7. 



Almost ail fields on sandy soil where daffodils are grovm are treated 

 regularly. 



Pratylenctius pratensis 



Although this nematode is far more widely spread than P. penetrans , 

 much less is knovm about its economic importance. Until now no con- 

 vincing cases of damage by this nematode have been reported, nor have 

 symptoms of the attack been described. The nematode attacks ail cereals 

 and quite a number of oth^r plant species. Many of them are also hosts 

 of P. penetrans . In some of these the latter nematode causes lesions 

 even wnen present in small numbers, whereas P« pratensis does not cause 

 any visible cnange of the attacked tissue (cherry, Piantago major , 

 peas). 



Most cases of damage, e.g. on cereals, white clover and grasses 

 reported in literature (e.g. OOSTENBRIWK 195U), are based on growth 

 improvement after treating the infested soil vrith a nematicide. Cereals 

 however do not show patchiness which shows close relations to the oc- 

 currence of high numbers of this nematode in the soil, i'he degree of 

 infestation of the soil varies widely even in the same field. So there 

 snould either be poor patches where the degree of infestation is high- 

 est or the (invisible) damage only occurs in a small part of some fields. 



The improvement of growth of white clover and grasses after DD 

 treatment from which Oostenbrink {19Sh) drew the conclusion that P. 

 pratensis caused damage to these plants, is most probably not due to 

 the killin,^ of parasitic nematodes. Ennik , Kort and van Doom (in 

 litt.) found that this growth stimulation also occurred where only 

 very low numbers of P. pratensis or other plant parasitic nematodes 

 were present. They could explain the effect of DD treatment on these 

 plants partly by an increase of the amount of nitrogen available to 

 the plant but concluded to the presence of one or* more other growth 

 stunulating actions of DD other tnan killing of eelworms (see also 

 Ooffart and Helling (1958). 



Pratylenchus thomei , P. minyus and P. neglectus are most prob- 

 ably comparable to P. pratensis in their relation to plant growth. 

 No trustworthy reports on damage are known. 



Effect of soil type on the occurrence of root lesion nematodes . 

 The distribution of all species of root lesion nem.atodes in the Nether- 

 lands and moot probably also in other parts of Western Europe shows a 

 close relation to soil type. P. penetrans seems to find optimum con- 

 ditions in organic soils or sandy soils rich in organic matter. It 

 also occurs on light sandy soils but was never found in the Wether- 

 lands on a true clay soil. P. pratensis is also widely distributed 

 on sandy soils but builds up~large populations on loamy sands and even 



