Weed problem appears to be the most deleterious factor causing between 25 and 60% reduction in potential yield of cowpea. Field trials were therefore conducted to study the effect of inter-row spacing and period of weed interference on growth and yield of cowpea (Vigna unguiculata (L) Walp) at the Teaching and Research Farm of the Federal University of Agriculture, Abeokuta (07° 15′; 03° 25′ E) in South Western Nigeria during the early and late wet seasons of 2009. The experiment consisted of eight main plots of weed interference which included initial weed removal for 3, 6, 9, and 12 weeks after sowing (WAS) and subsequently weed -infested until harvest as well as initial weed infestation for corresponding periods and thereafter kept weed free until harvest. There were also sub-plot treatments of three inter-row spacing of 60, 75, and 90 cm. All treatments in different combinations were laid out in a split-plot design with three replications. In both trials, the use of inter-row spacing of 60 cm resulted in significant reduction in weed growth as evident in lower weed dry matter production and subsequent higher cowpea pod and grain yields than those of 75 and 90 cm inter-row spacing. Initial weed infestation of up to 3 WAS did not have any adverse effect on crop growth and cowpea grain yields provided the weeds were subsequently removed. On the other hand, cowpea grain yield loss was not significantly averted by keeping the crop weed free for only 3 WAS without subsequent weed removal. In this study, initial weed-infestation for 6 WAS and beyond significantly depressed various crop growth parameter and cowpea grain yield compared with the crop kept weed free throughout its life cycle. In order to obtain optimum yields similar to that of the weed free cowpea field, it was required to keep the crop weed free for 6 WAS and beyond. However, frequent weeding beyond 9 weeks after sowing did not improve cowpea yield significantly and as a matter of fact it may even result in reduction of cowpea grain yield due to mechanical damage of hoe weeding. The practical implication of this finding is that early weeding starting from 3 WAS is very crucial for cowpea production while the critical period of weed removal for optimum yield in cowpea is between 3 and 9 WAS in the forest-savannah transitional zone of south Western Nigeria.

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can also be described as tolerance, in that high grain yields are The parasitic witchweed, Striga hermonthica (Del.) Benth, is the greatest attained in the presence of reduced host plant damage by Striga

The germination of giant witchweed [Striga hermonthica (Del.) Benth], a noxious root parasite of many cereal crops, is stimulated by exudates from the roots of both host and non‐host trap plants. Forty genotypes of cotton (Gossypium hirsutum L. and G. barbadense L.), a trap crop, were screened in the laboratory, using the cut‐root technique, to investigate the variability among these genotypes for their ability to stimulate suicidal germination of S. hermonthica and to determine the inheritance of the trait. The genotypes exhibited significant differences for the trait. S. hermonthica seed germination percentages ranged from 13.3 to 50.0% for the cotton genotypes compared with 47.3% for the susceptible sorghum [Sorghum bicolor L. Moench)] cultivar CK60B. Three cotton genotypes were selected based on their S. hermonthica seed germination stimulation and used as parents in crosses of the combination low × high S. hermonthica seed germination stimulation. The F1s, F2s, and parents of the crosses, RASA(78)11b × ‘SAMCOT‐10’ and RASA(78)11b x TX‐CABS‐1‐83 were evaluated in separate experiments in batches of 12 entries. Broadsense heritability estimates for the trait ranged from 71.8 to 78.5%. This was reflected in the discrete frequency distribution of the F2 populations into two classes of high and low S. hermonthica seed germination stimulation, fitting a classical 3:1 phenotypic ratio. These results suggest that S. hermonthica seed germination stimulation by cotton is a qualitatively inherited trait, and that the gene controlling this trait is monogenic and simply inherited, with high S. hermonthica seed germination stimulation dominant over low S. hermonthica seed germination stimulation. It should be possible to select and breed cotton genotypes that produce highly active germination stimulants in large amounts, while maintaining or improving other agronomic attributes.

Field trials were conducted in the dry (Experiment I) and wet (Experiment II) seasons of 1997 at Samaru (11°11' N, 7°38' E, 686 m above sea level) in the northern Guinea Savanna ecological zone of Nigeria to study the effects of nitrogen rates on the reaction of upland rice (Oryza sativa L.) varieties to Striga hermonthica (Del.) Benth. The results indicate that FARO 48, a variety normally susceptible to Striga hermonthica, exhibited resistance. FARO 11 exhibited tolerance, while FARO 38, FARO 46 and FARO 45 exhibited susceptibility. The application of 90 and 120 kg N/ha delayed and reduced Striga emergence on the crop, induced a low crop reaction score and produced grain yields that were the maximum or significantly higher than the least. No significant differences in Striga infestation were observed between nitrogen rates of 30-120 kg N/ha. The significant interaction between upland rice varieties and nitrogen rates indicates that the susceptible varieties require higher rates of nitrogen to ameliorate the effect of Striga compared with the resistant varieties.