Crops notes Oct 04

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 7-10 days before ploughing, and an interval of at least 14 days should be allowed between desiccation and sowing. If the "green bridge" has not been destroyed prior to cultivating, then an aphicide approved for BYDV vector control should be applied at brairding.

All cereal crops brairded before the end of October are also at risk, in this case from winged aphids migrating into the crop from nearby fields. These aphids can transmit the virus to the crop directly, but more serious damage often results if these aphids are allowed to reproduce and their offspring spread the virus within the crop during mild winter spells. To prevent this, crops should be sprayed with an aphicide at the end of the migratory period (usually around the end of October). Early sown crops may also benefit from an additional spray before the end of migration.

All crops (even those emerged after the end of October, or previously sprayed) should be monitored for aphids throughout the winter. Inspect on sunny days that encourage the aphids to crawl up the cereal plants and apply an approved aphicide if aphids are found.

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 the aphid migration. Later drilled crops treated with Secur seed treatments will not usually require a foliar aphicide, except if aphid migration extends beyond the first week in November or a low seed rate was used. If in doubt about the necessity to apply aphicides to imidacloprid treated crops, consult your seed supplier.

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 + diflufenican, for example, Panther, or isoproturon + pendimethalin, for example, Encore, is likely to be suitable.

Autumn weed control options for winter oats are limited, but oats are a competitive crop. Leaving weed control until the spring may therefore be an option. If an autumn post-emergence treatment is considered essential, then Lexus Class may be used. However, it has only moderate activity against annual meadow grass.

Growers should aim to drill winter crops as soon as possible to maximise the benefit obtained from good soil conditions. As seedbed conditions deteriorate with later drilling, growers should increase seed rates to allow for reduced levels of crop establishment. Seedbeds should be firmed but not fine to avoid surface capping and ensure good water movement.

Mechanical damage is one of the most important factors affecting potato quality and it is largely controllable. All those involved in harvesting and handling should be trained and encouraged to operate equipment properly and made aware of the importance of damage and bruise prevention. Harvesting and handling systems should be inspected for places where damage could occur, especially sharp edges and large drops.

Other areas where damage regularly occurs include 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. Bruising can be easily identified by placing a sample in a polythene bag in the hotpress for 48 hours. This accelerates the development of a visible bruise - blackening of the flesh in the damaged area.

Excessive damage will lead to increased problems in store and eventual down grading of the produce. Extra care will be needed at later harvesting dates as cold potatoes damage more easily.

To prevent the development of skin blemish diseases and soft rots, tubers should be dried as quickly as possible after lifting. Drying within 48 hours using positive ventilation systems has been shown to significantly reduce the development of 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 12-15ºC and 85% 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.

DARD Farm Management Notes for October 2004 have been prepared by Greenmount Campus, College of Agriculture, Food and Rural Enterprise - Tel: 028 9442 6771. We acknowledge the contribution from Veterinary Service. For further information contact your local DARD Development Adviser.