Response of tomato transplants to varying soil residual levels of preplant herbicides.

Processing-tomato (Lycopersicon esculentum L.) cultivation in California has transitioned to the use of transplants, subsurface drip irrigation (SDI), and shallow tillage from direct-seeded, flood-irrigated, deep-tillage systems. Observation of stunted tomato plants in fields treated with preplant herbicides suggests that the herbicides may not be disintegrating as rapidly in the newer system. Greenhouse studies were conducted to assess plant response to trifluralin, S-metolachlor, and pendimethalin at soil-residue levels of 0, 0.03, 0.06, 0.12, 0.25, and 0.5 ppm (0, 0.03, 0.06, 0.12, 0.25, and 0.5 mg l-1, respectively; 1 ppm = 1 mg l-1). Plants grown for 45 days after transplanting showed that all three herbicides at levels as low as 0.03 ppm (0.03 mg l-1) reduced shoot and root growth. Therefore, appropriate methods need to be developed to reduce soil carryover effects of these herbicides in tomatoes grown with SDI system. All herbicides resulted in some reduction in shoot and root biomass of the tomato plants at the higher doses (>0.12 ppm) compared to the non-treated plants. Both S-metolachlor and trifluralin caused significant reductions in shoot and root biomass at 0.5 ppm and the potential of the plants to recover from herbicide injury is unknown. Pendimethalin had a lower potential to cause injury than the other two herbicides. Although the effect of shoot and root biomass reduction on fruit yield and quality was not recorded, this study suggests that preplanting soil tests and appropriate management to reduce soil carryover of these herbicides may be necessary in processing tomatoes grown with SDI. [ABSTRACT FROM AUTHOR]