Broomrape (Orobanche spp.) is a root parasite, causing severe damage to vegetable and field crops. Its early in-situ detection and control are crucial, but difficult because of its subsurface development. minirhizotron technology enables the in-situ observation of host-parasite interactions. We studied the factors affecting O. cumana control in sunflower (Helianthus annuus L.) under controlled and field conditions, to optimize its chemical control. We detected the initial underground development of O. cumana on sunflower roots, evaluated the control efficacy of O. cumana with Imazapic studied the relations between O. cumana parasitism at different buried-seed depths, its development, and the efficacy of the chemical control. Orobanche cumana parasitism- attachments and meristem initiation- was observed with the minirhizotron. The number of vital attachments on roots of the chemical treated sunflower plants decreased to zero under both controlled and field growth conditions while new attachments continued to develop in the untreated controls. Broomrape shoot emergence was correlated to growing degree days under both conditions. Excellent O. cumana control was achieved in the herbicide treated sunflower. Control efficacy was affected by attachment depth and density: it was highest in the topmost layer,but decreased with depth and attachment density.