Tomatoes (CA)

Crop production problems can occur if tomatoes don’t begin with a healthy root system. That's why it's vital to control the various kinds of nematodes that feed on the roots of tomatoes. If a field is heavily infested with nematodes, tomato seedlings could fail to fully develop.

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.

To help control nematodes, tomato growers are relying on the Telone® soil fumigants as the foundation for maximum yields and profits.

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

Fall Samples

Spring Samples

Percent of Normal Yield

0 to 160

0 to 25

100

620

100

95

940

150 

91

1,560

250

85 

2,190

350

79 

2,810

450

74 

3,440

550

69 

4,060

650

65 

5,000

800

60 

5,920

950

55 

 

 

 

 

 

 

 

 

 


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.


Symptoms of damage caused by nematodes can be found both above ground and below ground. These symptoms can become more pronounced following an increased rate of ethylene production, which is common in infestations of root-knot nematodes. Symptoms such as stunting and a decline in fruit quality normally occur in patches of nonuniform growth, as opposed to a complete decline throughout an entire field.

Plant-parasitic nematodes use a hollow tube – known as a stylet – for feeding by puncturing root cells and withdrawing nutrition from the tomato plant. The timing of the effects of nematode feeding is based on nematode population, crop susceptibility and environmental conditions.

If a field is heavily infested with nematodes, tomato seedlings could fail to fully develop and the plant will suffer poor stand development. With less severe infestation levels, symptoms may be delayed to later in the growing season and become more pronounced as the season progresses.

Typical above-ground symptoms

  • Stunting
  • General unthriftiness
  • Premature wilting
  • Slow recovery to improved soil conditions
  • Leaf chlorosis, or yellowing
  • Various other symptoms common with nutrient deficiency

Common below-ground symptoms

  • Nematode infection of roots results in swellings, or galls, and reduced root mass
    • Root galling results in reduced nutrient and water uptake, and premature drought stress leading to yield losses
  • Tight mat of short, swollen roots
  • Dead roots

In addition to monitoring visual symptoms, collecting soil samples is an effective method to determine the presence of nematodes.

There are numerous general management practices to take into consideration when determining how to manage nematodes. These practices include crop rotation with a nonhost or poor-host crop, resistant varieties, fallowing and chemical controls.
 
Not all of these methods will yield the same results, but they will each provide varying levels of nematode management. Most of these methods, with the exception of chemical controls, will gradually reduce the amount of nematodes in a field, whereas chemical control is more apt to quickly reduce nematodes. When possible, each method should be combined with other methods to produce the best results.

Four Practices Commonly Used to Effectively Combat Nematodes

 Crop Rotation  The most important aspect of an effective crop rotation is to find crops that are poor hosts for the nematodes commonly associated with tomatoes. Because numerous species of nematodes are commonly found in one field, it's important to select a crop that is a nonhost for root-knot nematodes, the most damaging nematode in tomato production.

Hairy indigo, American jointvetch, sorghum, rye, barley, wheat and pangola digitgrass have shown to be effective in limiting populations of root-knot nematodes.

Resistant Varieties  Resistant varieties are useful for control of some nematodes and diseases in tomatoes. Nematodes fail to develop and reproduce in the roots of resistant varieties, giving tomatoes a better chance to grow as they would normally. Growers should not rely on the same variety for disease control year after year and should change varieties to slow down the development of new problems. Additionally, not all nematode-resistant varieties of tomatoes have proven to be consistently resistant, so other practices like crop rotation and chemical controls should be used in concert with the resistant varieties.
 Fallowing  Having clean land is often a very effective method of reducing nematodes. Populations of nematodes hinge on the availability of a food source; without a crop to feed on, nematode levels will dwindle due to starvation. However, weeds and volunteer crops need to be controlled in a plowed, fallow field as nematodes have a wide host range. If properly managed, a fallow field can decrease the level of nematodes.
Chemical Controls  Nematicides, such as Telone® II soil fumigant, are proven to reduce nematode populations and, in turn, improve fruit production. Telone II is injected into the soil as a liquid and immediately converts to a gas, which creates a zone of protection around developing roots. As a fumigant, Telone IImoves through the soil on its own, rather than requiring water or incorporation of movement.