Heter: 



The interpretation is briefly this. As the nematode population 

 gets higher it takes relatively more nematodes to create the same amount 

 of injury as it did initially. T think the reason for that is perfectly 

 straightforvjard in that, when there are a lot of nematodes in the root 

 they compete with each other and modify to some extent their om\ effect. 

 Thus, it requires relatively more nematodes to cause a big dimunition in 

 yield than it does to cause a small one. The first few nematodes pro- 

 duce relatively mcure effect. 



In the case of sugar beets one is not only interested in yield but 

 also in sugar percentage. In some of the old literature you will find 

 that the sugar beet eelworm is said to decrease the sugar percentage. 

 Plotting the effect of the initial nematode population against the per- 

 centage sugar (Figure 2) does show an apparent increase in the sugar. 



SUGAR 



IiMlTlAL I^IEMAtODE POPULAtIuN 



Figui-e 2. Sugar content of beets in relation to initial population. 



The explanation is that this is the normal thing in that, the 

 smallest roots have the highest sugar percentage. Sugar beets exposed 

 to increasing levels of nematode population produce smaller roots, where- 

 as the more noimal large roots which develop from being exposed to lower 

 inocultmi levels have a lower sugar count. It appears that the eelworm 

 has a very limited effect, if any at all, on the sugar physiology of 

 the sugar beet root. This would sup;'?;est that the toxins which are pro- 

 duced by the nematodes remain localized and haven't spread far into the 

 main tap root. That, of course is only a hypothesis, and I wouldn't want 

 to press this too far, because many other things go on in the sugar beet 

 root besides sugar production. 



POPULATION STUDIES; Generations 



Next, I would like to deal ^^th the number of generations of the 

 nematode which may develop in a year. In order to get the maxijnum num- 

 ber of generations, the soil must be in the right sort of physical con- 

 dition and above all have sufficient moisture. During the summer months 

 in the eastern part of England and probably, for all I know, in the 

 United States and elsewhere, one finds that there is in vrell-drained 

 soils a period during July and early August that soil moisture is limited, 

 VJhen the amount of moisture in the soil is not adequate to pennit s\if- 



