Integrated pest management of nematodes in sweetpotatoes (PW17001)

Surveys have shown that root-knot nematodes (Meloidogyne spp.) are still the most common nematode pests on sweetpotato farms. Reniform nematodes (Rotylenchulus reniformis) are also present in some warmer production soils. A new potentially serious pest to sweetpotato production, Guava root-knot nematode (Meloidogyne enterolobii), has been identified in two regions of Queensland. A pest alert has been produced and sent to all growers with the assistance of Australian Sweetpotato Growers Inc. (ASPG).

The intensive survey is ongoing throughout the major Australian production regions. Nematodes, both plant parasitic and free living, are being monitored in selected on-farm blocks over time. This intensive survey will continue for the life of the project to understand how on-farm practices influence nematode populations. Diagnostic sampling is also available for growers who want adhoc information about nematode numbers in particular blocks.

Long term farming system trials have continued. The third planting of the intensive trial has shown that treatments with added organic matter produced heavier marketable roots than other treatments. The fourth sweetpotato crop in the series has been planted. In the extensive trial, the crop rotations successfully reduced root-knot nematodes but were not as successful in reducing reniform nematode numbers. The third crop in this trial series has also been planted.

A nematicide trial at the Bundaberg Research Facility has also been established, along with pot trials to identify root damage caused by root-knot and reniform nematodes. In addition, a review has been undertaken to identify herbicides that the industry may wish to study for weed control on Australian farms.

A field walk was conducted in Bundaberg in October 2021, providing growers with the latest updates on the long-term trial, cover crop screening for RKN resistance, herbicide plant back experiments and nematicide trials. Details of the field trials and project updates can be accessed via the members only page on the Australian Sweetpotato Growers (ASPG) website

Intensive maintenance and cover crop rotations continue in both of the BRF long-term trials along with a range of soil sampling. Results from the second commercial harvest of the Intensive trial block showed that the nematicide treated blocks produced a higher number of roots per treatment, but the organic amended plots had a higher root weight per treatment. The control plots had a significantly higher incidence of pimpling that all other treatments.

The third commercial sweetpotato harvest of the intensive trial will commence in March 2022. Harvest of the long-term pot trial to investigate RKN damage to two commercial sweetpotato cultivars is also scheduled for the March.

Intensive monitoring throughout the major Australian production regions is ongoing to better understand how on-farm practices influence nematode populations (both plant parasitic and free living).

This reporting period saw several important milestones reached in the Bundaberg Long Term Trial, including harvest of the second commercial sweetpotato intensive trial and continued cover cropping regime in the extensive trial.

A range of soil sampling continued for nematode surveillance screening, physical soil properties, microarthropods and nematode trapping fungi (NTF). Results from the first commercial harvest saw promising data in the intensive block, with a significantly a lower incidence of root-knot nematode and skin lesions in the organic matter treatments.

Follow-on testing of grower sites, selected from the intensive survey, is ongoing and will continue for the life of the project to understand how on-farm practices influence nematode populations. Diagnostic sampling also continued for growers wanting ad hoc information about nematode numbers in particular blocks.

An on-farm nematicide trial was implemented in partnership with Mitchell Feint of AgPD, with applications started and the sweetpotato crop established using variety Orleans. Monthly soil samples are being collected and analysed for nematodes, microarthropods and NTF.

Host range/pathogenicity trials are ongoing, and the team completed:

• An assessment and report on glucosinolate levels in the cover crop demonstration trial
• Two herbicide experiment reports
• An updated summary of cover crop resistance trials
• A report on microarthropod and NTF populations and physical soil properties in the Bundaberg Long Term Trial.

A project update was delivered to Australian Sweetpotato Growers Association (APSG) members in June 2021. A field day scheduled at the Bundaberg Research Facility in August 2021 was postponed due to COVID-19 restrictions, with plans to reschedule at a later date.

As growers were unable to attend a face-to-face field day, project reports and updates were made available on the Members Portal of the ASPG website. As further results become available, these will be shared with growers and added to the cover crop resistance list.

