Persistence of Fungicides in Tomato following Application of Metalaxyl-Mancozeb Combined Formulation

Persistence of metalaxyl and mancozeb (MZ) was studied under field conditions in tomato and in soil. Foliage deposited comparatively higher initial residues of fungicides than fruits following foliar applications. Metalaxyl residues dissipated at higher rate in foliage (t1/2 3.13 - 4.14 d) as compared to fruits (t1/2 7.82 - 8.75 d). A reverse trend of dissipation was observed for mancozeb. The half-life values varied from 13.87 -13.56 d on foliage and 5.23 - 6.95 d on fruits. Maximum concentration of ETU was recovered on the zero day of second spray compared to other days indicating the carry over of ETU residues metabolised from mancozeb of the first spray application. ETU in foliage persisted beyond 40 days. However, fruits after 40 days were devoid of any detectable residues. Waiting period was worked out to be 18 d after the last spray application of metalaxyl-MZ. The half-life values were also less than 10 d for metalaxyl, while 7 d for mancozeb. The residues of both the fungicides received by the soil from foliar applications to tomato crop did not persist beyond 30 days.