Seed- and soil- borne diseases

A disease specific to wheat, bunt is well-known for smelling of rotting fish. The disease replaces the grain in infected ears with balls of spores. When these balls are ruptured by the combine, the spores are released as a sooty cloud, contaminating not just the seed in the combine but also the soil, nearby crops and the grain store.

To spot bunt, you need to look for yellow streaks on flag leaves, and stunted plants with dark grey-green ears and slightly open glumes. Cases of bunt are rare, but usually occur when farm saved seed has been repeatedly sown without a single purpose dressing. The disease spreads very quickly as each bunt ball contains millions of spores. As well as contaminating grain, bunt can also contaminate any machinery or equipment it comes into contact with.

Covered smut primarily occurs in barley. It is usually only found in crops that are grown repeatedly from home-saved, untreated seed.

There are no identifiable symptoms of covered smut until ear emergence. At this time, ears look normal except the grains appear to be covered by a thin membrane. However upon breaking open the membrane it will be apparent that the grains have been replaced by masses of black spores.

These black spores are either released from the membrane and carried by the wind to neighbouring plants, or remain under the membrane, to contaminate surrounding seeds after harvesting. In either case, the spores are then dormant on the exterior of the seed until germination, when they will infect the developing seedling.

Ergot is known well by many growers, likely due to the risk associated with this disease and grain rejections. Ergot replaces the grain in spikelets of wheat, barley, oats, rye or triticale with a hard, dark purple sclerotium. It is the diseased sclerotia themselves that are known as ergots.

Ergots fall to the ground at harvest time, germinating in the spring to give spore producing structures. The spores they produce are released into the air, getting into the open flowers of nearby cereals.

As part of the Fusarium group of fungi causing seedling blight, Microdochium nivale can cause a significant reduction in crop establishment which can lead to a reduction in yield. The disease is most commonly seen in wheat but can infect other cereals too. Infection may be from the soil, but the disease is also seed-borne.

Losses are most pronounced when untreated seed is sown with high levels of infection into poor seedbeds, and with late sown crops. On surviving infected seedlings, the disease splashes up the plant and can cause infection of the ear. Wet weather at flowering can lead to high levels of infected seed.