SUMMARY OF HOST-NEMATODE RESPONSES ON COVER CROPS:

  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

DATA SUMMARY BY M.V. MCKENRY, 1991

+ = PROBABLE HOST, - = PROBABLE NONHOST, BASED ON DATA FROM GEORGIA AND S. CAROLINA

M. V. McKenry at the U.C. Kearney Agricultural Center south of Fresno has conducted the most extensive research on the susceptibility of cover crops that might be useful in perennial cropping situations in California. This chart summarizes much of that work plus research conducted by the USDA-ARS in Georgia and South Carolina. Additional information on cover crops can be gleaned from the various nematode-host association databases available over the WWW.

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.

KNOWLEDGE EXPECTATIONS