| ||Northern Root-Knot||Southern Root-Knot||Javanese Root-Knot||Peanut Root-Knot||Lesion||Ring||Dagger||Dagger|
| ||Meloidogyne hapla||Meloidogyne incognita||Meloidogyne javanica||Meloidogyne arenaria||Pratylenchus vulnus||Criconemella xenoplax||Xiphinema americanum||Xiphinema index|
|Marigold||Host||Host||Host, Trap Crop||Non Host|| ||Host|| || |
|Sudan, SS-222||Poor Host||Good Host||Host||Host||Non Host, Antagonistic||Antagonistic||Antagonistic||Nonhost|
|Barley, Columbia||Host||Poor Host||Good Host||Host||Non Host, Antagonistic||Host||Antagonistic||Nonhost|
|Cahaba White Vetch||Good Host||Poor Host||Host, Trap Crop||Host||Host||Host||Antagonistic||Nonhost|
|Salina Sweet Clover||Host||Poor Host||Poor Host||Nonhost||-||+|| || |
|Moapa Alfalfa||Susceptible||Poor Host||Poor Host||Nonhost||Non Host||Host||Host|| |
|Coker 916 Wheat|| || || || || ||-|| || |
|Nova II Vetch||+||-||-||-||-||-|| || |
|Blando Brome Grass||Host||Nonhost|| || ||Non Host||Host||Good Host||Poor Host|
At the present time, our knowledge is only sufficient to try to predict which cover crops will not exacerbate a nematode problem. We don't have sufficient knowledge of cover crops to predict which will produce reductions in nematode populations over and above what would occur in a fallow situation.
What can be seen from examining this chart is (1) that one must know which nematodes are present in a particular field before one can choose a crop that will be a poor host, or a non host, and (2) that the more types of nematodes present, the more difficult choosing a nonhost becomes. For example, Cahaba White Vetch is a poor host (but not a non host) for M. incognita, which is a common nematode problem in California orchards and vineyards. However, it is a host for P. vulnus and C. xenoplax which are also common in these situations.
A potentially useful management technique mentioned in the table is that of using cover crops as a trap crop. Trap cropping is a technique useful for removing a portion of the population of a sedentary endoparasitic nematode such as root-knot (Meloidogyne sp.) or cyst nematode (Heterodera sp.).
A host for the nematode(s) of interest is planted, allowed to grow for a time, and killed prior to the development of egg bearing adults.
It is important to destroy the roots of the crop so they do not continue to support nematode development. The technique is not useful for migratory ectoparasitic or endoparasitic nematodes because the juveniles and adults are able to move to other roots and continue to feed and develop.
One should also keep in mind that much of the research on cover crops has been conducted in microplot or small plot trials and caution should be used when expanding this research to larger situations. If one is going to plant a cover crop in an orchard for the first time, leaving some areas unplanted will allow comparisons to be made which will help to evaluate the effects of planting the cover crop.
McKenry has also conducted extensive research on the use of marigolds to reduce nematode populations. Although marigolds are a host to some species of nematodes, when they are either tilled into the soil and allowed to decompose, or soaked in water which is then applied to soil, nematode reductions have been achieved. Unfortunately, in some cases, phytotoxicity from the marigold extract has been severe enough to warrant caution in the use of this technique. Current research by McKenry with extracts of Cahaba White Vetch indicate that it may reduce nematode populations without as much risk of phytotoxicity.