Published 02.02.2026

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Prevention of oat cyst nematodes

Oat cyst nematodes and the preventive measures against them should receive particular attention in organic farming, where spring cereals make up a large scale of the crop rotation

By Tove Mariegaard Pedersen

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Oat cyst nematodes - damage and symptoms

Damage caused by oat cyst nematodes is mainly seen in spring cereals. Oats are affected the most, followed by spring wheat, and finally spring barley, which is the least affected. There are resistant varieties of oats and spring barley that do not form cysts. Resistant oats are still attacked by nematodes and suffer damage simlar to susceptible oats, while resistant varieties of spring barley are less affected during infestation in the field. However, resistant varieties plau an important role in reducing the level of infectation in the field.

Severe attacks appears as patches of poor crop growth in the field.

Patchy infestations of oat cyst nematodes (here in conventional field).

Growing conditions in a given year influence the extent of damage. Damage is more visible under poor growing conditions, such as cold and wet springs, which favour the nematodes and slow plant growth, followed by dry summers, when the damaged roots cannot absorb enough water. Infestations may be more pronounced in light soils, and attacks can therefore sometimes appear as stripes in the field. Heavily infested plants compete poorly with weeds, and increased weed occurrence may be seen in patches. In oats, symptoms may include reddish leaf tips.

Oat cyst nematodes can cause short, strongly branched and thickened roots in oats. Small cysts (about 0.7 mm) form on the roots and can be seen from mid-June.

Healthy plants are shown on the left, and oat plants with infected roots are shown on the right. The infected roots become short, thickened, and highly branched. The plants on the right have been stained with iodine in the laboratory to demonstrate the presence of nematodes in the roots.

The photos show cysts of the oat cyst nematodes Heterodera Avena, races I and II.

Two brown cysts on the "beard".

Cysts on roots.

White cyst on root.

Brown cyst of race II with oval eggs.

Life cycle and propagation of oat cyst nematodes

The risk of propagating oat cyst nematodes is greatest when growing a crop that is a good host plant for the nematodes. If a "good" host plant is grown, the nematode population can increase by up to about 50 times within a single year.

The annual cycle of oat cyst nematodes.

Oats and other spring cereals are the best hosts for oat cyst nematodes, although resistant spring barley is a less suitable host. After spring cereals, winter wheat is the next best host and can increase nematode populations, but it is usually less affected than spring cereals because its root system is more developed in spring. Winter rye is a poor host. Maize can be attacked when the infestation level is high, but it does not increase the nematode population. Several grass species can also serve as host plants and maintain the infection level, although they are not damaged by the nematodes.

Yield loss caused by oat cyst nematode

In Sweden, a relationship has previously been found between the number of eggs in the soil and yield loss, although with considerable variation due to differences in growing conditions. As shown in the table, the lowest damage threshold has been found in oats and spring wheat at fewer than 1,000 eggs per kg of soil, and in susceptible spring barley and winter wheat at fewer than 3,000 eggs per kg of soil. In resistant spring barley, the threshold is below 30,000 eggs per kg of soil.

Under very severe infestations of 30,000 eggs per kg of soil, yield losses of up to 25–40% in oats and spring wheat have been observed.

Table: Average yield losses caused by oat cyst nematode (Swedisch data)

m = susceptible, r = resistant.

Eggs per kg soil	Oats (m+r) and spring wheat	Spring barley (m) and winter wheat	Spring barley (r)
1.000	2-5	0	0
3.000	5-10	2-5	0
10.000	15-25	5-10	0
30.000	25-40	10-15	2-5

Variety choice and crop rotation are crucial for prevention

Variety choice and crop rotation can help prevent problems with oat cyst nematodes. Resistant cereal varieties and crops that are not host plants can reduce the infection pressure by about 40–60% per year, because they do not form cysts.

