Rapid assessment methods for small farm storage surveys

Farm surveys are often the first step taken in identifying storage problems. As time and money for such work are generally scarce, it is important to be able to make the best use of them to get the information needed. This paper describes some of the specific techniques and experience developed by the Ghana MoFA/UK ODA Larger Grain Borer Project for rapid storage surveys on small-scale farms. It is argued that the following factors can critically contribute to producing more timely and relevant results: • formulation of specific survey objectives which focus on gathering data needed for decision-making. • use of a range of techniques to meet these objectives, including secondary data and key informants, informal surveys, case studies and participatory meetings. • avoidance of unwitting sampling bias, using rapid techniques such as transect village walks to select farmers, along with careful timing of field visits. • methods of sample analysis which can be used in the field, rather than the lab. Field analysis has many benefits including cost, speed, potential for increased sampling, and most importantly the greater participation of farmers and field staff in the analysis and interpretation of results. • use of rapid and flexible techniques of analysis and presentation, in particular mapping. Practical examples of each of these are given

The modified count and weigh method: An improved procedure for assessing weight loss in stored maize cobs

This paper describes a modification of the well-known count and weigh (gravimetric) method for assessing losses due to insect pests in stored maize cobs. The modification involves counting the destroyed grains on each cob and using an adjusted calculation. Data are presented to show that the precision of the modified method is similar to that of the conventional count and weigh method. No systematic bias was detected with the modified method, in contrast to the conventional method which is shown to underestimate true weight loss by up to half. The main justification given for the use of the modified method is that the conventional method underestimates loss to an unpredictable extent, depending on the degree to which pest-damaged grains retain a separate, countable identity. For example, it is shown that the degree to which the conventional method underestimated loss was much greater for a floury, small-grained variety, in which many insect-damaged grains were reduced to powder, than for a large- grained variety in which most damaged grains retained their identity. This implies that comparisons of weight losses based on the conventional med1od should be interpreted with great caution in studies with significant amounts of destroyed grains