3. 



The cyst forming nematodes, Heterodera species 



Aithougti many agrlciiltural and a few horticultural crops may 

 be attacked by one of the seven Heterodera species occuring in Europe, 

 the importance of tins group is largely due to the tranendous damage 

 done by two species to two important agricultural crops, H. rosto- 

 cniensis on potatoes and H. schachtii on sugar beets. Damage by 

 these species is always associated with grox-ang their main host crops, 

 potatoes and beets respectively, in short rotations. 



The beet cyst nematode became an important parasite in the sec- 

 ond half of the 19th century in areas around sugar factories in Ger- 

 many and the Netherlands, where often sugar beets were grown on the 

 same field for several years in succession. 



The potato cyst nematode cropped up in the beginning of this 

 century in the potato growing districts of Lancashire, England, in 

 Scotland and around Rostock in Northern Germany. It has been found 

 since in all European coiinti*ies always in association witn intensive 

 cropping with potatoes, e.g. m allotment gardens, early potato grow- 

 ing areas, areas particularly suited to growing potatoes (Fen lands 

 in England and "Veenkolonien" in the Netherlands) and land in use by 

 refugees in post-war Western Germany, 



H« rostochiensls has been found to occur over a large area in 

 Peru,'~hence it has been generally accepted that it was brought into 

 Europe from these regions in recent times. It has been spread since 

 with infested seed potatoes and soil clinging to potatoes and other 

 plants. 



When the disease was recognized in England and Germany in the be- 

 ginning of this century, wide areas were already heavily infested 

 in these coitntries. Other countries such as the Netherlands apparently 

 kept free from the nematode for some twenty years longer. The plant 

 protection services had then become aware of the danger which this 

 disease meant to potato growing and took extensive measvires to control 

 it and to prevent ftirther spread or build up of the nematodes. Con- 

 trary to the situation in England and Germany in the beginning of the 

 20th century, the infested area at the time the disease was recognized 

 in the Netherlands in 19U1 was still so small there that forbidding 

 Che growing of potatoes and tomatoes on or moving plants or soil from 

 infested fields could be considered reasonable measures to prevent 

 further spread. Moreover the famers are not allowed to grow potatoes 

 in non-infested fields oftener than once in three years. 



Control by nematicides is too expensive but the breeding of re- 

 sistant varieties of the potato shovjs good promise. 



Contrai:y to the potato cyst eelworm, the beet cyst eelworm seems 



