Lettuce Best Practice - Department of Primary Industries

Farm Services Victoria 32Downy MildewBremia latucaeEffective IPM Rating √ √ √ √ √ResistantvarietiesavailableThere aremany types(or races) ofthis fungus.Some lettucevarietiesclaimresistance tosome racesCritical Comments: Use resistant varieties and monitor crops closely and apply protectivemeasures when conditions suitable for infection.Rotation Crop Cultural Practices Chemical Control Conflicts /IssuesHigh Risk Disease Nutrition Irrigation Hygiene Other Chemical IPM IssuesBreakCool, dampconditions.Free moistureon plantleaves.High riskfollowinglettuce crops,near globeartichoke,endive,chicory andornamentalhost plants.Seed shouldbe fungicidetreated.Avoidplantingnear otherlettuce fieldsas airbornespores canbe dispersedfrom one cropto the otherby the wind.Crop rotationis important.ExcessiveNitrogenmay makelettuce moresusceptible.Avoid highnitrogenlevels.Avoidwateringseedlingsfrom 8.00am-12.00pm asmost sporesare releasedduring thisperiod,irrigation willact to washspores out ofthe air andprovide wetleaf surfacesfor them toinfect plants.Use widerplant spacingto facilitatebetter airmovementand leafdrying.Transplantsshould beprotectedwithfungicides toavoid Downymildew beingintroducedinto the field.Predictivemodels fordowny mildewon lettuceare underevaluationworld-wide.Align plantspacing thatallows formaximumventilation.Subsequentplantingsshould beup- wind ofcurrent crops.Applypreventativefungicidesbefore thediseasedevelopsbased onweatherconditions.Rotate withcurativefungicideswhenconditionsare ideal forinfection.Chooseresistantvarietieswherepossible.More difficultto controlas the plantages andcrop densityincreases.Control mayconflict withoptimumirrigationtiming duringthe nightfor tipburnmanagement.