Why buying new seed is important to an organic farmer…

It is estimated that approximately 60% of C2 certified combinable crop seed used in the UK is farm saved seed. Now this is ok, as long as the seed is thoroughly tested for germination, vigour, inert matter, moisture and most importantly for an organic farmer, diseases.

If you are home saving, we advise that seed is tested for the following classical seed borne diseases;

Microdochium Nivale (a form of seed borne Fusarium affecting wheat, barley, oats, triticale and grasses)

Microdochium-NivaleThis fusarium causes seedling blight resulting in seedling death and thinning of the plant stand. The most important source of fusarium for wheat crops is the seed but the fungus can also survive in debris in the soil, stubble and volunteers.

Symptoms include lesions on the stem base, which spread up the leaf sheath. Infections can result in all or part of the ear becoming bleached with loss of yield. Infections later in the growing season cause mycotoxin production in the grain.

This disease can often controlled by seed dressing but in an organic situation this has to be managed by rotation, clean seed and the timely sowing of crops.

Bunt (otherwise known as stinking bunt, specific to wheat)

BuntThis is disease is very rare in the UK as the vast amount of seed is treated with a fungicidal seed treatment, however for organic farmers it is vital that you check your farm saved seed for this disease as results can be devastating and cause whole crops unsalable due to the fishlike smell and discolouration of the grain.

It is recommended not to use seed with more than one spore per seed, but proper sampling is absolutely vital when testing seed you wish to home save. The HGCA project 2112, showed that it took 40 samples from one heap to detect bunt at a level of 25 spores per seed as it can sit in certain areas of the heap and not always be picked up from one sample.

If a small amount of bunt is present in the seed, it is advisable to only use that seed for one year and renew your seed the year after if you are not able to use a seed treatment. The table below demonstrates the increase in infected plants from home saving seed with bunt for one to three years.

Bunt (% plants infected)
Year 1 0.01
Year 2 0.2
Year 3 25

Loose Smut (affects wheat, barley and oats)

Loose SmutEasily recognisable at ear emergence as each grain is usually completely replaced by a mass of black fungal spores. Spores are released from infected ears and carried in the wind. Weather conditions during flowering affect the length and time that the florets remain open and hence the time that the plant remains susceptible to infection. Therefore infections varies from year to year depending on weather conditions.

The fungus lies dormant in the embryo of the seed until the seeds are sown and germinate. The UK has extremely low levels of loose smut and this is undoubtedly due to the stringent guidelines of the seed certification scheme.

Leaf Stripe (specific to barley)

Leaf StripeLeaf Stripe is a seed borne disease causing long brown stripes on the leaves which start off pale green, turning yellow and then finally dark brown. The disease is most severe on crops which have been grown from untreated seed.

Leaf Stripe can affect the plant in three ways… First it can kill seedlings as they emerge. This is unusual but can occur if soil conditions are poor. Secondly it can reduce the efficiency of the plant by reducing green leaf area and finally it can result in complete blindness of the ear resulting in no harvestable grain from affected tillers.

Potentially the most serious seed borne disease for barley and if seed from affected crops are re-sown without an effective fungicidal treatment being applied the disease can multiply significantly and produce large yield losses. If seed is saved and re-sown repeatedly, complete crop loss is possible within a few generations of seed multiplication. The table below shows demonstrates this;

Leaf Stripe (% seeds infected)
Year 1 0.01
Year 2 0.6
Year 3 36

 

Net Blotch

Net BlotchNet Blotch is now a very important disease of barley and can cause large losses where the disease is not controlled. However the seed borne phase is relatively unimportant compared with trash borne and has little threat on yield.

Infection of young seedlings with net blotch can look very similar to leaf stripe infection with the first leaf often showing a single brown stripe extending the whole length of the leaf.

More recently identified seed borne threats include:

Rhynchosporium

RhynchosporiumThis disease affects barley, rye and triticale mainly and is seen in the South and South/West where conditions are often wet and mild. The most serious effect on yield in both winter and spring barley results from attacks that develop between first node detectable and boot swollen growth stages.

The fungus is seed-borne but the importance of this phase of the disease is not fully understood. The most important source of the disease is probably crop debris from previous crops and volunteers which become infected from the stubble from previous crops.

Ramularia

RamulariaRamularia can be detected on the seed and is an extremely important barley disease to understand as it can cause extensive damage to the upper leaves in spring and winter barley once crops have finished flowering. The disease can also be dispersed via air-borne spores and symptoms can develop on dead lower leaves but symptoms are rarely seen on healthy green leaves until after flowering. This can cause extensive losses in yield and quality. Yield losses in spring barley can be up to 0.6 tonnes per hectare.

Typical symptoms of Ramularia comprise small brown rectangular lesions, often surrounded by a yellow halo. They resemble the spot-form of net blotch. Following high levels of infection, the leaves may senesce rapidly. Lesions are often obvious on dead leaves as black spots.

Tan Spot

Tan SpotTan Spot affects wheat but can also attack barley, rye and some grasses. Tan Spot is very common in Scandinavia and parts of France but is still rare in the UK. Although it is occasionally recorded in disease surveys it rarely causes serious losses on individual crops grown under minimum tillage systems. However there are a few isolated cases where the disease has caused serious losses.

Tan Spot is a seed borne disease which infects seedlings, resulting in small tan to light brown flecks on young leaves. However, symptoms are generally seen later in the season in the middle and upper canopy. Early symptoms of infection are small tan to light brown flecks, with a chlorotic halo, often with a dark spot at the centre. Later these develop into light brown oval lesions with slightly darker margins with a light coloured spot at the centre.

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Wheat farming through the ages
Spring wheat vs. winter wheat