Nematodes in vineyards

Why nematodes matter

While many soil nematodes are beneficial and contribute to soil biodiversity, some species can reduce vine health, vigour and yield if left unmanaged. Nematode problems often go unnoticed until vines begin to lose vigour or yield.

Plant-parasitic nematodes are estimated to cost the Australian grape and wine sector around $14 million annually. Production losses of 5–15% have been reported in many grapegrowing regions, while severe root-knot nematode infestations can result in substantially greater losses. Nematodes damage root systems, reducing a vine's ability to take up water and nutrients. This can lead to:

• reduced vine vigour
• stunted growth
• uneven vine growth
• lower yields
• greater susceptibility to drought and other stresses
• increased vulnerability to root diseases.

Dagger nematodes can transmit grapevine fanleaf virus and may contribute to additional vine health and productivity losses.

The most effective time to assess nematode risk is before planting or replanting, when rootstock and site management decisions can still be adjusted.

For growers, nematode pressure can influence important management decisions including:

• rootstock selection
• site suitability assessments
• vineyard redevelopment planning
• cover crop selection
• soil management programs
• targeted use of nematicides.

Key points

• Nematodes can reduce vine vigour and yield.
• Root-knot nematodes are the most significant species in Australian vineyards.
• Symptoms can resemble nutrient deficiency or water stress.
• Laboratory testing is required for diagnosis.
• Rootstocks remain the most effective long-term management option

Common plant-parasitic nematodes in Australian vineyards

The species considered most significant in Australian vineyards include:

Root-knot nematodes are generally regarded as the most important nematode pest in Australian vineyards. They cause characteristic swellings (galls) on roots that restrict water and nutrient uptake, reducing vine growth and yield.

Different nematode species favour different soil types. Root-knot nematodes are more commonly found in sandy and sandy loam soils, while citrus and root-lesion nematodes occur across a wider range of loam and clay soils.

Signs of nematode infestation

Above-ground symptoms are often non-specific and can be mistaken for nutrient deficiencies, water stress or other root problems. Nematode infestations frequently occur in patches, creating areas of weak or unproductive vines within a vineyard.

Look for:

• poor vine growth compared with surrounding vines
• reduced shoot growth
• declining vigour
• patchy areas of weak vines
• lower yields
• reduced response to irrigation or fertiliser applications.

Root symptoms vary between species and may include:

• root galls
• root lesions
• thickened roots
• root discolouration
• bnormal fibrous root growth.

Because symptoms alone are not reliable, laboratory testing is required to confirm an infestation.

Monitoring and diagnosis

The most effective way to identify nematode problems is through soil and root testing.

Consider testing:

• before planting or replanting vineyard blocks
• when unexplained declines in vine growth occur
• when selecting rootstocks for redevelopment projects
• before purchasing planting material for sites with a history of horticultural production.

Laboratory testing can identify the nematode species present and estimate population levels. This information helps determine the likely risk to vine growth and yield.

Management options

Effective nematode management usually requires a combination of approaches rather than relying on a single control method.

Select resistant rootstocks

Rootstock selection remains one of the most reliable long-term management strategies, particularly where root-knot nematodes are present.

Before planting a new vineyard or reworking an existing block:

• test soils for nematodes
• match rootstock resistance to the nematode species present
• incorporate nematode risk into redevelopment planning.

Rootstock selection should consider both nematode resistance and how the rootstock influences vine growth, vigour and management requirements.

Early investment in resistant rootstocks can reduce future productivity losses and replanting costs.

Improve soil health

Soils with good structure and higher organic matter levels generally support more diverse soil biology.

A biologically active soil may help suppress some plant-parasitic nematodes while also improving root growth and resilience.

Practical actions include:

• maintaining groundcover
• increasing organic matter inputs
• minimising soil degradation
• supporting soil biodiversity through integrated soil management practices.

Use cover crops strategically

Research has identified opportunities to use certain cover crop species to help suppress nematode populations.

Brassica species such as mustard, radish and canola contain naturally occurring compounds called glucosinolates. When these plants break down, they release biologically active compounds that can suppress nematodes through a process known as biofumigation.

Research has shown that Nemfix Indian mustard grown in vineyard mid-rows and incorporated beneath vines can significantly reduce root-knot nematode populations.

Some cover crop species are non-hosts for root-knot nematodes, including:

• oats
• ryegrass
• fescue
• cocksfoot.

These species may help reduce opportunities for nematode population build-up. However, they do not provide the biofumigation benefits associated with brassica cover crops.

Cover crop-based suppression is generally most effective when treatments target the vine row, where most vine roots and nematode activity are concentrated.

Apply nematicides where appropriate

Registered nematicide options for viticulture are limited.

Where chemical control is appropriate:

• target treatments to known infestation zones
• focus applications along vine rows where most vine roots occur
• use laboratory testing and monitoring results to guide decisions.

Targeted applications are generally more effective than treating entire vineyard blocks.

Consider biological control options

Some fungi, bacteria and other beneficial soil organisms can help suppress nematode populations.

These approaches are most effective when incorporated into a broader integrated management strategy that includes soil health, monitoring and resistant rootstocks.