Soil solarisation can provide control of many soil-borne diseases, nematodes, and weeds. Preventing weeds from producing seed helps reduce weed populations in subsequent crops; this also applies to areas adjacent to the cropped fields. A soil cap (5 to 10 cm mound of soil) over the seedline at planting can reduce the first flush of weeds competing with the crop seedlings. The cap is removed just after tomato seedlings germinate, but before rapid elongation of the hypocotyls. This mound also reduces soil moisture loss and emergence problems that result from soil crusting after periods of rainfall, and is formed by disks or other implements.
When tomato seedlings are about 10 cm tall, cultivation can create a dry layer of soil (dry mulch) on the seedline to prevent weed seeds from germinating and to smother small weeds that have already emerged. Flaming is also used for weed control in large-scale commercial tomato production.
- Crop rotation can effectively reduce difficult weed problems by altering the environmental conditions that favour a particular weed species or by permitting the use of alternative methods to control these weeds. Lucerne is a good choice for a rotational crop because its frequent cutting cycle reduces many weeds. Maize is also used in rotations with tomato as it is not a host to tomato diseases and weeds can be controlled in this crop.