PART II. 



Nature of the Problem in Controlling Nematodes. 



The problem of nematode control is not the same in all latitudes 

 or in all countries but is determined by the nature of the conditions 

 which practical growers have to deal with. In the Southern States 

 and in those countries in which the winters are mild nematodes can 

 exist in the soil during the whole winter without any detriment, 

 whereas in the latitude of New England where the winters are cold 

 and prolonged the parasitic form Heterodera cannot survive. As a 

 result of this the parasitic species, the Heterodera, finds its proper 

 habitat in the greenhouses where the soil is kept from freezing and 

 it also survives the winter to a large extent in unfrozen manure 

 heaps. This statement does not hold, however, with the non-para- 

 sitic species of nematode, inasmuch as these forms or at least their 

 eggs are capable of standing an exceedingly low temperature and we 

 have never failed to find them in all kinds of garden soil, or, in fact, 

 in any soil which contains abundant decomposing organic matter. 

 These non-parasitic forms are frequently found in decaying vege- 

 tables of all sorts and we have many times observed them in the 

 laboratory on decaying matter which had evidently been subjected 

 to no source of contamination except ordinary water from the faucet. 

 The fact that Heterodera cannot stand our New England climate 

 greatly simplifies the problem of controlling nematodes, for here we 

 have the problem confined to our greenhouses and manure heaps 

 and not to hundreds of acres of soil as is the case in the milder cli- 

 mate of Europe and that of the Southern States. Heterodera, how- 

 ever, does occur occasionally in some of our outdoor plants but such 

 cases are always where the plants with their contaminating" soil have 

 been removed from the greenhouses as in the case of violets, etc., or 

 else where nematode infested manure has been applied to the soil. 

 It must be evident, therefore, that any rational treatment pertain- 

 ing to nematodes must take these facts into consideration and 

 must especially bear in mind the sources of contamination. Then 

 again we must pay some attention to the life history of nematodes in 

 order to be successful in controlling them. We have already shown 



