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.
What type of swedes should I plant?
There are two types of swedes:
- Early maturing cultivars have yellow-fleshed soft bulbs with low dry matter and less disease tolerance. These are suitable for young stock and table swedes for human consumption.
- Late maturing cultivars have both yellow and white-fleshed varieties available. Late maturing types have higher dry matter content, are harder, and keep better into late winter.
What is the typical yield for 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.
What is the energy value of swede?
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.
How should I prepare the soil to maximise yield?
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:
- Normal cultivation with seed broadcast, harrowed and rolled
- Normal cultivation with seed conventionally drilled
- Normal cultivation with swedes sown on ridges
- Spray and drill with zero tillage
The sowing rate for each method is:
- Drilled with 15 cm rows – 0.1-1.0 kg seed/ha
- Ridged - 0.5-0.7 kg seed/ha
- Broadcast & rolled – 1.0-3.0 kg seed/ha
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.
Wintering in southland and South Otago is a land management guide to good environmental practice and has cultivation tips to reduce overland flow and soil erosion.
Guides for other regions are also available here.
What fertiliser should I apply?
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.
What pests, diseases, and weeds should I look out for?
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 - see Farmfact 1-76 for details. Always use certified seed to reduce the risk of introducing weed species to your farm.
What caused the Southland and South Otago 2014 swede disease outbreak?
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
Lessons on the swede outbreak
- Tech Series (Mar 16) - Lessons from swede disease outbreak
- Swede associated toxicity in dairy cattle during winter 2014
From the findings of the swede disease outbreak, are swedes safe to feed my cows?
It is still safe to use swedes, but DairyNZ recommends the following:
- Be cautious when grazing animals on swede crops in autumn before the first frosts, as they may eat more leaves than bulbs as the bulbs are hard and difficult to eat.
- Be cautious, at any time during the season, when grazing animals on swede crops with a high leaf to bulb ratio as cows may preferentially graze leaf.
- Observe the physical characteristics of the crop being fed, monitor the health of cows, and adjust their feed management if ill-health is observed.
- Do not feed swede crops in their reproductive growth phase, which can be recognised when the stem of the swede elongates, new growth appears and the swede plant develops flowers and a seed head.
- Do not feed HT® swedes on the milking platform in late August/early September (i.e. late pregnancy, early lactation). This period is when many of the factors that lead to ill-heath and potential cow death (warmer temperatures, new leaf growth, bolting) can rapidly combine.
- Follow PGG Wrightson Seeds advice regarding HT® swedes and their use.