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 method should be interpreted with great caution in studies with significant amounts of destroyed grains.