V

Fig 9.1. Historical profile for pest problems in the Sudan Gezira (after Griffiths, 1984).

Tenants

Cotton ha per tenant

Sorghum area

Wheat area

Groundnut area

Fodder area

Cotton area

Bacterial blight

Leaf curl virus

Jassids

American bollworm

Whiteflies

Pesticide applications per year

1925 1945 1965 1985

Fig 9.1. Historical profile for pest problems in the Sudan Gezira (after Griffiths, 1984).

changes that occurred in the area and rotation of crops in the 1950s probably contributed to the increase in American bollworm which led to a subsequent increase in insecticide use. The consequence of this was an increase in whitefly populations (Griffiths, 1984). In addition, cotton production and protection has been influenced by institutional and financial arrangements which affected farmers' incentives to grow good cotton. Through highlighting these changes and associations over time the historical profile provides a structured means of collating

Fig. 9.2. A seasonal profile for olive tree pests in Spain (Claridge and Walton, 1992).

diverse information, brings a range of expertise to bear on a problem, and raises questions to hypotheses relevant to developing solutions (Norton, 1987).

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