Modeling the emergence of North African Knapweed (Centaurea diluta), an increasingly troublesome weed in Spain

Abstract

North African knapweed (Centaurea diluta Aiton) is an annual weed that is widespread in southern Spain and is of increasing concern in dryland cropping systems. Despite its expanding range in Spain, there is limited information on the emergence timing and pattern of this species, which is critical for developing more timely and effective management strategies. Therefore, there is a need to develop simple and reliable models to predict the timing and emergence of this annual weed under dryland conditions. A multi-location field experiment was established across Spain in 2016-2017 to assess the emergence of C. diluta. At each of 11 locations, seeds were sown in the fall, and emergence was recorded. Overall emergence averaged 39% in the first year across all sites and 11% in the second year. In both years, the main emergence flush occurred at beginning of the growing season. The three-parameter Weibull function best described seedling emergence of C. diluta. Emergence models were developed based on thermal time (TT) and hydrothermal time (HTT) and showed high predictability, as evidenced by root mean square error prediction (RMSEP) values of 10.8 and 10.7, respectively. The three cardinal points were established for TT and HHT at 0.5 ºC, 10 ºC and 35 ºC for base, optimal and ceiling temperature, while base water potential was estimated at -0.5MPa.

We would like to thank Cátedra Adama and the Spanish Weed Science Society (SEMh) for providing financial support for this project. We are grateful to the many students and technicians who assisted with field work at the different experimental locations. We would like to thank the Spanish Goverment for partial funding, through project AVA 2019.020 "Advances in Technological Research in Winter Cereals: Genetic Improvement and Sustainable Management" financed with FEDER funds (80%). Also, Joel Torra acknowledges support from the Spanish Ministry of Science, Innovation and Universities (grant Ramon y Cajal RYC2018-023866-I).