Methods to measure and study weeds

To link their different perspectives on weeds, farmers, extensionists, and researchers need complementary methods to observe and quantify weed species composition, abundance, and distribution. Few would disagree that better quantification of weeds should lead to better management. Cousens & Mortimer (1995, pp. 291-2) suggested that observations should have enough precision to estimate current weed levels and predict trends. Similarly, Firbank (1993) proposed that weed monitoring should capture differences in order of magnitude. Hamilton (1995, pp. 101-4), in his study of adult learning methods with Australian grain farmers, concluded that observation methods should place less emphasis on high accuracy. He suggested that observation should facilitate group analysis of different situations by establishing relative magnitudes. With this type of observation, farmers more readily extrapolated results to other fields or farms.

Research on methods for field level scouting in weed science has concentrated on the decision to apply post-emergent herbicides (Marshall, 1988;

Total weed cover (%)

<5%

5-25 %

25-50 %

>50 %

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