As our nematode survey continues, more questions are being asked about nematodes, their damage potential, etc. Following is an update on the survey:
- Do not attribute all vague symptoms to nematodes. Nematode populations and symptoms are extremely complex and cannot be diagnosed by anyone other than a nematologist. In other words, don’t panic.
All samples submitted so far have tested positive for some sort of turf parasitic nematodes, mostly Ring nematodes.
Samples have tested as high as 2600 ring nematodes/100 ml of soil.
In most case,s no visible symptoms are present, even on the over 2000 nematode/100 ml green, as few other stressing factors are present at this time.
However, one green in Indianapolis may be showing symptoms of nematode damage, but this is very difficult to distinguish and isolate as the primary problem.
Damage symptoms would include yellowing patches, thinning, enhanced drought stress, little or no response from fertilizer, and other symptoms reflective of a poor root system.
Though thresholds are routinely published for determining control measures, these thresholds are complicated because symptom expression may be enhanced or complicated by poor rooting from summer weather, compaction, take-all patch, summer patch, natural decline of Poa annua, and other factors. That being said, following is a table of damaging thresholds from Nematode Parasites of Turfgrass, publication RPD No. 1108, from the Univ. of Illinois.
| Damage thresholds for frequently encountered nematodes of turfgrasses in Illinois | |
|---|---|
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| Nematodes | Nematodes/100c soila b |
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| Lance | 76+ |
| Lesion | 51+ |
| Stunt | 100+ |
| Dagger | 51+ |
| Spirals | 300+ |
| Ring | 300+ |
| Pin | 501+ |
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| a Combinations of nematodes, especially lance, lesion, and stunt, may cause problems at lower population densities. | |
| b Eliminate pH, fertility, soil compaction, soil insects, diseases, etc., as possible factors limiting growth before using a nematicide. | |
- We will try follow-up sampling on some of these greens during this summer.
If symptoms are suspected, we do not recommend broadcast treatment. We’d first try a strip treatment or two of Nemacure. Effects on nematode numbers should be seen within 3-5 days. If successful, symptoms should start to decline within a week depending on growing conditions. The difficulty of applying Nemacure dictates that it should only be used in extreme cases.
There’s an excellent source for nematode information entitled “Nematode Parasites of Turfgrass, publication RPD No. 1108” from the Univ. of Illinois at at http://web.aces.uiuc.edu/vista/pdf_pubs/1108.pdf