Sample for nematodes
Diagnosing nematodes can be a frustrating exercise. Because nematode symptoms often resemble other kinds of stress, laboratory analysis is a vital tool for assessing nematode problems. However, an analysis can only be as good as your samples, so correct sampling procedures are critical.
Use the proper tools Nematode sampling basically is just soil sampling--after all, that is where nematodes live. Conceivably, then, you could use any digging tool. However, each sample should be similar in depth and volume. Therefore, it's best to use a typical soil probe or "tube" that allows you to obtain consistent sample size and depth. Additionally, soil probes disturb turf relatively little compared to other methods and are simple and quick to use. Cup cutters are suitable, though they may require you to handle larger amounts of soil than are really necessary. In ornamentals, you can use a trowel or other digging tool, though a soil probe still is the most efficient method.
Ensure even sample distribution in turf Knowing that nematode populations vary--over time as well as from place to place--is the key to obtaining accurate samples. Although you could take a single sample from an affected area (if nematodes are causing the problem, you should see high counts there), it is best to take multiple samples throughout the affected area to get a more representative overall picture.
* Horizontal distribution. Nematode counts can vary widely even between samples taken just a foot or so apart. Therefore, a single sample can be misleading. A composite sample of 15 to 20 cores from throughout an affected area usually provides a fairly reliable estimate of the nematode population. Concentrate on turf that's showing symptoms but is still alive, and avoid dead or bare spots.
* Vertical distribution. Nematode distribution also varies by depth. For this reason, it is important that you take soil samples at a consistent depth--4 inches (for greens) to 6 inches usually is adequate for turf. Deeper soil contains fewer roots and, therefore, fewer nematodes.
* Comparison samples. Take a composite sample from an apparently healthy area nearby to compare with the problem area. This provides a means of confirming that nematodes actually are the cause of the symptoms you are seeing and may give you some basis for knowing what levels your turf can tolerate.
* Seasonal variation. Nematode levels normally rise and fall over time, and the populations of different species peak at different times. However, when symptoms are occurring, it's obvious that nematodes (if they truly are the problem) are active and abundant. Therefore, if a problem exists, sampling when symptoms are apparent will provide good samples for analysis.
Some authorities recommend taking composite samples from a putting green 4 or 5 times during a growing season. This is a lot of effort but can be revealing. Thus, the expense may be justified for high-value turf, such as a golf green, that is suffering from nematodes. You'll only need to do this once to get a good picture of the seasonal population dynamics. It will tell you which nematodes are affecting your turf and give you a much clearer idea of how their numbers fluctuate throughout the year.
Sampling ornamentals is slightly different As with turf, you can obtain a representative sample by taking several cores from around ornamentals: beneath the dripline of shrubs and trees or within the root zones of annuals or other herbaceous plants. Be sure the soil samples include fine roots--if roots aren't present, parasitic nematodes won't be either. In ornamental plantings, you usually don't have to worry about the surface disruption that sampling can cause, so trowels or other digging tools will substitute adequately for soil tubes. In either case, take the samples from a similar depth--6 inches or so--but discard the top inch of soil, which will contain few, if any, nematodes.
Some plants' roots display conspicuous root deformation in response to nematode attacks. If you are finding roots with visible swellings or deformations, be sure to include some with your submission to the lab. (You may even be able to make a preliminary diagnosis yourself based on root symptoms.) If you suspect infestation of just one or a few plants, take several samples of "feeder" roots from these plants, along with some of the surrounding soil.
Handle samples carefully The laboratory to which you are sending your samples probably will provide instructions for collecting and shipping the samples, and you should always follow their directions. If the laboratory does not supply thorough guidelines, those listed here ensure delivery of a fresh, useful sample to the laboratory.
Usually, labs ask for about 1 to 2 pints of soil. If you have more soil in a composite sample than you need, mix it thoroughly in a bucket, and then draw your final sample from it. Some labs ask that you discard turf's top growth before submitting the sample. This makes the sample easier to handle and process.
Submit each sample in a tough, zippered bag, and then seal it with tape. Do not put paper labels inside the bags, because moisture causes the paper to disintegrate. Instead, use a black marker to label the outside of the bag. Be sure to provide the lab with as much information about the sampled site as possible, including soil and other environmental conditions, cultural practices, site history and turfgrass species. The lab may provide you with forms on which to write this information. Remember to keep maps of affected areas, including notes on where you took samples. This ensures that you can correctly match lab results with the areas from which you took the samples.
High temperatures and drying can kill nematodes, producing misleading laboratory results. Thus, it is important to prevent the samples from overheating and desiccation--keep them between room temperature and refrigerator temperature. An insulated cooler is a good receptacle for samples until you can deliver them to a lab. Avoid placing samples in the sun, on hot ground or anywhere else where temperatures may be excessive. Get samples to the lab as quickly as possible, within 1 or 2 days at most. Use overnight shipping if you can't deliver the sample personally, and package the samples so that they do not overheat during shipping.
* Use a tool such as a soil probe or "tube" for sampling. * Take samples from a consistent depth -- about 4 to 6 inches. * Take 15 to 20 samples from the affected area and combine for a composite sample. * Sample turf that's showing symptoms, but avoid bare or dead areas. * Label samples carefully, and keep accurate notes and maps. * Package and ship the samples so that they arrive at the laboratory quickly and in fresh condition. Protect against overheating.
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