Soil populations of beet eelworm (Heterodera schachtii Schm.) in relation to cropping
Authors: Jones F. G. W. 
Published: February 2008

Between 1934 and 1936 beet eelworm was found to be prevalent on a farm in the Isle of Ely. The virtual absence of other species of Heterodera and the workable nature of the soil made the farm ideal for the study of soil populations. In 1937 a sampling technique for estimating the cyst, viable cyst and egg content of soil was developed and standardized. The first part of the paper deals with the sampling technique and the investigation of the various steps of which it is composed. When put into operation, the technique gave consistent results, but difficulty was experienced with counts of viable cysts and eggs owing to bias between different observers.

The second part of the paper gives the results obtained by the application of the technique to twenty‐four fields during the period 1937‐42. There appears to be a correlation between the general level of the eelworm population and the frequency with which susceptible crops are grown, and also between the general level of the population and the amount of damage to the crop, ‘beet sickness’ being most extensive and most severe where populations are greatest. Marked increases in the eelworm population follow the planting of susceptible crops upon heavily infested land, while smaller increases occur in fields with low eelworm populations. Fields which were completely ‘beet sick’ required very long periods of rest from susceptible crops (more than 10 years) before the eelworm populations in them fell to a low level and before they could be regarded as safe to grow sugar beet once more. The general effect of non‐susceptible root crops is to bring about a lowering of the eelworm population. Cereals have the same general effect, but to a lesser extent. In some instances, rises were recorded after the growing of cereals. These appeared to be due to weeds, or to susceptible crops growing as weeds amongst the cereal crops. Claying had a beneficial effect.

The results of the investigation indicate the difficulties which may arise where close cropping is practised with crops susceptible to beet eelworm, and the desirability of avoiding widespread ‘beet sickness’ in important beet‐growing areas. Brassicae are capable of increasing beet‐eehvorm populations, although they do not as a rule show signs of distress when growing on land where sugar beet develops the symptoms of ‘sickness’.

A strong correlation was observed between the viable cyst and egg content of bulk samples. This suggests that viable cysts are a better measure of the general level of the eelworm population than might have been supposed. Cysts decay slowly and remain in the soil long after they are devoid of living contents. For this reason cysts alone are better as a guide to the past history of an infestation than as a measure of its present intensity. The eehvorm population of any field is complex and has highly individual characteristics. The best measure of this population so far devised is an estimate of the encysted egg population. While this may be adequate where it is desired to note changes in the level of the population following a particular crop or treatment, it is not nearly so satisfactory where a forecast of damage to an ensuing crop is required.

In examinining cysts for viability, fungal hyphae and the fruiting bodies of other organisms were found inside. One of these, a fungus of the Order Chytridiales, had fruiting bodies similar to microcysts (Triffitt, 1935), and it is concluded that some part at least of the microcyst population of soils is composed of the fruiting bodies of fungi of this Order. Another organism, probably a fungus, caused blackening of the eggs. This was almost certainly a parasite, and its rather high incidence suggested that it might be of importance in reducing egg populations.

In conclusion, a number of suggestions are made for the adaptation of the technique for advisory purposes. Experience suggests that the general level of the egg population above which it is unsafe to grow sugar beet or mangolds on Fen soils is about 10 eggs per g. of air‐dried soil or approximately 0.1 viable cysts per g.