Crops notes September 2007

Harvesting can “make or break” a potato crop. Mechanical damage is one of the most important factors affecting potato quality and is largely controllable. All those involved in harvesting and handling should be made aware of the importance of damage and bruise prevention. Damage can occur with drops from harvesters into boxes or trailers, bruising caused by insufficient soil on the web, and crushing due to oversize tractor tyres running in the drill bottom.

Early identification of damage can save substantial amounts of money in terms of reduced waste and rejections. Samples of the harvested crop should be taken daily, washed and inspected for damage. Excessive damage often leads to increased problems in store and eventual down grading of the produce.

Aim to dry your potatoes as quickly as possible to prevent the development of skin blemish diseases and soft rots. Drying within 48 hours using positive ventilation systems significantly reduces the development of diseases such as silver scurf.

The curing period immediately following harvest, often referred to as the ‘wound healing period’, is one of the most important storage phases. Wound healing occurs most rapidly at high temperatures and high humidity. However, these conditions also favour the development of rots and skin diseases. Maintaining the crop at 12 to 15 Centigrade and 85 percent relative humidity for a period of about two weeks, often referred to as ‘dry curing’, allows wound healing to take place, whilst minimising the risk of disease development. Ventilating the store on dry afternoons during the curing period will normally provide suitable conditions for this to take place.

Care should be taken to control aphids that are the vectors of Barley Yellow Dwarf Virus (BYDV) as this disease can cause high yield losses in autumn-sown cereals.

Crops following grass, weedy stubbles, or set-aside are particularly at risk from wingless aphids moving directly over this ‘green bridge’ of grass onto the young crop. To prevent this, the "green bridge" should be destroyed by desiccation with paraquat or glyphosate 7 to10 days before ploughing. If the "green bridge" has not been destroyed prior to cultivating, then an aphicide approved for BYDV vector control should be applied at brairding.

The insecticide seed treatment imidacloprid (found in Baytan Secur, Sibutol Secur and Raxil Secur) can provide protection from BYDV in the weeks immediately after sowing. Earlier sown crops and crops sown at lower seed rates will need a follow-up spray at the end of November.

For effective weed control, a herbicide with contact and residual action should be applied to wheat and barley crops while weeds are small. Annual meadow grass in particular is difficult to control once it has begun tillering. The choice of herbicide treatment may be influenced by the weed species present, but a broad-spectrum product based on either isoproturon plus diflufenican, for example, Panther, or isoproturon plus pendimethalin, for example, Encore, would be suitable.