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Nematode threshold levels

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Threshold levels (nematode population levels which justify the implementation of control measures) are dependent on the variables described above. At this time there is very little experimental data to establish threshold levels for golf greens in Massachusetts and New England. The numbers listed in Table 23 are based on research from other states as well as from case history information and survey results compiled in our region. These numbers are meant to serve as a guide only and are subject to change.

Table 23. Guide to approximate threshold levels for nematodes in turf for the Northeast.

Nematode No. / 100cc soil *
needle 100
lance 400
stunt 800
spiral 1,500
ring 1,500
lesion 100
cyst juveniles 500
root-knot juveniles 500
stubby root 100
sting 20

* Note: These threshold levels were developed when a nematicide capable of stopping nematode populations from developing further was commercially available. The thresholds listed here are not meant to imply that damage would occur at these levels. Some stress may occur at these levels, but at 2x or 3x these numbers damage would likely be evident.

Assessing damage caused by nematodes

High populations of certain species of nematodes may indicate that the root system has become debilitated to a significant extent. However, this information should be evaluated in context with past and prevailing circumstances. For example, all of the following factors are important in the development of a diagnosis and recommendation: species and numbers of nematodes present; depth at which the sample was taken; turfgrass species composition; depth of root system; soil texture; symptoms and extent of damage; potential contamination of the environment by a nematicide; and presence of other stresses to turf.