Competition between Avena sterilis ssp. sterilis and wheat in South Western Spain

Avena sterilis spp. sterilis has different growth and demographic characteristics than other weedy taxa of Avena . Preliminary studies have shown that wheat yield losses caused by this species were larger than those produced by the spp. ludoviciana . These losses were estimated experimentally in 19 wheat fields distributed throughout western Andalusia. The relationship between A. sterilis spp. sterilis density per square meter and the wheat grain weight was estimated using several simple models. The results obtained confirm that this weed species was tremendously competitive even at low densities, obtaining wheat yield losses up to 70 kg ha –1 panicle –1 m –2 . The potential crop yield of the field was considered as an important factor to estimate the yield losses. A relationship between the expected weed-free yield of wheat and the yield loss per panicle of A. sterilis spp. sterilis was used to determine the economic threshold. This threshold ranged from 4 to 81 panicles m –2 depending on the potential yield of each field. Farmers with high potential yields (> 6,000 kg ha –1 ) should treat their fields if A. sterilis density is above 10 panicles m –2 . Farmers with low potential yields (< 3,000 kg ha –1 ) should not applied any herbicide control to their fields whatever the infestation density. And if the potential yields are between 3,000 and 6,000 kg ha –1 they should estimate the economic threshold value from the exponential equation described in this work.