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In the United Kingdom saprophytic field fungi such as Alternaria, Epicoccum and Cladosporium are common on developing cereal seed and these fungi may discolour the seed. However, they are comparatively short lived in storage and have little effect on either seed germination or on crop performance in the following season.
Seed-borne pathogenic fungi on the other hand may survive for long periods in storage and may attack seedlings during germination leading to poor emergence and a reduced seedling population. They may also be transmitted from the seed to the seedling causing disease symptoms and possible yield loss at a later stage of growth.
Some seed-borne diseases can multiply rapidly from one generation to the next and seed crops can also become infected from neighbouring diseased crops. In this way seed-borne disease can seriously affect the quality of both certified and farm-saved seed.
Seed-borne disease is usually controlled by using appropriate chemical seed treatments and it is extremely inadvisable to sow untreated cereal seed if it has not been tested. In some circumstances the choice of seed treatment may depend on the result of tests for seed-borne diseases. The OSTS offers a full range of seed-borne disease tests. The requirements of farmers and merchants for disease testing depend on a number of factors, details of which are given below for the most frequently requested tests.
Barley Leaf Stripe
In our view barley seed need only be tested for leaf stripe infection if:
* Symptoms of leaf stripe were seen in the mother crop, or in neighbouring barley crops.
* The seed is to be sown untreated, or treated with reduced rates of fungicides.
* You intend using a seed treatment that does not control barley leaf stripe or only provides partial control.
Barley Loose Smut
If any loose smut infection was seen in the mother crop the seed should be tested before decisions are made on chemical seed treatment. Barley seed treatments differ in their efficacy in controlling loose smut and guidance on appropriate seed treatments can be provided by your SAC
adviser or by Valerie Cockerell in the Official Seed Testing Station for Scotland (Phone 0131-244 8900).
Microdochium nivale in Wheat and Oats
Wheat or oat seed should never be sown untreated in Scotland without first testing the seed for germination and Microdochium nivale. Barley is much less susceptible and seed-borne Microdochium nivale infection has relatively little effect on barley seed germination.
The chemical seed treatments available for use on winter wheat all give some control of M. nivale. But they are not all equally effective. Treatments containing guazatine (Panoctine), fludioxynil (Beret Gold) or bitertanol plus fuberidazole (Sibutol) have given better control of the disease than other proprietary treatments, especially where the seed is heavily infected. The OSTS and SAC believe the following guidance may be helpful to producers of winter wheat seed in Scotland and growers who intend to save their own wheat seed:
â?�;It is recommended that all winter wheat seed be treated with a proprietary seed treatment, but in specific cases where this is not possible (ie, seed for organic growers), do not sow winter wheat seed untreated unless the germination is above 90%, the incidence of M. nivale is below 5% and seed bed conditions are favourable for quick establishment.
â?�;6-20% M. nivale - any of the proprietary seed treatments approved for winter wheat (Baytan, Beret Gold, , and Sibutol) should give satisfactory control of the disease.
â?�; 21-35% M. nivale - if the seed is to be sown early, into a good seed bed and quick establishment is expected, any of the proprietary seed treatments available for winter wheat should give satisfactory control of the disease. However, if the seed is to be sown late or is likely to be sown into a cold seed bed that could delay emergence the following seed treatments may be more effective: Beret Gold, Panoctine, or Sibutol.
â?�; More than 35% M. nivale - Panoctine, Beret Gold or Sibutol may be most effective, especially in cold seed beds where emergence is delayed.
A further word of caution - try to avoid using reduced rates of treatment on winter wheat seed that has more than 20% M. nivale infection. Also be aware that a reduced rate tested against M. nivale may not effectively control other seed-borne diseases or foliar diseases listed on the product label.
Bunt of Wheat
Many growers are concerned about reports of bunt (Tilletia caries) in winter wheat crops. Bunt is a very damaging disease that can reduce yields and grain quality, particularly for milling. In recent years, there has been an increase in the number of bunted crops reported, particularly in England. Severely infected crops are still rare in Scotland. Most of the infected crops have been farm-saved and sown untreated for a number of years. A three year survey of UK cereal seed, carried out at the Official Seed Testing Station for Scotland, has shown that approximately 30% of Scottish winter wheat seed is contaminated with bunt spores at very low levels. If you intend to sow winter wheat seed untreated, or with reduced rate seed treatments, it is important to have the seed tested. If you are concerned or wish further information, please contact Valerie Cockerell, our Seed Pathologist in the Official Seed Testing Station for Scotland (Phone 0131-244-8900). |
