Bactericera (Paratrioza) cockerelli (Šulc) (Hemiptera: Triozidae) is a native American psyllid species that was first reported in New Zealand in 2006. In 2008, the insect was associated with a new-to-science pathogen, Candidatus Liberibacter solanacearum (syn. ‘Ca. L. psyllaurous’) (Rhizobiales: Rhizobiaceae). This pathogen is the putative causal agent of zebra chip disease of potato tubers, which makes them unsuitable for processing, causes disease in seed tubers, and is perceived to affect the taste of fresh market potatoes, as well as their internal appearance. The insect/pathogen complex is also an important economic pest of other solanaceous crops, including tomato, capsicum, tamarillo, and eggplant. Here, we review the literature on the phloem-limited pathogen and focus on the integrated management of its insect vector in New Zealand. Comparisons with other regions of the world are made where appropriate. We review the current understanding and paradigms of insect-mediated transmission of plant pathogens, an increasingly important area as more Liberibacter species are discovered world-wide. Knowledge gaps are identified and recommendations made for future research aimed at defining the fundamental biological parameters underpinning the epidemiology and pathology of the disease caused by Ca. L. solanacearum in potato.

Co-innovation can be effective for complex challenges – involving interactions amongst multiple stakeholders, viewpoints, perceptions, practices and interests across programmes, sectors and national systems. Approaches to challenges in the primary sector have tended to be linear, where tools and outputs are developed by a few, mostly scientists/researchers, and then extended to stakeholders. A co-innovation approach first deciphers and delineates the biophysical, societal, regulatory, policy, economic and environmental drivers, constraints and controls influencing these challenges at multiple levels. Second, stakeholder interactions and perspectives can inform and change the focus as well as help in co-developing solutions to deliver agreed outcomes. However, there is limited systematic and comparative research on how co-innovation works out in different projects. Here we analyse the results of applying a co-innovation approach to five research projects in the New Zealand primary sector. The projects varied in depth and breadth of stakeholder engagement, availability of ready-made solutions and prevalence of interests and conflicts. The projects show how and why co-innovation approaches in some cases contributed to a shared understanding of complex problems. Our results confirm the context specificity of co-innovation practices.

Disease dynamics of Cercospora leaf spot (CLS) of sugar beet was analyzed at two hierarchical scales: as vertical profiles within individual plants and in relation to disease on neighboring plants. The relative contribution of different leaf layers to increase in CLS was analyzed using a simple continuous-time model. The model was fitted to data from two field trials in the Netherlands: one in an area with a long history of CLS, the other in an area where CLS has only recently established; in each case these were unsprayed and twice-sprayed treatments. There were differences in the relative contribution of different leaf layers to disease increase on the target leaf layer according to the CLS history and whether the plants were sprayed or unsprayed. In both field trials, parameter estimates giving the relative contribution of the target leaf layer to disease increase at that leaf layer were higher than those for the lower leaf layer. On only a few occasions the contribution of an upper leaf layer to disease increase at the target leaf layer was significant. Thus, CLS increase at the target leaf layer was determined mainly by disease severity at that leaf layer and to a lesser extent by disease at the lower leaf layer. Our continuous-time model was also used to analyze CLS increase on an individual sugar beet plant in relation to its own and its neighbor's level of disease in field trials at five locations in the two CLS areas over two years. In all field trials, the contribution of the target plant itself to disease increase (auto-infection) was larger than that of its neighboring plants (allo-infection). The overall analysis in the two CLS areas also indicated a larger contribution of the target plant to its disease increase than of neighboring plants, and this pattern was also apparent in a pooled analysis across all sites. Thus, CLS increase on a sugar beet plant was mainly determined by the disease severity on that plant and to a lesser extent by its within-row neighboring plants.