568 



Baunacke (W.). Untersuchungen zur Biologie und Bekampfung des 



Rubennematoden Heterodera schachtii, Schmidt. [Investigations 

 into the Biology and Control of the Beet Nematode, H. schachtii.'] — 

 Arb. Biol. Reichsanst. Land- ii. Forstw., Berlin, xi, no. 3, 1922, 

 pp. 185-288. 5 plates, 2 tables. 



Nematode infestation is of great economic importance in Germany 

 because of the too intensive cultivation of beet, and because Heterodera 

 schachtii, Schmidt, threatens to spread to other valuable field crops. 

 A comparatively simple and rapid method of ascertaining the presence 

 of Nematodes in soil consists of determining the cyst content of the 

 ground at various depths. The upper 12 in. of the soil provide the 

 Nematode with the most favourable conditions for most of the year, 

 but in heavily infested fields cysts may be found down to about 

 32 in. below the surface. The deep-lying cysts are responsible for 

 lasting infestation, while those near the surface serve to spread and 

 rapidly increase the pest. To obtain soil samples, trenches about 

 39 in. deep are dug in various parts of the field. Samples of soil taken 

 at 16 in. are mixed together, and a sample is spread on paper and 

 allowed to dry for a day. It is then placed in a dish, and after sufficient 

 water to reach the edges of the dish has been added, the whole is stirred 

 and allowed to stand. The brown cysts then appear at the surface, 

 though later on they sink. Samples of soil are also taken from the 

 trenches at other depths and treated in the same way. 



The larvae that hatch from the cysts make their way to the food- 

 plant, and this habit permits the use of simple baits to ascertain their 

 presence and to test the effect of remedial measures. A bait is 

 prepared by placing about 3i oz. of sand (washed quite clean) on a 

 piece of rag 6 in. square. About | oz. of beet seed is placed on the 

 sand and the corners of the rag are gathered up and tightly bound 

 round the end of a stick, sufficient space being allowed in the bag thus 

 formed to permit the seed to swell. A number of bags are buried in 

 the field, the projecting sticks indicating their positions. When 

 numerous rootlets penetrate the fabric, the bag must be carefully 

 lifted, freed from all adhering earth and emptied into a clean container. 

 If water is poured on, stirred and passed through a sieve before complete 

 settling has occurred, the sand will remain in the container, the rootlets 

 will be held in the sieve, and the Nematodes can be examined. A 

 general idea of the effectiveness of the bait can thus be gained, but 

 microscopical examination is necessary to differentiate between H. 

 schachtii and other Nematodes. This bait method enables the food 

 preference of the established Nematode strain to be deteiTnined before 

 planting, so that choice in crop rotation can be made accordingly. 



The behaviour of the active larva is governed by chemical and 

 thermal stimuh. The optimum soil temperature is about 25° C. [77° F.]. 

 The larva is guided to its food-plant by its sensitiveness to the water- 

 soluble products of metabolism of the roots of the plant. This 

 sensitiveness becomes speciahsed to the root secretions of a given plant, 

 and the Nematode strains thus formed do not readily attack other 

 plants. The embryo within the egg and the larva lying latent within 

 the cyst are also susceptible to the same stimuli, and by the use of 

 these, cysts can be induced to give rise to larvae in a few weeks instead 

 of in the normal period of a few years. Some few of the descendants 

 of a highly specialised strain of Heterodera remain capable of general 

 adaptation, and ensure the continuance of the species under changed 

 conditions. Measures must be directed against the cysts. As the 



