Evaluation of Chemicals and Application Methods for Control of Bacterial Wilt of Tomato Transplants

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Abstract
Chloropicrin, whether covered with a polyethylene film or sealed with water, was the only soil treatment chemical of 8 evaluated that provided significant full-season control of Pseudomonas solanacearum which causes bacterial wilt of tomato [Lycopersicon esculentum]. A methyl bromide-chloropicrin mixture (67-33%) and DD-MENCS (a mixture of methyl isothiocyanate, dichlopropane and dichloropropene) retarded wilt development less effectively than chloropicrin but more effectively than methyl bromide. Methyl bromide gave good control only until midseason. Metham gave poor to moderate early-season control and was more effective when injected than when applied as a drench or incorporated. Potassium N-hydroxymethyl-N-methyldithiocarbamate and sodium azide provided limited early-season control. Hexachlorophene and formaldehyde were ineffective. Chloropicrin and methyl bromide applied at 1/2, full, or twice the recommended rates (chloropicrin 326 l/ha, and methyl bromide 490 kg/ha) under optimum conditions, were highly effective in reducing high populations of P. solanacearum in artificially infested soils in greenhouse tests. High-populations of P. solanacearum are necessary for bacterial wilt development, low residual pathogen populations remaining after chemical treatment rapidly increase to disease threshold levels in the presence of tomato roots. Chloropicrin is the most promising chemical for reducing bacterial populations in fields used for transplant production.

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