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Swedes serve as winter feed for livestock. Swedes thrive best in cooler, moist conditions and dislike waterlogged areas and dry spells. For best growth, avoid soils that are either too light and drain quickly or too dense and retain too much water. Swedes face diseases like club root and dry rot, which limits them to first-year cropping after any brassica crop. There are early and late maturing swede types, each with unique characteristics. Yield depends on soil type, disease, and moisture but typically falls between 12-16 t DM/ha. They store well over winter, offering a high energy value. Proper soil preparation, specific sowing techniques, and appropriate fertiliser applications enhance yield. Watch out for diseases, pests, and weeds. Swedes caused health issues in cows in 2014, so follow recommended guidelines when feeding them to your livestock.
Swedes are normally used as a winter feed crop. As they have a low tolerance to drought, swedes perform best in cooler, moist environments, however they do not like waterlogging.
To maximise yield, avoid light soils with low water holding capacity or heavy, poorly drained soils. Swedes are susceptible to club root (soil borne) and dry rot (air borne); these diseases mean they can only be a first year cropping option. Never establish swedes as a second crop after any other brassica crop.
There are two types of swedes:
The yield will vary depending on soil type, fertility, disease, and available moisture. Yields of 12-16 t DM/ha can be achieved under good growing conditions in southern areas. Swedes are usually grazed from early to late winter, with bulbs usually keeping well through the winter unless diseased. However, swede yield commonly declines during winter because of adverse weather and disease damage.
The energy value is high, and is held in a form that keeps well over winter. Feed quality testing will often show swede leaf and bulb to have an ME of 12.5 MJ/kg DM or more.
To maximise yield, a fine, firm, moist seed bed with good soil-seed contact and uniform plant population must be established. There are four methods generally used:
The sowing rate for each method is:
The optimum sowing depth is 1-1.5 cm in for all the methods. If done correctly, the sowing method does not affect yield. Ridging is typically used for swede cultivation in Southland, as it provides better drainage. However, it is less reliable in drier conditions, where seeds or plants could dry out on top of exposed ridges. Ridging also allows for inter-row mechanical cultivation for weed control.
Swedes should ideally be established between mid-November and the end of December. Problems with dry rot are tending to push the sowing date out to later in December; this can reduce potential yields. Sowing too early can result in vernalisation – where plants experience a cold snap and are stimulated to go to seed prematurely.
Land management guides for good environmental practice and cultivation tips to reduce overland flow and soil erosion are available here.
Swedes respond strongly to N application; it is advisable to do an available soil nitrogen test before sowing to determine how much will be needed.
Depending on soil moisture levels and potential crop yield, a typical recommendation for swedes is 250-350 kg DAP/ha at sowing, followed by a topdressing of 50 - 100 kg urea/ha.
While the requirement for P is quite low, sufficient P is vital for the establishment of seedlings. The P requirement for a second crop is likely to be higher. The ideal pH is 5.8 to 6.2; this should be corrected with lime a year before sowing. Swedes seldom respond to S or K fertiliser.
Swedes have a high boron requirement. Basal applications of up to 1.5 kg B/ha can help reduce the incidence of hollow heart.
The soil type and its potential yield must be considered when applying fertiliser. Following fertiliser recommendations based on a soil test remains best practice.
The main threats are the fungal diseases club root and dry rot, and aphids. Cultivars vary considerably in tolerance to these problems; this affects which cultivars should be grown in a district. Sowing a second crop of swedes in the same paddock is not recommended because it maximises the conditions for fungal diseases to develop, which can significantly affect crop health. Paddocks that have been planted to brassicas and re-grassed must not be returned to swedes within a 5 to 6-year period.
The main insect pest are springtails, diamondback moth, white butterfly, and aphids. Nysius fly can cause major problems by allowing dry-rot (black leg) to enter; this causes weak bases in the plants. Inspect young crops regularly by walking well into the paddock and if necessary, apply the appropriate insecticide. If the spray and drill method is being used, slug control and checks for grass grub and porina are recommended, as these pests can cause the death of new seedlings.
Swedes are especially susceptible to weeds and pests during early crop development so ensuring a good start for the crop is essential. Spray applications prior to sowing depend on the method of establishment. Always use certified seed to reduce the risk of introducing weed species to your farm.
An investigation into why cows became ill or died after eating swedes in the winter of 2014 found it was the result of liver damage, possibly caused by higher levels of certain nitriles. These compounds can be formed as breakdown products following the consumption and digestion of glucosinolates (GSL) found in all brassica species. For more information on the key findings see Swede Advisory.
For advice of feeding swedes to cows
It is still safe to use swedes, but DairyNZ recommends the following: