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A major concern in potato and onion production worldwide is the sustainability of crop production systems using short-term rotations. Although rotation crops are known to influence soil microbial communities, few long-term field studies have investigated effects of potato and onion crop rotations on soil microflora and soilborne diseases. A long-term trial (10 years) was established in New Zealand in the 2004–05 season to determine changes in soil characteristics, soil biological communities, plant productivity and soilborne diseases resulting from different crop rotations. Six different crop rotation ‘treatments’ were used: three were onion-focused and three were potato-focused. For both the onion- and potato-focused rotations, one treatment was continual monoculture, one was biennial alternating onion and potato (‘conventional’ rotation, common local commercial practice) and one was a 4-year cycle where the onion or potato crops were grown every fourth season with different crops in the intervening seasons (‘sustainable’ rotation). The results of the rotations were evaluated at the end of 2012–13, nine growing seasons after the trial began. Soils from the three potato-focused rotations had similar microbial biomass carbon (C) and nitrogen (N), total C and N, and enzyme activity, but had different microbial activity parameters. Soils from the three onion rotations differed in organic matter content, total C and N, enzyme activity and carbohydrate utilization. The main factor correlated with potato diseases (stem canker, black scurf) and crop yields was the amount ofRhizoctoniainoculum in the soil. Onion yields in 2012–13 were correlated with the severity of pink root during the growing season. Total microbial activity in soil gave better relationships to soilborne disease incidence (Rhizoctonia stem canker of potato or pink root of onion) and to crop yields, than soil chemical parameters (pH, nutrient status, C:N ratio) or other microbiological parameters (microbial biomass, total culturable bacteria and fungi, and microbial diversity). This research has broadened understanding of effects of crop rotations on soil microbial community characteristics, soilborne diseases and crop productivity of potatoes and onions grown in a soil and an area where intensive vegetable production is common. This knowledge will assist growers to increase crop yields and reduce soilborne pathogens in a sustainable manner. Based on the results from this study, intensive potato and onion production should require these crops to be grown within 4-year crop rotations in order to foster sustainable yields and minimize soilborne diseases. [ABSTRACT FROM PUBLISHER]

A field trial was conducted in 2012–2013 at Pukekohe to determine the efficacy of wettable sulphur, applied as a foliar treatment within a reduced insecticide programme, to control tomato-potato psyllid (TPP). Three of the four treatments included wettable sulphur (Kumulus® DF; at 6 kg/ha), either alone or in combination with other insecticides. The remaining treatment was a standard 7 day insecticide spray programme. Spraying for all treatments began at 60% plant emergence on 29 November 2012, and continued until 14 March 2013. The study demonstrated that although sulphur applications may reduce TPP nymph numbers on potato foliage, especially when used in combination with insecticides, sulphur alone is not an adequate TPP management strategy. The field trial results for sulphur-only treatments support previous work suggesting that although sulphur may slow the build-up of TPP populations by deterring egg-laying, the lack of repellence or anti-feeding properties still results in the transmission ofCandidatusLiberibacter solanacearum by TPP. Given the ZC results, it is difficult to draw conclusions from this trial about the efficacy of sulphur/insecticide combinations for TPP management. [ABSTRACT FROM AUTHOR]

A study over two growing seasons evaluated the efficacy and cost effectiveness of azoxystrobin (Amistar® SC), applied at different action thresholds and plant growth stages, on the incidence and severity of common rust of maize grown in the Pukekohe, New Zealand. Azoxystrobin applied as a preventative before disease symptoms appeared, or at the onset of disease symptoms, gave equal or better control than fungicide applications applied at 3% and 6% rust thresholds. However, using a 3% disease threshold up to the tasselling stage to time the application of azoxystrobin, controlled common rust in the more severe rust season (2008–09) and saved fungicide application costs associated with preventative (calendar) or disease-onset applications of azoxystrobin in the less severe rust season (2007–08) when the rust levels did not reach 3% by the tasselling stage. The maize hybrid 34D71 used was classified as moderately susceptible to common rust and, from the research presented here, it appears that although azoxystrobin applications reduced common rust severity, the lack of yield gains suggests that azoxystrobin applications in northern New Zealand may be economic only when growing highly susceptible maize varieties. [ABSTRACT FROM AUTHOR]

Fungicide use in processing (field) tomatoes from 1995 to 2009 on the East Coast of the North Island of New Zealand has been documented using data extracted from growers' annual spray diary records. During this period, 26 different fungicides—some of which are also used as bactericides—were used by growers to control a range of plant diseases. The number of fungicide applications to each crop ranged from 10 to 28, with fewer applications in very dry seasons. Inorganic copper (mainly copper hydroxide), applied to control both bacterial and fungal diseases, was the most commonly used material, followed by chemicals in the dithiocarbamate, chloro-nitrile and pyridinamine groups. These four multi-site ‘protective’ fungicide groups accounted for 90% of all disease-control products used during the 15-year period. Site-specific fungicides (e.g. benzimidazoles, phenylamides, dicarboximides, dimethomorph and strobilurins) were used much less frequently. The exclusive use of fungicides at risk from fungicide resistance development (most commonly the site-specific fungicides) was generally avoided and therefore overall risk of the development of fungicide resistance in processing tomatoes in Hawke's Bay is believed to be low. This study demonstrated that the number of fungicide applications per crop has increased about two-fold since 1995 while, during the same period, insecticide applications decreased. [ABSTRACT FROM AUTHOR]