Major type differences exist in terms of growth behaviour in the case of some varieties used for catch crop cultivation. For mustard and oilseed radish in particular, the Federal Plant Variety Office (Bundessortenamt) recognises clear differences in their initial development and inclination to flower, as well as in their behaviour with respect to beet cyst nematodes (mustard and oilseed radish) and root knot nematodes (oilseed radish). These variety differences are of great importance for the use of mustard and oilseed radish varieties in the various crop rotations.
Mustard and oilseed radish varieties in sugar beet crop rotations
Beet cyst nematodes (Heterodera schachtii) can cause major damage in intensive beet cultivation. If the damage threshold is exceeded, yield losses are quickly in the double-digit percentage range. Cultivating resistant mustard and oilseed radish varieties enables the beet cyst nematodes to be combated biologically and the nematode population in the soil to be reduced. The resistant varieties are split into two categories in this respect.
Varieties with characteristic ranking 1 have the greatest resistance and, in pot trials by the Bundessortenamt, were able to reduce the propagation rate of the nematodes by > 90% (oilseed radish varieties only), while resistant varieties with characteristic ranking 2 were able to reduce it within the range of 70 to 90% (mustard and oilseed radish varieties). In addition to this resistance characteristic, the longest possible vegetative growth phase – which is only achieved by sowing at the right time and with a low inclination of the variety to flower – is important to the control success.
Mustard and oilseed radish varieties in maize and grain crop rotations
Having been taken into account for some time in sugar beet and potato crop rotations due to phytosanitary aspects, the specific properties of mustard and oilseed radish varieties are also of considerable importance for successful catch crop cultivation before maize. Crucial here is not the effect with regard to diseases or pests, but the growing behaviour described by “inclination to flower" and "mass creation at the beginning".
Pronounced initial mass creation with the mustard and oilseed radish varieties used ensures – due to rapid growing – quick closing of rows and thus optimal weed suppression and tolerance for late sowing. The inclination to flower must be considered differently with regard to mustard and oilseed radish. A low inclination to flower, in other words relatively late flowering, combined with rapid initial development, is considered a very positive thing for mustard varieties. The plants quickly generate very leafy foliage and display maximum competitiveness. In the case of the oilseed radish varieties, on the other hand, a greater inclination to flower in cultivation before maize is advantageous. Late-blooming oilseed radish varieties have a tendency towards radish creation if the sowing density is insufficient, which boosts winter hardiness and herbicide tolerance. These then have to be cleared with greater effort after mild winters.
The earlier inclination to flower of the oilseed radish means that the plants start to develop shoots more quickly and grow faster, particularly when mixed with a competitive mustard variety. Due to the widespread suppression of radish creation, the plants are more likely to freeze and are easier to control in the subsequent culture. To create this effect, besides choosing the right variety it is important to have a sufficient crop density that can be guaranteed only by maintaining the recommended sowing density.