Crops notes October 2006

Annual meadow grass is a difficult weed to control once it has begun tillering in wheat and barley. 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) or isoproturon + trifluralin (for example. Autumn Kite) are 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.

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. All cereal crops brairded before the end of October are also at risk, in this case from winged aphids migrating into the crop from other 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 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.

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.

Winter cereals have a great capacity to produce tillers.  The earlier a crop is sown the greater the number of tillers produced. This means that there is little variation in ear numbers at harvest between crops sown early at low seed rates and high seed rate and consequently little variation in yield.  

For winter wheat and barley the ideal plant population in the spring should be between 250 to 300 plants per m².  This should result in between 600 to 700 reproductive tillers per m², giving the optimum combination of yield and grain quality

The optimum plant population is converted to the appropriate seed rate taking account of:

Thousand Grain Weight (TGW)

germination percentage of the seed lot sown  

estimated percentage establishment

The following formula is used:

Seed rate (KGs/ha)=    (Target plant population (plants/m²) x 100)x TGW(g)                                                                              (Percentage germination x Percentage establishment)

(To convert from KGs/ha to st/acre: multiply KGs /ha by 0.064)

(To convert from st/acre to KGs/ha: multiply st/acre by 15.72)

Under appropriate conditions growers should reduce winter cereal seed rates to 126-173 KGs per hectare (8-11 st/acre) from traditional rates of 157-204 KGs per hectare (10-13 st/acre).

Mechanical damage reduces potato quality and is largely controllable. It is important that all operators involved in harvesting and handling should be trained to operate equipment properly to minimise damage and bruising. Harvesting and handling systems should also be inspected for areas where damage could occur, especially the alignment of the share to the primary web, at haulm separation, sharp edges and large drops.

Samples of the harvested crop should be taken daily, washed and inspected for damage using the ‘hotbox’ technique. This involves putting a sample of tubers in a polythene bag and placing them in a domestic hot press for 24- 48 hours. These conditions accelerate bruise development, which is clearly visible as blackening of the flesh in the damaged area.

Extra care will be needed at later harvests. Make every effort to maintain a good soil cushion on the main web of the harvester, minimize agitation and reduce drop heights.

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 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.