Nematode Threshold & Treat, Monitor or Safe

By the ratio of the soil count to the crop's damage threshold. Ratio = nematodes per 100 cc ÷ damage threshold. At a ratio of 1 or more the count has reached or passed the threshold, so the tool says treat. From 0.5 up to 1 it says monitor — the population is building toward damage. Below 0.5 it reports safe, well under the level where yield loss begins.

It is a count of plant-parasitic nematodes extracted from a standard 100 cubic centimetre (about 100 gram) portion of soil. Labs report counts on this basis so results can be compared against published damage thresholds. Enter the lab figure for your sample, or your own extraction count standardised to 100 cc.

It is the nematode population at which a crop starts to lose measurable yield — the point where treating pays off. Thresholds vary by nematode species, crop and soil type; root-knot on a sensitive vegetable has a much lower threshold than a tolerant cereal. Use the published threshold for your specific nematode-crop pairing.

A ratio of exactly 1 means the count equals the damage threshold — the population has reached the level where economic yield loss is expected. At or above that line the cost of control is justified by the yield it protects, so the tool recommends treatment. Below it, the loss does not yet warrant the spend.

Nematode populations build over a season. A ratio between half the threshold and the threshold means damage is approaching but not yet certain — the right move is to monitor, resample later, and be ready to act if the count climbs. Treating this early can waste money on a population that may not reach the damaging level.

Take many small cores across the field, mix them into one composite sample, and keep it cool and out of the sun before sending to a lab. Sample at the right depth in the root zone and at a consistent time of year so counts can be compared to thresholds and across seasons. Poor sampling is the biggest source of misleading nematode results.

Yes. The same nematode count can be safe for a tolerant crop and damaging for a sensitive one, so the threshold you enter must match the crop you are about to grow, not the one just harvested. Always pull the threshold from guidance for the planned crop and the nematode species present.

Options include rotating to a non-host or resistant crop, using nematode-resistant varieties, soil amendments and biofumigation, fallow or solarisation, and registered nematicides where allowed. Cultural and rotational tactics are often cheaper and more durable than chemicals; the ratio simply tells you that doing nothing risks yield.

They're solid working figures for a decision. Nematode counts are variable and thresholds are guidance, not hard cut-offs, so treat the ratio as a strong signal rather than a guarantee. Confirm with lab results, local advice and field history before committing to a costly treatment.