Collecting samples for nematode analysis for citrus and grapevines	AG0198
Megan Edwards, Muldura September, 1994

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Nematodes feed on plant roots and so are found within the plant root-zone. Samples collected for nematode analysis must be obtained from within this zone. Nematode populations vary according to the depth of soil. Collect soil samples between the depths of 100 mm and 300 mm only. Sampling beyond 300 mm depth is unnecessary, as the nematode population declines with increasing depth. Surface soil is subject to tillage, temperature extremes and moisture variation and hence should be avoided when sampling.

The ideal time to collect soil samples for the assessment of numbers of root-knot nematodes is during September and October. The young root-knot nematode larvae hatch from eggs in early spring and are present in their highest numbers at this time. The population of the citrus nematode does not undergo significant seasonal fluctuations. Therefore soil samples taken to determine levels of citrus nematode can be collected throughout the year.

Sampling method

Each soil sample should contain about one kilogram of soil, collected from at least six sub-sample sites. Soil taken from each site is known as sub-sample soil and all sub-samples are bulked together to form the final sample. This sample is then submitted for analysis. Sub-sample sites should be selected at random over the total area requiring assessment. Note that the number of sub-sample sites must be at least six. In fact the greater the number of sub-samples collected, the greater will be the accuracy of the nematode count in the given area.

Only one sample is required for:

a single plant an area of uniform plants

Changes in soil type, plant variety and/or rootstock may justify the collection of separate samples. However, whenever possible, the number of samples submitted for analysis should be limited to a single sample. Accuracy over a large area (several hectares of plantings) can be achieved by collecting more sub-samples. In most cases samples submitted from adjacent areas, or from healthy and weak areas within the same planting, tend not to show differences in nematode levels.

Differences in numbers of soil nematodes between healthy and poor areas are not evident because the still healthy plant is able to support as many, or more nematodes as the less vigorous plant that has fewer active roots. When sampling such areas, take only one sample. Select the majority of the sub-samples from the edge of the poor patch. Make up the sub-sample numbers with soil collected from within the area of poor growth and from sound plants adjacent to this area.

Sampling procedure

How it is done?

Soil sampling
When collecting a soil sample only a shovel and a container for the soil are required. The soil sample is obtained by shovelling the surface soil aside. A hole is then dug and cleared to the appropriate depth (up to 300 mm). A soil scraping 10-20 mm thick can then be taken from the vertical side of the hole. Remember that only one kilogram of soil is required in total, so that less than a handful of soil is required from any one sub-sample site. Put the soil in a waterproof container (plastic bags are ideal), and ensure that the sample is clearly labelled with waterproof writing, preferably on the container or on a label tied to the outside. Do not put paper labels inside the container.

Plant root sampling
When collecting a root sample try to keep soil around the roots to stop them drying out. Make up a sample from at least six sub-sample sites. Plant roots should be included in soil samples taken from vine or citrus plantings.

Vines

Soil samples from vines should be collected from within 600 mm of the vine butt. Some secondary and fibrous vine roots should also be included in the sample. Careful examination of young vine roots can reveal root damage caused by the root-knot nematode or the root lesion nematode. A soil analysis is used to determine the presence of the citrus nematode in vines and to confirm the presence of other nematodes.

Citrus

Soil samples for citrus should be collected from just inside the skirt of the tree. Some secondary and fibrous citrus roots should also be included in the sample. An examination of citrus roots can indicate the presence of the citrus nematode. This is confirmed by carrying out a soil analysis.

Storage

All samples should be kept in sealed plastic bags to prevent drying out. They should be refrigerated at around 4°C. Make sure that they do not freeze.

Advice sheet

An advice sheet, which requires details of plant variety, known rootstocks, planting age, total area, plant vigour etc., must be completed and forwarded with the soil sample requiring analysis. These sheets are available at district offices of DPI. The grower and/or the district adviser should make sure that the details are provided to enable accurate assessment of the nematode problem.

Results

Nematode populations in soil samples are classified as low, medium or high. For example:

	Numbers of nematodes per 500 grams of soil
	Low	High
Citrus nematode Root rot nematode	Less than 1 000 Less than 100	More than 3 000 More than 300

Conclusion

Having assessed the nematode populations, associated crop and management factors are then considered. The information is used to determine the significance of the nematodes in the planting, and what action can be taken.



The advice provided in this publication is intended as a source of information only. Always read the label before using any of the products mentioned. The State of Victoria and its employees do not guarantee that the publication is without flaw of any kind or is wholly appropriate for your particular purposes and therefore disclaims all liability for any error, loss or other consequence which may arise from you relying on any information in this publication.