Which of the following problem has the least effect on agricultural productivity in West Africa?

Analyze the question: We are asked which problem has the least effect on agricultural productivity in West Africa. We need to compare how strongly each factor reduces farm output.

Concept: Agricultural productivity depends on natural factors (weather, pests), human factors (skills, education, labour), and capital and land. In West Africa, farming is mostly rain-fed and small-scale, so it is very sensitive to the environment and to farmers' knowledge.

Evaluating each option:

• A. Incidence of pests and diseases: Pests such as locusts, quelea birds, and cocoa swollen shoot disease can destroy crops and livestock. This has a major effect on output.
• B. Unfavourable weather conditions: Droughts, floods, and irregular rainfall strongly affect yields, especially because irrigation is limited. This has a major effect.
• C. Urban-rural migration: This phrase describes movement from towns to villages. That is the opposite of the usual problem, rural-urban migration, which drains farms of young labour. Urban-rural migration would actually add labour to rural areas, so it would not reduce agricultural productivity. It is the least harmful.
• D. Illiteracy: It limits the adoption of modern techniques, improved seeds, fertilizers, and good record keeping. This has a significant effect.

Conclusion: Options A, B, and D all clearly lower productivity. Urban-rural migration does not, so it has the least negative effect.

Tip: Read the direction of migration words carefully. Rural-urban migration hurts agriculture (farm labour leaves), while urban-rural migration does the reverse. In "least effect" questions, look for the option that doesn't actually fit the problem being described.