Control B!2 



penetration of the heat is required. Other, as yet, little investigated 

 possibilities include the use of ultrasonics, high frequency heating, 

 and irradiation treatments. Destruction of nematodes in the environ- 

 ment, whether this be the soil, the greenhouse bench, the flat or flower 

 oot, is done by various techniques usually based on one of the follow- 

 ing principles: a. Heat - hot water drenches or soaks, steam, flame, 

 electrical resistance, heated inclosures such as ovens and pressure 

 containers^ b. Exposiire - exposure to the effects of sunlight and desic- 

 cation; c. Electricity - probably effective only by production of heat, 

 rather than by the electrical effects alone; and d. Chemical - as is 

 covered in the section dealing with chemical control of nematodes. 



Attrition is a form of eradication which has taken many forms in actual 

 practice, but which has as its goal "making life too tough" for the 

 nematodes to thrive. The principles involved include inactivation, 

 starvation, and antibiosis. Removal of carry-over and weed hosts, 

 falloirring, flooding, tillage, and crop rotations are possibilities used 

 vjhen feasible. Antibiosis has been used in some instances as a nema- 

 tode control in commercial plant production and is a fertile field for 

 further research. Antibiosis involves the application and manipulation 

 of the biological factors of the environment in such ways as to be 

 detrimental to the plant-parasitic nematodes present. . Examples are the 

 use of trap crop plants such as Crotolaria, and green manure to promote 

 development of nematode- trapping fungi. Other possibilities include 

 the use of antibiotics, predacious mites and nematodes, and introduction 

 of the various bacterial, fungal, and protozoan pathogens causing dis- 

 eases of nematodes. Isolation, identification, and synthesis of nema- 

 tode effecting root exudates is now being done and may be effective for 

 some kinds of nematodes. 



III. Protection . Protection is a low-cost form of nematode control 



which is applied in situations where parasitic nema- 

 todes are thought to be present. In its simplest forms it may be 

 nothing more than manipulation of the environment in such a way that 

 nematodes are not blown, washed, splashed, or transported from infested 

 to non-infested sites. Control of nematode dissemination may also be 

 had by choice of planting sites, plant spacing, and planting dates. 

 The use of protectant materials has not been very much explored, and 

 although this is in the realm of chemical control, the concept bears 

 mentioning here. One should keep in mind that for many of the annual 

 plants, a satisfactory economical control is attained if the plants 

 can be protected from the nematodes long enough to get a vigorous root 

 system well started. After that, the plant may be able to support the 

 nematodes which attack it and yet prove to be a worthwhile plant. 



rv. Resistance . This is probably the ultimate goal in the development 



of control for all plant diseases. There are nematode 

 resistant varieties of some crop plants, and others are being developed. 

 The problems in producing nematode resistant plants are difficult be- 

 cause of the numerous kinds of plant-parasitic nematodes, the fact that 

 usually more than one species is present, and the interrelationship of 

 nematodes with other pathogenic organisms in disease complexes. 



