Integration of Cultural and Chemical Methods for Management of Broomrape ( Orobanche crenata Forsk.) on Faba bean

Abstract

During the course of this study (2009-2015) a field survey, laboratory and field experiments were conducted. The field survey was performed in 2009/10 to ascertain spread and levels of infestation, in faba bean, of the root parasitic weed Orobancche crenata in an area west of Berber in the River Nile State. The laboratory experiments were undertaken at the Striga Research laboratory at the College of Agricultural Studies (CAS), Sudan University of Science and Technology (SUST) Shambat, Khartoum North, to study the effects of urea and the herbicide imazethapyr on O. crenata germination and radicle extension. The field experiments were undertaken at the parasitic weed enclosure at CAS, to study the effects of imazethapyr alone and in combinations with nitrogen, as urea, on O. crenata incidence and faba bean (Vicia faba) growth and yield. The survey showed a wide distribution of the parasite as over 70% of the fields, surveyed, were infested. Most of the participating farmers (78%) abandoned planting of faba bean to wheat and vegetables. Hand-pulling was the main method of control and was practiced by 46% of the farmers. Chemical control was practiced by only 6%, while the rest of the farmers adopted no control measures. Urea at 20-60 mM, applied during conditioning, reduced germination and radicle extension significantly. Increasing urea to 70 mΜ or more resulted in further reductions. Conditioned O. crenata seeds treated with GR24, a synthetic germination stimulant, and subsequently with urea or conversely with urea and subsequently GR24 displayed inconsistent germination and radicle extension. Conditioned seeds treated with a mix of GR24 and urea displayed significant reductions in both germination and radicle extension. Imazethapyr showed inconsistent effects on O. crenata germination. The herbicide showed inconsistent effects on radicles extension when the seeds were treated with GR24 at 0.I and 1 ppm. However, on germination, seeds treated with GR24 at 10 ppm

showed significant reductions in radicle extension. In the field experiments imazethapyr, irrespective of rates and application time, effected considerable to excellent (23-99%) reductions in Orobanche crenata infestation early in the season. The herbicide at high rate (30 g a.i. fed-1) irrespective of application time was more suppressive to the parasite than at low rate (20 g a.i. fed-1). Nitrogen at 40 kg fed-1 (1N) as urea, irrespective of application time showed considerable suppression of the parasite late in the season. Imazethapyre nitrogen combination was slightly less suppressive than the herbicide alone. Nitrogen, alone, had no effect on number of Orobanche capsules. Imazethapyr at 20 g a.i. fed-1 reduced capsules production considerably (28.3%). However, when combined with nitrogen significant reductions (43.3-50.2%) were achieved. Imazethapyr at 30 g a.i. fed-1, alone, or when followed by nitrogen, irrespective of application time, effected significant reductions (68-85%). Unrestricted O. crenata infestation reduced number of faba bean leaves by (6-21%), height by (1-12%), flowers by (33%), pods by (20-38%), hundred seed weight by (1-5%) and yield by (35-47)%. Nitrogen increased the number of faba bean leaves, flowers, pods, and faba bean height and grain yield by 10-22, 9-41, 32-68, 6-16 and 7-22%, respectively over the infested control. However, it showed non-significant decrease in 100 seed weight. Imazethapyr, at 20 g a.i. fed-1, increased faba bean height, number of leaves, flowers, pods, 100 seed weight and grain yield by 0-29, 0-57, 16, 0-80, 0-7 and 24-72%, over the infected controls. However, when followed by nitrogen the corresponding increments were 5-21, 28-57, 13-110, 54-71, 0 and 41-87%. Imazethapyr, at 30 g a.i. fed-1, alone, increased faba bean height, number of leaves, flowers, pods, 100 seed weight and grain yield by 0-5, 0-17, 10, 29-84, 0-4 and 26-79%, respectively over the infected controls. However, when followed by nitrogen the corresponding increments were 2-17, 2-43, 4-79, 86-120, 0-36 and 63-111%. In conclusion, urea, effectively reduced Orobanche crenata seeds germination and radicle extension. The herbicide effectively suppressed Orobanche emergence, capsules production and increased faba bean grain yield. Nitrogen, alone had inconsistent effects. However, when applied subsequent to the herbicide, it improved treatments efficacy and further increased grain yield.