EFFECT OF PLANTING DATE ON BROOMRAPE (OROBANCHE-CERNUA LOEFL) INFECTIONS IN SUNFLOWER (HELIANTHUS-ANNUUS L)

Field studies were conducted in 1988 and 1989 to determine the phenology and growth of broomrape in sunflower as affected by crop sowing dates. The parasitic weed attachment was observed in sunflower plants with 6-7 leaves; later it was found throughout the vegetative and flowering period of the crop. O. cernua seedlings with shoot development extensive but subterranean were mainly observed at the early heading stage of sunflower. At this stage they were beginning to reduce sunflower plant growth as compared with non-parasitized plants. The emergence of broomrape began at the early flowering stage of the crop and was particularly abundant throughout this and the achene-filling stage. Generally, broomrape infection was much less at the first than at the second or third sunflower sowings, and caused less reduction in yield. The duration of the broomrape emergence period increased as sowing date was delayed. Since sunflower yield was higher at earlier sowing dates, early sowing may be recommended for sunflower crops in broomrape-infested areas under mild mediterranean climates.