There are few examples in which quantitative measures of natural enemy activity have been incorporated into vegetable IPM treatment guidelines. A survey of current vegetable IPM guidelines for NY and CA shows that in almost 40% of cases, the effects of natural enemies on a given pest in a given crop are unknown, while in another 50% of cases, only general conservation practices are urged even though specific natural enemy species are often known to be important sources of mortality. The incorporation of natural enemy thresholds into vegetable IPM faces many of the same challenges seen in other systems, including the development of cost-effective sampling schemes for natural enemy activity, and determining the relationship between enemy activity measures and subsequent pest mortality or crop damage levels. Field vegetable production also faces the additional challenge of the combination of low pest tolerance levels and an open field situation, which has led to a historical reliance on broad-spectrum insecticides to control multiple pest species, which may often have complex ecological interactions with each other and with multiple natural enemy species. These challenges will be illustrated, and how they have been met, within the context of case studies in vegetable IPM. Areas where additional research is needed will be discussed.