Management Strategies for Lettuce Drop in Arizona and California Lettuce Drop Barry Pryor Department of Plant Pathology University of Arizona The Pathogens: Sclerotinia minor and S. S. sclerotiorum sclerotiorum • • • • over 1500 recorded hosts cottony rot, white mold, watery rot on fruits, flowers, leaves, stems, and roots growth is favored by moist conditions both species produce longlong-lived resting structures known as sclerotia S. minor Eruptive Germination Lettuce drop disease cycle S. sclerotiorum S. minor 1 Lettuce drop disease cycle Apothecium discharging ascospores Integrated disease management of lettuce drop host resistance cultural practices chemical control biocontrol 2 Host Resistance No commercially acceptable cultivar exist Most breeding programs have focused on Cultural Practices S. minor -“slow“slow-dying” phenotypes have been described Little progress has been made on resistance to S. sclerotiorum Crop rotation -broccoli rotation for control of S. minor -fallow rotation for control of S. sclerotiorum Irrigation water management is key to reduced disease -furrow…sprinkler…subsurface drip 2003 Yuma Fungicide Trials Chemical control of lettuce drop Treatment Rovral 4F Ronilan 50DF Endura 70WG Serenade AS Pristine 38WG Botran 5F Endura 70WG Pristine 38WG Botran 5F Switch 62.5WG Endura 70WG Switch 62.5WG Contans Contans Non-treated control iprodione (Rovral) Rovral) vinclozolin (Ronilan) Ronilan) dicloran (Botran) Botran) boscolid (Endura) Endura) Rate lb a.i./A S. minor S. slerotiorum 1.0 1.0 0.35 4.0 qt prod. 0.4 1.87 0.45 0.45 3.75 0.43 0.35 0.56 4.0 lb prod. 2.0 lb prod. -------- 6.4 9.8 10.0 10.0 10.2 10.8 11.0 11.0 11.0 11.6 11.8 12.4 12.6 16.8 23.2 29.2 21.2 16.6 27.4 27.8 24.6 17.2 19.8 28.2 27.6 37.2 30.0 12.8 18.2 37.8 *each plot contained approx. 55 plants Benefits of biocontrol strategies complement other disease management strategies development of resistance unlikely cost effective few restrictions on use worker and environmental safety development of specialty markets Objectives 20022002-2003 • • • evaluate the efficacy of commercially available biocontrol agents for the control of lettuce drop evaluate the survival of biocontrol agents in the field evaluate the sensitivity of biocontrol agents to Botran, Botran, Rovral, Rovral, and Ronilan 3 120 100 100 40 20 0 80 60 40 20 0 Pla Yuma S. Minor Trial 2003 Yuma S. Sclerotiorum Trial 2003 120 120 100 80 60 40 20 100 80 60 40 20 n rd ua pa nio ilg m so co ld ev it an s ie es pr su nt sh co pla nt tr n ar d pa nio co m re se vit so ilg u ta ns ol hie ld su p pla nts co n ntr ro vr al co ol 0 0 bla nk Tu sa Tr l ic ho de x So ilg ar C om d pa nio Su n pr es ev it 60 R ov ra l C on ta ns nt sh ie ld R oo ts hie ld 80 vr al record incidence of lettuce drop record number and weight of marketable lettuce heads Yuma S. minor trial 2002 120 ro Yuma Biocontrol Trials Yuma S. sclerotiorum trial 2002 Healthy heads/50' bed Evaluate the efficacy of commercially available biocontrol agents for the control of lettuce drop B la nk C on tr ol Sporidesmium sclerotivorum he althy heads/ 50' bed nk bla co n Trichoderma harzianum Companion – Bacillus subtilis RCBD with 4 blocks biocontrol treatments plus one fungicide treatment plus control two trials - high and low density of sclerotiasclerotia- S. minor and S. sclerotiorum two application schedules - prepre-plant application and prepre-plant plus side application healthy heads/50' bed la nk on tr ol R ov ra l C on Pla tan s nt sh ie R ld oo ts hi el d Tu sa Tr l ic ho de x So i lg ar C om d pa Su nio n pr es ev it B Contans - Coniothyrium minitans Soilgard - Gliocladium virens Trichodex, Trichodex, Supresivit, Supresivit, TRI 002 - C Evaluate the efficacy of commercially available biocontrol agents for the control of lettuce drop healthy heads/ 50' bed Evaluate the efficacy of commercially available biocontrol agents for the control of lettuce drop Blank Untreated control Rovral Contans Imperial Valley Biocontrol Trials Holtville S. minor trial 2003 120 healthy heads/50' bed 140 120 100 80 60 40 20 100 80 60 40 20 n pa ni o co m ta ns co n an ts hi el d pl tr ol ro vr al co n bl n co m pa nio ta ns co n pla nt sh ie ld tr ol ro vr al co n an k 0 0 bl an k healthy heads/50' bed Holtville S. sclerotiorum trial 2003 140 4 Blank Untreated control LongLong-term Objective To develop biocontrol strategies for desert winter lettuce production that are compatible with chemical and cultural management strategies Rovral Contans 5