Orobanche species in Sudan: history, distribution and management

Orobanche species are debilitating root parasitic weeds on several economically important crops. In Sudan three species, O. ramosa, O. cernua and O. minor, were reported as early as 1948. O. crenata was first reported in 2000/2001. Of the four Orobanche species O. ramosa and O. crenata are naturalized and have become pests of economic importance. Tomato (Lycopersicon esculentum Mill.) and potato (Solanum tuberosum L.), the main hosts of O. ramosa, and faba bean (Vicia faba L.), the major host of O. crenata are grown, annually, on 40, 20 and 66 thousand ha, respectively mainly in the alluvial soils of the Nile valley. Mismanagement stemming from lack of awareness of the debilitating effects of the Orobanche species, their biology, invasive nature and means and methods of spread has led to out-break of the parasites. O. ramosa has spread from Rosarious on the Blue Nile and Kosti on the White Nile to Wadi Halfa on the southern borders of Egypt. The highest infestations were, however, reported from the Gezira and Khartoum States causing serious losses on tomato and potato yields. O. crenata was first reported in Merowe governorate in the Northern State in 2000/2001 and subsequently in 2001/2002 in the River Nile State. The parasite is spreading at an escalating rate. Infested area in Merowe governorate increased to about a 1000-fold within 5 years. The number of infestation foci in the River Nile state increased from 1 in 2001/2002 to over 90 in 2005/2006. Pending intensity of infestation, losses of 2-100% in yield of faba bean were reported. No single measure provides effective control and an integrated approach comprising preventive, cultural, biological and chemical methods needs to be adopted. Education is the most important element in control and containment of Orobanche spp. Farmers and policy makers, through training, farmer's field schools, pack stoppings, field visits, lectures, radio and television messages, leaflets, brochures articles in local news papers and a local workshop were made cognizant of the parasites. The importance of starting with clean seeds, restriction of grazing, cleaning of farm equipment and eradication of incipient infestation were stressed. Eradication of O. ramosa, which is widely spread, is impractical. At present control measures comprise hand-pulling and trap cropping. O. crenata, being a recent introduction, is less of a problem than O. ramosa. The O. crenata free area is estimated to be about 87-95% of the total area under the crop. Detection surveys, regulatory and control measures are invoked by the federal ministry of agriculture and local governments to ensure against continual spread of the parasites into new areas. Light and incipient infestations are removed by hand, while heavily infested fields are planted to crops other than faba bean. The herbicides glyphosate and imazethapyr are promising treatments for O. crenata control in faba bean