed fortunate, as lettuce downy mildew has developed insensitivity in the past. With potassium phosphites and the broad spectrum EBDC fungicide mancozeb holding lettuce registrations, lettuce growers now have a wide selection of fungicides for managing this important disease. However, prevention and cultural practices, such as destroying old crop debris, should also be part of the program.


Bremia lactucae, Lactuca sativa, chemical control, disease management

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Proc. Fla. State Hort. Soc.     ISSN 0886-7283