Weeds in sweet corn reduce the yield and are economically more harmful than other pests. The aim of this study was to evaluate the effects of mechanical weed control and efficacy of pre- and postemergence applied herbicides in sweet corn, and their influence on weed control expressed by various indices, corncob yield and net return. Field studies were carried out with preemergence thiencarbazone-methyl + isoxaflutole (at 29.7 + 74.3 g · ha ^–1), postemergence S-metolachlor + terbuthylazine (937.5 + 562.5 g · ha ^–1), mesotrione + terbuthylazine (100 + 652 g · ha ^–1), terbuthylazine + mesotrione + S-metolachlor (656.3 + + 131.3 + 1093.8 g · ha ^–1), weed free (WF, hand weeding), and mechanical weeding (MW, hoeing) to assess weed control, corncob yield and net return. Variability in potential yield losses was observed between years due to weather conditions at the level of 30 to even 93%. Hand weeding was the most effective, but it is expensive and needs is labour consuming, unlike mechanical weeding which was the cheapest but simultaneously the least effective. Among pre- and postemergence applied herbicides, a mixture of terbuthylazine + mesotrione + S-metolachlor was the most efficacious weed control treatment. It gave high corncob yield and economic net return.

The trials conducted with selected chemical and biological insecticides in 1998-2000 showed the highest effectiveness of Karate Zeon 100 CS (lambda-cyhalotrine) in European corn borer (ECB) larvae control in sweet corn. The efficacy of biological insecticides containing Bacillus thuringiensis ssp. kurstaki: Biobit 3.2 WP and Lepinox WDG was very variable between the years. Reasons for insufficient efficacy of these products are discussed. The most appropriate time for the application of a chemical insecticide against ECB larvae are plant developmental stages since the beginning of pollen shedding to full blooming (63–67 BBCH scale). The efficacy of treatment was the highest at that time.

In the climatic conditions of Lower Silesia, Poland the European corn borer lays eggs on sweet corn during 3-5 week period between the 3rd decade of June and the 2nd decade ofAugust. The eggs are laid on leaves L1 to LS ofmain and lateral stems of the plants. Caterpillars start to hatch at the beginning ofJuly, but in 1998-2000 a massive hatching was observed only in the 2nd and in the 3rd decade ofJuly, whereas in 2001 - in the 3rd decade of this month and in the l st decade of August. Larvae are capable of migrating between plant rows on the soil surface, which was observed in 1998-2000 from the end ofJuly till the end of October. Most caterpillars migrated in the 2nd and in the 3rd decade of August and in the first days of September. The cob damage by caterpillars ranged between 31 and 46%. Delayed harvest caused a substantial increase in damage.