PREDICTING YIELD LOSS DUE TO INTERFERENCE FROM 2 WEED SPECIES USING EARLY OBSERVATIONS OF RELATIVE WEED LEAF-AREA

Experiments were conducted on linseed (Linum usitatissimum L.) and aut umn-sown field bean (Vicia Saba L.) to test how well the relative leaf area-based yield loss prediction model of Kropff & Spitters could est imate yield loss due to interference from Stellaria Media L. (common c hickweed) or barley (Hordeum vulgare L.) alone or a combination of bot h S. media and barley. Damage coefficients were calculated for all com parisons. Generally, the model provided a better estimate of yield los s due to interference from barley than from S. media because of both t he variability in crop yield response stemming from S. media's plastic ity and the generally minor crop yield response to S. media interferen ce. The addition to the model of a parameter accounting for asymptotic yield loss was, generally, not warranted for either S. media or barle y in the single-weed species data sets. When both S. media and barley were present as weed species in the crop, the model that fitted the da ta best for six out of 10 data sets was the one in which a separate da mage coefficient was included for both species. There was no evidence that the presence of S. media influenced damage coefficient values for barley. However, in the presence of barley a parameter accounting for asymptotic yield loss was warranted for S. media in the two-weed spec ies model. The combination of the addition of this parameter and the p resence of barley affected the values of the damage coefficients for S . media in the two-weed species compared with the single-weed species models. Consequently, it was shown for these two weed species that two -weed species yield loss prediction models parameterized using data fr om single-weed species experiments generally resulted in different est imates of yield loss in comparison with models parameterized using dat a from two-weed species experiments.