The limited area occupied by these trap crops can be treated with a pesticide once pests are drawn to the trap in large enough numbers to reduce the pest populations. In some organic systems, farmers drive over the trap crop with a large vacuum-based implement to physically pull the pests off the plants and out of the field.[36] This system has been recommended for use to help control the lygus bugs in organic strawberry production.[37] Another example of trap crops are nematode resistance white mustard (Sinapis alba) and radish (Raphanus sativus). They can be grown after a main (cereal) crop and trap nematodes, for example the beet cyst nematode[38][39] and Columbian root knot nematode.[40] When grown, nematodes hatch and are attracted to the roots.