ACT NOW

Visit the Members Portal of the Australian Sweetpotato Growers Association website to access information about this project and its outputs.

Since the last project update, on-farm surveys recommenced with the relaxation of COVID-19 restrictions. Due to long-running drought conditions over most areas, nematode numbers continued to be low.

The long-term farming systems trial in Bundaberg continued, with a second commercial sweetpotato crop planted in the intensive block. The previous rotation crop (Jumbo sorghum) was incorporated, with organic amendments applied and incorporated at bed formation. A second cover crop in the extensive trial (preformed beds) was mulched off, with the block to be planted to signal grass next.

Soil sampling to assess nematode populations, physical properties and biological activity continues throughout the long-term trial, pre-plant at the nematicide trial site, and future cover crop demonstration sites. A suitable site in Bundaberg was identified for nematicide trials, with plans underway and planting set for March 2021.

Several host range pot trials continue to evaluate potential cover crops for nematode resistance or susceptibility. Pathogenicity pot trials are also ongoing, evaluating commercial sweetpotato cultivars to gauge nematode infection susceptibility / resistance ratings.

A second herbicide trial is underway to investigate any ‘plant back’ effects of pre-plant herbicide treatments on sweetpotatoes post planting. A second factsheet Environment and herbicide performance was completed and distributed to growers.

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Read this herbicide fact sheet:

Environment and herbicide performance.

Since the February 2020 update, Covid-19 travel restrictions have caused some disruption to research and extension activities. However, where possible, adaptations have been put in place so that the project team can continue to progress its work, with the following outcomes achieved:

• The first commercial sweetpotato crop was harvested from the long-term farming systems trial at the Department of Agriculture and Fisheries’ Bundaberg Research Facility. Soil samples for nematode, physical properties and soil biology analysis were taken just prior to the crop being dug, with data collected for yield and quality assessment. The results will be analysed to determine any correlation between soil characteristics, root knot nematode populations and soil biology.
• Activities to conduct smaller scale intensive sampling (especially on NSW farms) and on-farm cover crop trials were delayed, with Covid-19 border restrictions meaning that NSW agribusiness staff were contracted to collect soil surveys and facilitate possible cover crop trials in an effort to keep the research on track
• Pot trials continued, evaluating the nematode resistance or susceptibility of potentially suitable cover crops for use in sweetpotato faming systems. Signal grass, Sabi grass, Sunnhemp and Williams oats displayed good resistance to both to incognita and M. javanica. Pathogenicity pot trials also continue to evaluate commercially grown sweetpotato cultivars to gauge susceptibility or resistance ratings to nematode infection. Herbicide trials are underway to investigate efficacy in controlling sweetpotato volunteer plants.

Industry participants have been kept informed via various communication methods, including a Virtual Field Day in June 2020.

To date, the project team have achieved the following outcomes.

Masterclasses

Four sweetpotato nematode masterclasses were held in the major production areas of Bundaberg, Cudgen and Atherton in Queensland. Sweetpotato growers were presented with up-to-date information about sustainable soil health management and a variety of nematode control options. Participants were encouraged to discuss how various management practices could be integrated into their sweetpotato farming systems.

Field surveys

Intensive field surveys have been conducted at over 90 sites to understand the occurrence of region-specific nematode species and identify any potential biosecurity issues. Previous cropping history and a range of soil parameters, such as soil type, organic carbon, pH and carbon dioxide respiration, will be used to assess the impact of these factors on nematode occurrence and population density.

Project results were communicated to farmers and researchers through field days and project updates held in Bundaberg and Cudgen.

Long-term farming system trial

A long-term farming system trial has been established at the Bundaberg Research Facility in Queensland and will run for the life of this project. It will assess a range of tillage options, soil amendments, cover crops and mulches to improve biological soil health and provide long-term sustainable nematode management.

The trial will assess practices including rotation crops, reduced tillage, traffic control and organic amendments. Various combinations of these practices will be trialed with regular monitoring of nematode populations, other soil/biological characteristics as well as yield data.