DISEASE TESTING OF CEREALS
Micro-organisms may develop on seeds in field crops before harvest. Colonisation of the developing seeds depends on the climatic conditions, the presence of an inoculum source and the susceptibility of the crop. Fungi that establish on the developing seed in the field may be broadly of two kinds:
- Saprophytic field fungi
- Pathogenic fungi
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 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 effect 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 seed if it has not been tested.
The requirements of farmers for disease testing depend on a number of factors, details of which are listed below:
Barley Leaf Stripe
In our view the 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 with reduced rates of fungicide.
- You intend using a treatment that does not control leaf stripe, or only provides partial cover
Barley Loose Smut
Similar criteria apply to the need for testing barley for loose smut:
- If smutted heads were seen in the mother crop, or neighbouring barley crop
- If the seed is to be sown untreated, or you intend using a seed treatment that
does not control loose smut or gives limited control.
Seedling blight in Wheat and Oats
Microdochium nivale (Fusium nivale) is the major cause of seedling blight in the UK. Wheat or oat seed should never be sown untreated without first testing the seed for germination and Michrodocium nivale. Barley is much less susceptible and seed borne Microdochium nivale infection has relatively little effect on barley seed germination.
Trials suggest that seed with infection levels of up to 10% Microdochium nivale can be sown untreated
A word of caution- try to avoid using reduced rates of treatment on winter wheat seed that has more than 10% 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 bunt in winter wheat crops. Bunt is a very damaging disease that can reduce yields and grain quality, particularly for milling. Severely infected crops are still rare in the UK. Such crops are likely to have been farm-saved and sown untreated for a number of years. We advise a threshold of 1 spore per seed above which the seed should be treated. If you intend to sow winter wheat seed untreated, or with reduced rates of treatments, it is important to have the seed tested.
Acknowledement: Valorie Cockerell, Official Seed Testing Station, Scotland