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, knowledge of 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 to 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 the beginning of the growing season. A 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 values of 10.8 and 10.7, respectively. Three cardinal points were established for TT and HHT at 0.5, 10, and 35 C for base, optimal, and ceiling temperatures, respectively, while base water potential was estimated at −0.5 MPa.

Modeling emergence of sterile oat (Avena sterilis ssp. ludoviciana) under semiarid conditions

“…However, substantial differences were found for T o and T c , which were lower than those established in growth chamber experiments by Fernández-Quintanilla et al (1990) and by Üremİs and Uygur (1999), which set them at 10 and 30 C, respectively. On the other hand, with a Ψ b of −0.2 MPa A. sterilis showed higher dependence on soil moisture than other winter weeds, such as ripgut brome (Bromus diandrus Roth) (−1.3 MPa) or C. diluta (−0.5 MPa) (García et al 2013;Sousa-Ortega et al 2020b). Moreover, the established Ψ b in the new model is considerably high compared with that obtained by Fernández-Quintanilla et al (1990), who established it at −1.2 MPa.…”

“…344 Sousa-Ortega et al: Avena sterilis emergence emergence in the first season was lower than for two other species that are of concern in wheat fields in Spain, rigid ryegrass (Lolium rigidum Gaudin; 58%) and North African knapweed (Centaurea diluta Aiton; 39%) (Sousa-Ortega et al 2020a, 2020b. The longer seed dormancy of A. sterilis, which can reach up to 5 yr (Bajwa et al 2017), might explain this result.…”

Monitoring the Spatial Variability of Knapweed (Centaurea diluta Aiton) in Wheat Crops Using Geostatistics and UAV Imagery: Probability Maps for Risk Assessment in Site-Specific Control

“…In addition, the late-season spatial distributions maps within a field may also have other uses, e.g., they could be of benefit to prevent the spread of weeds to clean areas, which is particularly relevant for invasions of new weed species or emerging weeds that threaten an area, thus, helping the development of SSWM strategies. The current restrictions on the number and use of herbicides in cropping systems as well as the tillage frequency in European Union legislation have made it more difficult to control troublesome weeds and have led to an increase in the occurrence of lesser-known weeds, such as Centaurea diluta Aiton (common name: knapweed) [53], which is an emerging troublesome annual weed that has spread into southern Spain in recent years and is of increasing concern to farmers in the dryland cropping systems [54]. This taxon belongs to the complex genus Centaurea L. (Asteraceae), a taxonomically complex group centered in the Mediterranean region [55].…”

“…Centaurea L. (Asteraceae) includes species, such as C. calcitrapa L., C. iberica Trevir.ex Spreng, C. cyanus L., and C. solstitialis L. [56,57], which are considered troublesome weeds, whereas others, including C. diffusa Lam. and C. melitensis L., are of minor agronomic importance [53]. Most species are distributed in the eastern Mediterranean region and the Irano-Turanian regions, although some species are exclusive to the western Mediterranean region and others have a wider distribution.…”

“…Most species are distributed in the eastern Mediterranean region and the Irano-Turanian regions, although some species are exclusive to the western Mediterranean region and others have a wider distribution. A total of 94 Centaurea species have been described in the Iberian Peninsula including the increasingly troublesome annual herb, C. diluta [53].…”