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’.

Crop multi-model ensembles (MME) have proven to be effective in increasing the accuracy of simulations in modelling experiments. However, the ability of a MME to capture crop response 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.

Pyrenophora triticirepentis the cause of tan spot of wheat was first recorded in New Zealand in 1979 but only on wheat seed However this pathogen has recently been recorded as causing possible yield losses in isolated crops A small plot trial set up in a central Canterbury crop of cv Saracen tested several fungicides alone or in mixtures Control was not entirely effective since tan spot infection was well established when the first applications were made at GS33 (third node detectible) Nevertheless two triazoles (propiconazole and prothioconazole) and three SDHI fungicides (isopyrazam bixafen plus prothioconazole and fluxapyroxad plus epoxiconazole) all gave similar levels of control either when applied alone or in mixtures Two triazoles (epoxiconazole and difenoconazole) were less effective alone while addition of strobilurin (pyraclostrobin) to mixtures gave little extra control Several treatments showed significant increases in green leaf retention and final grain yield The life cycle of the pathogen dictates that management of the overwintering inoculum in stubble is a probable essential step in control of the disease

In the 2012-13 and 2013-14 seasons septoria tritici blotch (STB) caused by the fungal pathogen Zymoseptoria tritici was poorly controlled in autumn sown wheat in Canterbury. In 2014-15, a low disease pressure season, three trials were conducted to define the protectant and curative properties of two applications of triazole demethylation inhibitor inhibitor (DMI) and succinate dehydrogenase inhibitor (SDHI) fungicides for the control of STB at growth stage 31 and 39 on two cultivars of autumn sown wheat. The protectant activity of triazole and SDHI fungicides was more effective on the flag leaf than the curative activity on leaf two. The addition of an SDHI to a 75% fixed rate of triazole was more effective at controlling STB infection than triazoles alone. The addition of SDHI fungicides also significantly increased yield. The highest mean yields were achieved with the addition of a third application at GS65.

Tan spot of wheat is caused by the fungus Pyrenophora triticirepentis (Ptr) with reported incidence in New Zealand increasing in recent years Lesions characteristic of Ptr infection being oval tan spots surrounded by a chlorotic halo were observed on wheat leaves in 15 different wheat paddocks throughout the South Island in the 201314 season Fungal isolates recovered from these lesions on potato dextrose agar produced greygreen fluffy mycelium characteristic of Ptr Speciesspecific PCR using published primers (PtrUniqueF2/ PtrUniqueR2) generated a PCR product of 490 bp diagnostic of Ptr Sequencing of the rDNA and 946;tubulin gene regions confirmed the identification Ptr was found to be widely distributed throughout the wheat growing areas in the South Island from Southland to North Canterbury A postharvest farmer questionnaire was also undertaken Questionnaire answers revealed that continuous sowing of untreated wheat seed conservative tillage and low rate applications of fungicides may have exacerbated the severity of tan spot outbreaks during the 201314 season Further work to identify susceptible wheat cultivars and sensitivity to fungicides is currently under way