Sanering av betcystnematoder med resistenta mellangrödor

Conclusion

This project showed that it is possible to actively reduce the number beet cyst nematodes in the soil by growing resistant intercrops. For best results the intercrops should be sown as quickly as possible in order to achieve vigorous growth and good root development. If it is possible to utilise nitrogen from the main crop, e.g. peas, this also contributes to good development of the sanitising crop. All trials in this series were sown without prior soil cultivation. The seeds were worked in using equipment available on the farm.
In the investigation we studied:
1. Growth and development of intercrops sown in the autumn.
2. The sanitising ability of white mustard and oil radish from resistance class 1 and 2 when sown as intercrops under Swedish climate conditions.
3. Nitrogen uptake by white mustard and oil radish.
4. The effect of intercrops on the growth, development and yield of the following sugar beet crop (normal and tolerant beet cultivars).
The sanitising effect was calculated as the relationship between the number of nematodes in the spring before sowing of the intercrops (Pii) and before sowing of the sugar beet in the following spring (Pi), i.e. exactly one year later. The mean value of five trials showed the spontaneous reduction in eggs and larvae in the stubble to be 22%. The mean value for class 1 oil radish (cultivar Colonel in all trials) was 29%, that for class 2 oil radish (cv. Cassius) was 42%, that for class 1 white mustard (cv. Achilles/Accent) 38% and that for class 2 white mustard (cv. Maxi/Abraham) 46%. Thus cv. Colonel was the only cultivar that did not exceed 30% sanitisation effect, which was 13 percentage units lower than for cv. Cassius.
At both trial sites in 2007, yield was higher for the normal beet cultivar Rasta than for the tolerant cultivar Julietta, despite the fact that there were nematodes remaining in the soil. For cv. Rasta there were 0.3-2.4 eggs and larvae per gram of soil before the sugar beet was sown, while for cv. Julietta the figure was 0.4-2.3/g soil. The average yield for cv. Julietta (two trials 2007) was 13.82 ton sugar per hectare without sanitisation, 14.17 t/ha for sanitisation with oil radish and 14.24 t/ha for sanitisation with white mustard. The average yield for cv. Rasta (two trials 2007) was 15.82 ton sugar per hectare without sanitisation, 15.19 t/ha for sanitisation with oil radish and 15.48 t/ha for sanitisation with white mustard. The probable reason for the higher yield of cv. Rasta in 2007 was the very rainy autumn, which meant that the sugar beet could compensate for the damage caused by the nematodes. In the other harvest years, 2008 and 2009, cv. Julietta produced higher yields than cv. Rasta at all four trial sites.
From the field trials in this series it was not possible to determine whether there are differences in sanitisation effect between cultivars in resistance class 1 and 2 when they are grown commercially in the field. For oil radish there were indications that cv. Colonel (class 1) had a slightly lower sanitisation effect than cv. Cassius (class 2). The differences may be due to a number of factors, including cultivar characteristics such as flowering ability, early establishment, etc. It was obvious in the trials that cv. Colonel flowered earlier than cv. Cassius, and once the plants had flowered, the sanitising effect declined. This is because the plants reduce their rate of vegetative growth at flowering and do not produce the new, young roots preferred by the nematode larvae. Growers should therefore choose late flowering varieties of resistant intercrops so that the sanitisation period is as long as possible.
Analyses of Nmin when intercrop growth ceased in October showed that there was more nitrogen in the upper 30 cm with oil radish and white mustard compared with the control. However, in the 30-60 cm layer there was less nitrogen left after oil radish and white mustard than in the control.
Dry matter production (kg per hectare) did not vary greatly between the control, oil radish and white mustard. However the amount of root dry matter was somewhat greater for oil radish and white mustard than for the control. A plant that does not receive sufficient nitrogen responds by producing more roots, which was confirmed by the results of this investigation. In order for a catch crop to prevent nitrogen leaching, it is important that it has a deep, well-developed root system that can deplete the soil profile of nitrogen. It must also have a sufficient amount of green biomass to act as a nitrogen sink.
The number of nematodes was not reduced sufficiently at any of the six trial sites so that a normal sugar beet cultivar could be grown the following year. This emphasises the importance of having a long-term strategy for controlling the number of nematodes on infested fields. A combination of different control measures (e.g. longer crop rotation, repeated sanitisation with resistant intercrops and alternating between beet cultivars with different resistance and tolerance mechanisms), regularly monitored by soil sampling, creates the foundation for sustainable cultivation with consistent yields.