merny… nematode found pathogen of imperial lettuce

I in the fall of 1967, the nematode Longidorus africanus Merny was found in soil around the roots of stunted lettuce seedlings in the Imperial Valley of southern California. The seedlings appeared wilted and chlorotic and the tips of the tap roots were swollen and sometimes necrotic. Greenhouse experiments proved L. africanus to be a pathogen of head lettuce, and field samplings during 1968 showed the nematode was widespread throughout the valley. Many crops such as cotton, sorghum, alfalfa and sugar beets are hosts of this nematode. Preplant soil fumigation with 1,3-dichloropropene hastened crop maturity and significantly reduced tap root damage. The reasons this pathogen was only recently discovered are believed to be primarily: (1) the previous absence of surveys for nematode pathogens of head lettuce; (2) shorter fallow period between lettuce and the previous crop; (3) recent precision planting of the lettuce.