By Wayne O’Neill and Rosalie Daniel

Key points

Guava root-knot nematode was first reported in the Northern Territory in 2022.

• New research, funded by Hort Innovation using the vegetable grower R&D levy, is set to develop better diagnostic capacity and identify options for management of GRKN.
• Growers, agronomists, and researchers learnt from the US experience in managing GRKN.
• Five pillars to managing root-knot nematodes: crop rotation, cultivar choice and establishment, soil management, targeted control, monitoring and evaluation.

A juvenile guava root knot nematode. Photo ©Wayne O’Neill.

It stunts plant growth by damaging their roots and disrupting uptake of water and nutrients. Tuber crops may also be damaged or blemished, impacting on their saleability. GRKN likes warm weather and is well suited to the northern regions of Australia. One of the bigger challenges in managing GRKN is that it can infect and damage crop cultivars that are resistant to the other major species of root-knot nematode.

To date, GRKN has been found in the Northern Territory and Queensland, but its full distribution and potential range remains uncertain. Tools to support rapid identification, and to distinguish this from other root-knot nematodes, need further development and uptake.

Building Australia’s capacity for GRKN management and preparedness

Led by the Queensland Department of Agriculture and Fisheries (QDAF), Hort Innovation is funding a project aimed at improving the management of GRKN in the Australian vegetable industry.

The project will survey and sample to better understand the current distribution of root-knot nematode species, including GRKN, in vegetable production regions around Australia. This will help to inform management options for different geographic and climatic regions. Improved diagnostic assays will provide confidence in accurate and more rapid identification of rootknot nematode species from root and soil samples to support farm management decisions.

The project will also evaluate a range of management options under greenhouse conditions, including assessing the resistance to GRKN of a range of cover crop plants and available nematostatic options suitable for commercial use. The project will run until July 2026.

US expert shares GRKN management insights

Dr Johan Desaeger, Associate Professor of Entomology and Nematology at the University of Florida, recently visited Australia to share valuable experiences in management of GRKN based on his research in Florida and other regions impacted by the nematode. Farmers in the US have been managing GRKN for more than 20 years.

Dr Desaeger presented at the Bundaberg Fruit and Vegetable Growers Multipest info session in August 2024, providing local growers, agronomists and researchers with a unique opportunity to better understand this emerging pest and its potential impacts on local horticulture.

At the Australasian Soilborne Diseases Symposium in Kingscliff, NSW, Dr Desaeger delivered a talk on integrated nematode management (INM) and FindMe – a US program to support growers to manage the pest in their vegetable crops through understanding the distribution of the nematode and the options for breeding, chemical, biological and cultural control of the pathogen. He also participated in a nematology workshop for Australian researchers, held as part of the symposium.

Dr Desaeger’s visit facilitated direct engagement between Australian growers, agronomists, researchers and allowed for in-depth discussions and knowledge sharing with real-life experience of the nematode in the US. This knowledge exchange is crucial for developing effective strategies to mitigate the potential impact of GRKN on Australian horticulture, underscoring the importance of international collaboration in addressing agricultural challenges.

Learnings from the US

Guava root knot nematode infection can result in losses in yield and quality. The FindMe project surveyed the distribution and management of GRKN in the vegetable growing regions of the southeastern US (Florida, Georgia, South Carolina and North Carolina) and found that the nematode was most common in central and south Florida (in Asian vegetables, pepper, tomato), and in North Carolina (sweetpotato).

FindMe researchers continue to work on developing GRKN resistant germplasm in sweetpotato, cucurbit crops and capsicum. The project is also assessing a range of chemical and biological nematicides, cover crops and rotations. Learnings from this project are part of the knowledge exchange benefits from Dr Desaeger’s visit to Australia.

Good biosecurity practices

To reduce the risk of GRKN from entering your farm or property, growers are encouraged to implement good farm biosecurity practices which include:

• Visibly inspecting plant material arriving on your property to ensure it is healthy and is free of pest and pathogen symptoms.
• Sourcing clean planting material and growing medium from reputable suppliers.
• Keeping records of where plants/planting material are sourced from, and where and when they are planted on your property.
• Ensure all visitors and staff disinfect equipment, vehicles, and footwear to reduce spread from infected properties.

If you suspect your property may be affected, phone the Exotic Plant Pest Hotline on 1800 084 881. This will put you in touch with your state or territory’s biosecurity agency.

Five pillars for integrated nematode management

At the ASDS meeting, Dr Desaeger presented five pillars for integrated nematode management (INM), noting that there is no ‘one-size-fits-all’. Different options will suit for different situations and different farms.

1. Crop rotation was described as the foundation of any nematode management program. Crop rotation with a cash crop is not always an option, but cover crops are a form of crop rotation. For plant parasites with a wide host range (like root-knot nematodes), it is critical to rotate with non-host species to reduce pest numbers between susceptible crops. Benefits also include improvements in physical, biological and chemical soil properties and water holding capacity. Adding diversity to rotation crops can further increase these benefits, but to maintain nematode control care has to be taken to ensure all rotations are resistant. Studies in maize have shown that increasing rotational diversity in maize-based North American
cropping systems improved maize yields over time and across all growing conditions, including during droughts (Bowles T.M. et al. One Earth, 2, 284 – 293).

2. Cultivar choice and establishment – selecting cultivars that are tolerant or resistant to the target nematode, where available, is an important element of an effective nematode management program. Planting/harvesting dates can also be varied to assist with crop establishment and to help avoid conditions that favour rapid nematode build-up.

3. Soil management or soil health management harvests the soil’s capacity to suppress the nematode, for example by building up beneficial organisms such as nematode trapping fungi. Strong and healthy plants are also more resilient to pests, diseases and stress.

4. Targeted control – most farmers in Florida still fumigate before planting, but this kills a huge range of beneficial organisms, including the natural enemies of the pests being controlled. Targeted chemical application is becoming more common as newer, more selective and safer nematicides are becoming available (e.g. Nimitz – fluensulfone). Dr Desaeger was impressed by the targeted chemical usage he observed on farms he visited in the Bundaberg region.

5. Monitoring and evaluation should be included in a management system as good practice. Knowing which nematode species are present helps with management as host ranges differ. Different nematode pests (even different root-knot species) may damage different crops and also require varying rotation crops for management. Pre-plant nematode counts can help make management decisions, e.g. for chemical application. Every time soil, roots or tubers are moved, there is the potential to move nematodes (and other soilborne pathogens), so on-farm monitoring and biosecurity is critical!