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Stem nematode

Agronomist, Hayden Lunn (Landmark), has reported a large number of canola plants with signs of stem nematode (Ditylenchus dipsaci) infection in multiple crops around Finley, in the Riverina district of New South Wales. The crops range from cotyledon to 8-leaf stage, and Hayden says 5-20% of plants within each paddock appear to be affected. The damage is not particularly severe although typical symptoms are visible including stunted and distorted leaves and stems. Hayden says paddocks sown with a disc-seeder are the worst affected, followed by those that were direct drilled, and paddocks that were cultivated prior to sowing are the least affected.

Stem nematodes are relatively common plant parasites and are widespread in temperate areas of Australia. They have previously been detected in crops in South Australia, Victoria and New South Wales. There are many races of stem nematodes. The ‘oat race’ is one of the most problematic in broadacre crops and known to affect oats, faba beans, field peas, canola, lentils and chickpeas, along with some horticultural and ornamental plants. 

Stem nematodes can tolerate desiccation and they become anhydrobiotic (inactive) in dry soil, hay and seed, sometimes for many years at a time. When significant moisture is available (usually in autumn) they become active again and can invade young growing stem tissues of plants, especially seedlings that are still below the soil surface. Stem nematodes prefer heavier soil types and cooler, moist conditions

Severe cases of stem nematodes can eventually lead to plant death. Some symptoms may be confused with herbicide damage, water-logging or nutrient deficiency. Controlling stem nematodes is difficult once they have invaded plants, so control efforts should focus on rotations involving non-host crops (e.g. wheat and barley) or controlling volunteer hosts in paddocks and avoiding the spread of infested plant material, hay, seed and soil.

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