In the Indonesian highlands, many temperate vegetables such as cabbage, Chinese cabbage, cauliflower, potatoes, and carrots are intensively cultivated throughout the year. Because of the relatively advantageous climate condition, highland farmers are able to grow lucrative temperate vegetables continuously and/or in high frequency cropping. However, this has led to the incidence of continuous cropping injuries such as the clubroot disease of crucifers.
Cabbage, carrot, and potato can be easily grown three times a year under sufficient soil moisture condition in the tropical highlands, but if these crops were grown continuously, soil-borne diseases such as clubroot and bacterial wilt will break out.
Crop Rotation
Clubroot damage can be minimized by adopting a one-year cabbage-carrot-potato crop rotation scheme
( Fig. 1). Insertion of one fallow cropping during the dry season to this crop rotation scheme makes the control of clubroot damage more stable ( Fig. 2). The crop sequence is as follows: cabbage-carrot-fallow, potato-cabbage-fallow, carrot-potato-fallow, and so on.
To suppress the clubroot damage, crop combination can be modified by using lettuce, garlic, radish, leafy onion, tomato, chili and peanut as alternates. The important point is to avoid growing the host plants for at least two seasons.
The outbreak of bacterial wilt in potato also decreased by using this crop rotation scheme. The continuous cultivation of carrot did not show any negative effect, but after the 7th season, the growth was suppressed. This incident was not observed in carrot cultivation under the crop rotation scheme.
Precautions
In cases where the outbreak of clubroot were severe, crop rotation must be intensified by inserting one more non-host plant or fallow.
Because the control of clubroot damage by short-term crop rotation is achieved during the early growth stage, initial growth management must be done well. Although there will be slight clubroot damage at harvesting time, good yield can be expected. Crop rotation must be adopted continuously throughout the following seasons.
Supplemental Practices
The following supplemental practices must be adopted for the stable control of clubroot by crop rotation:
- Mulching with plastic (transparent) film during the fallow season; and
- Lime treatment at 60 t/ha, four times continuous application throughout the year.
Index of Images
Figure 1 Damages Caused by Clubroot Disease in Continuous Cropping Plot
Figure 2 Effect of Crop Rotation on Vegetable Yield
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