| CROP | NEMATODE | ||||
| ROOT KNOT | CYST | LESION | STEM & BULB | RESISTANT VARIETIES | |
| TOMATOES | YES | NO | N | NO | I,J,A |
| CUCURBITS | YES | NO | T | NO | NO |
| SUGARBEETS | YES | YES | T | NO | NO |
| ALFALFA | YES | NO | N,T | YES | YES |
| GRAIN | I,J,A | NO | T,N | OATS | NO |
| CORN | I,J,A | NO | T,N | NO | NO |
| SUNFLOWER | YES | NO | ? | NO | NO |
| SAFFLOWER | YES | NO | ? | NO | NO |
| BEANS | YES | NO | T | NO | YES |
| RICE | NO | NO | NO | NO | NO |
| FALLOW | NO | NO | NO | NO |
Examining the host range of the various species that might be present in a field in Yolo County, it quickly becomes evident that the more species of nematode present, the more difficult it becomes to develop a nonhost crop rotation.
Root-knot nematode is the most troublesome nematode in this cropping system, because all crops grown except rice are known hosts. The letters I, J, A indicate the species of root-knot nematode incognita, javanica and arenaria, respectively.
Corn does not typically exhibit damage in this cropping system, but serves as a maintenance host for root knot nematode which could then be damaging to a subsequent crop of tomatoes, cucurbits, sugarbeets, beans, safflower or sunflower.
Sugarbeet cyst nematode is also a problem and the sugarbeet acreage has dropped considerably in recent years due to a recent suspension of use of the nematicide 1,3-dichloropropene, and increase in a plant disease problem called Rhizomania (which is a virus vectored by a fungus).
There are references in the literature indicating that some rice varieties are hosts of root-knot nematode species found in California, but neither damage nor population build up have been demonstrated in California. If this were examined more closely, rice might become a useful crop for use in a nematode management program
The letters T and N indicate the species of lesion nematode Thornei and Neglectus, respectively. Altough P. thornei is known to cause serious problems on wheat in other parts of the world (e.g. Mexico), it is not considered a problem on wheat in Yolo County. This is probably due to the fact that wheat is grown in the winter below the activity threshold of the nematode. So growers may be utilizing a cultural management technique (date of planting) to avoid a nematode problem without even realizing it.
A grower with only cyst nematode present, has a wide selection of alternative crops and may plant sugarbeets every 4 to 8 years, depending on past history of the seriousness of the infestation.
What would be your advice to a Yolo County grower who called and asked for help in developing a crop rotation program?