During 2006 we carried out a bruising survey which highlighted the huge effect bruising and damage can have throughout the supply chain.
In a typical business bruise and damage can cost from £0 to £1,250/ha, but averages at £200/ha (fresh growers estimate £221, processing £161). This is costing growers an estimated £26 million a year, and the whole supply chain in the region of £100 million. Due to the many factors involved in bruise and damage susceptibility and the interaction between these factors, it remains very difficult to develop a measure for bruise and damage potential within a crop. Certain years, such as 2012 where dehydration of the tubers occurred during drought conditions, bruise susceptibility is anticipated to be high.
Bruising or blackspot bruising is caused when the tuber is impacted. The skin doesn’t break, but internal tissues are damaged leading to the formation of the pigment melanin, which will make the damaged area appear black, or dark to light grey. This can be anywhere on the tuber, but is more prevalent at the stolon end, and where the tuber is more curved.
Damage can be divided into internal fissures and crushing when the skin is intact, which can be difficult to see. Splitting and cracking occurs when the skin breaks and internal tissues are visible. If the tuber is dry, this can sometimes be highlighted by a wet line on the tuber and any adhering soil looking wet. Scuffing occurs when the skin is removed and internal tissues are visible. This is more of a rubbing action rather than an impact.
The factors that will influence bruise and damage susceptibility include variety, site selection, soil type, field layout, soil preparation, planting, crop Nutrition, irrigation, crop maturity, dry matter, tuber turgor, haulm destruction, soil moisture at burn off, soil moisture at harvest, temperature, storage and machinery set up and maintenance.
The season will affect many of these and be out of a growers’ control, but a reduction in susceptibility may be seen with attention to detail and thinking about bruise and damage during potato operations. The harvester set up is a key element, but there is always the trade off between stopping to adjust the harvester, and lifting pressures. The key point is to reduce drop heights as tubers move from one belt or web to another, and to stop knocks between tubers as they move on the belt. This is achieved by running belts full of tubers, or on a harvester using soil.
There is a range of information and guides to help understand bruise and damage in more detail, and to help reduce the effect at www.potato.org.uk/minimising-damage