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Crop multi-model ensembles (MME) have proven to be effective in increasing the accuracy of simulations in modelling experiments. However, the ability of MME to capture crop responses to changes in sowing dates and densities has not yet been investigated. These management interventions are some of the main levers for adapting cropping systems to climate change. Here, we explore the performance of a MME of 29 wheat crop models to predict the effect of changing sowing dates and rates on yield and yield components, on two sites located in a high-yielding environment in New Zealand. The experiment was conducted for 6 years and provided 50 combinations of sowing date, sowing density and growing season. We show that the MME simulates seasonal growth of wheat well under standard sowing conditions, but fails under early sowing and high sowing rates. The comparison between observed and simulated in-season fraction of intercepted photosynthetically active radiation (FIPAR) for early sown wheat shows that the MME does not capture the decrease of crop above ground biomass during winter months due to senescence. Models need to better account for tiller competition for light, nutrients, and water during vegetative growth, and early tiller senescence and tiller mortality, which are exacerbated by early sowing, high sowing densities, and warmer winter temperatures. [ABSTRACT FROM AUTHOR]

Rust diseases are serious threats to New Zealand cereal crops. Beside the use of fungicides, resistant varieties are an important option for managing these diseases. Changes in rust pathotypes commonly occur due to mutations in existing populations or exotic incursions. Information on these changes is the basis of gene-based disease management. Rust-infected leaves were collected from cereal crops from 2012 to 2015. The pathotypes of these and some historic samples were determined in glasshouse studies, using specific differential host sets. Eight pathotypes of Puccinia triticina (Pt, causal agent of wheat leaf rust), five of P. striiformis f. sp. tritici (Pst, causal agent of wheat stripe rust) and two of P. hordei (Ph, causal agent of barley leaf rust) were identified. The Pst 'WA' pathotype was most frequently found. Wheat varieties 'Empress' and 'Torch', previously resistant to Pt, were found to be susceptible to leaf rust for the first time. The 'WA' pathotype of Pst is likely to have arrived in New Zealand from Australia, and is now widespread. The two Pt pathotypes could have overcome resistance gene Lr24 in 'Empress' and 'Torch'. [ABSTRACT FROM AUTHOR]