What are These Hidden Pests Costing Growers?

Nematodes are nonsegmented, microscopic roundworms that live in various kinds of soils across the country. Some survive by feeding on plant roots, which results in poor crop health and reduced yield. Many different species of nematodes can be present in a tomato field, and they often share the same soil space within a field.

The two most common plant-parasitic nematodes in tomatoes are root-knot nematodes and sting nematodes. Not only do these nematodes inflict direct damage on the root system, but they also act as a vector for various fungal and bacterial diseases. Total yield losses differ depending on the species of nematode and kind of disease, with root-knot nematodes often causing the most damage.

Potential Crop Loss

The University of California, Davis, developed a table demonstrating the effect that certain root-knot-nematode populations can have on tomato yields. This table is based on sandy loam soils in the San Joaquin Valley and isn't necessarily accurate for soils outside of the area. Although the exact numbers may differ, the correlation between nematode population and yield loss is roughly the same. As the chart indicates, crop damage and yield loss increases as the population of nematodes increases.

Number of Root-knot Juveniles per Kilogram in Soil Samples

Source: http://www.ipm.ucdavis.edu/PMG/r783200111.html?printpage

Tomato producers can use this chart to help determine how much profit could potentially be lost due to nematodes. For example, if 450 juvenile root-knot nematodes per kilogram are found in a spring sample, yield would drop approximately 26 percent. If a normal yield is 20 tons per acre, the final yield would be 74 percent of 20, or 14.8 tons per acre. If tomatoes are $50 per ton, the value of the loss would be $50 multiplied by the 5.2 tons per acre lost, or $260 per acre.