Response of Hemp Broomrape (Orobanche ramosa) Infestation to some Nitrogenous Compounds

Greenhouse pot experiments were conducted to study the effect of various levels of nitrogen, applied as ammonium nitrate (NH 4 NO 3 ) and ammonium sulfate [(NH 4 ) 2 SO 4 ], on hemp broomrape ( Orobanche ramosa L.) infestation on tobacco ( Nicotiana tabacum L. ‘Jordan 1’) and tomato ( Lycopersicon esculentum Mill. ‘Caludia Raf’). Infestation of tobacco and tomato by hemp broomrape was drastically reduced as higher levels of both fertilizers were applied. However, the dry weights of roots and shoots of both crop plants, as well as tomato yield, were reduced when NH 4 NO 3 was applied at 50 g/pot, and when (NH 4 ) 2 SO 4 was applied at higher than 60 g/pot. In a separate pot experiment in the field, hemp broomrape infestation on tomato was drastically reduced, and tomato shoot dry weight, as well as tomato yield, were increased when (NH 4 ) 2 SO 4 was applied at higher than 40 g/pot as 20-g increments repeated at 10-day intervals compared to those of the control.