Crops that are not susceptible to oat cyst nematodes include:

oilseed rape
peas
potatoes

Resistant varieties of oats and spring barley are available on the market, although the selection of resistant oat varieties is still limited. However, several breeders have begun to prioritize this trait in breeding programmes. Even though resistant oat varieties can suffer damage similar to susceptible varieties, they still play an important role in reducing nematode pressure in the soil.

If you suspect a high level of oat cyst nematodes in a field, you should take a soil sample (at least 50 cores) in autumn and have it analysed (this type of analysis is offered, for example, by Eurofins). If the analysis shows more than 1,000 eggs per kg of soil, oats, spring wheat and susceptible spring barley varieties should not be grown. The higher the number of eggs and larvae, the more years crops that are non-hosts or resistant varieties must be grown before the nematode population is reduced to an acceptable level.

Oat cyst nematodes also have natural enemies, including parasitic fungi and predators. This may be one reason why infestations are not always predictable in the field. Maintaining healthy soil with rich soil life is always beneficial, but this should not be the only preventive strategy.

Infection tests to assess nematode resistance

Tests for nematode resistance are carried out in Denmark as part of the official value testing of spring barley, spring wheat and oats conducted by TystofteFonden.

The infection test involves exposing plants to infested soil for one growing season (April–August) in outdoor nematode pits. The plants are grown in PVC tubes, and their roots are later examined for the number of cysts.

This is a comprehensive and time-consuming test, in which resistance to both Heterodera avenae race I and II is assessed. Information about the susceptibility or resistance of varieties can be found in SortInfo.

Nematode resistant varieties on the market

Among cereal species, nematode-resistant varieties of spring barley and oats are available. All spring barley varieties included in organic variety trials in 2025 were resistant, except Laureate.

Currently, Dominik, Nemesis and NOS Conrad are the only commercially available oat varieties with resistance to oat cyst nematodes, although more new varieties may soon become available.

Dominik, developed by the German breeding company Saatzucht Bauer, has been included in Danish variety trials since 2004. In the past five years of conventional trials, yields have ranged from index 90–96.

In organic variety trials, yields have varied between two very different growing seasons: index 86 in 2025 and index 107 in 2024.

Nemesis, maintained by Lantmännen in Sweden, has achieved yield indices of 95–98 in five years of conventional trials. In organic variety trials, Nemesis produced index 78 in 2025 and index 95 in 2024.

New breeding programme focusing on nematode resistance

Nordic Seed has launched a new oat breeding programme that also targets organic growing conditions and resistance to oat cyst nematodes. New resistant breeding material is expected from this programme. The programme also selects for plant height and powdery mildew tolerance. Other breeders in the Nordic countries and Germany have also initiated new activities focusing on nematode resistance in oats.

Organic variety trials with nematode-resistant oats in 2024-2026

The Innovation Centre for Organic Farming conducted organic trials with resistant oat varieties and breeding lines in 2024 and 2025, and further trials will also take place in 2026. There is a need to develop new resistant varieties, and therefore new breeding material from Germany and Sweden is being tested.

In 2025, three trials were conducted, which also functioned as variety trials including company-submitted varieties without known resistance. The varieties Caledon, Scotty, and the nematode-resistant breeding line NOS 82110-20 produced the highest yields, while the resistant variety Nemesis had the lowest yield and the most weeds.

Yields in the trials were generally high, which can likely be attributed to early sowing.

The breeding line NOS 82110-20 appears to be a promising candidate with nematode resistance, high yield, low disease pressure, and high thousand-kernel weight. Results from the trials can be found in SortInfo and Landsforsøgene 2025. The breeding line NOS 82110-20 will also be included in organic trials in 2026, together with several other breeding lines from three different breeding companies.

When choosing an oat variety, emphasis should be placed on high and stable yield, good disease resistance (especially to powdery mildew and oat leaf blotch), nematode resistance and strong straw. For oat production for groats, important characteristics include high test weight, low hull content, and good dehulling ability.