How to reduce internal spotting in potatoes

Calcium reduces all internal disorders

Internal spotting is usually associated with either poor or interrupted supply of calcium to newly formed and expanding cells. Calcium is incorporated into cell walls and cannot be redistributed therefore it is critical to supply calcium to new cells as they are formed. Calcium can not enter cells once cell expansion takes place and too little calcium will lead to the collapse of cells and cell death leading to the visual appearance of spotting.

Internal disorders such as internal rust spot (IRS) or internal brown spot (IBS) can be reduced by a good calcium supply, in the form of calcium nitrate, at ridging or during tuber initiation.

This study demonstrates the relationship between the rate of applied calcium, calcium content of peel and the incidence of internal rust spot.

Experience shows that ensuring there is a minimum of 0.15% calcium in the peel, improves potato skin finish, boosts disease tolerance and minimises IRS. Peel analysis is a good way of confirming whether a disease or skin finish problem is calcium related. Even small amounts of calcium in the tuber can make a big difference.

Boron increases the effectiveness of calcium

Alongside potassium, calcium and magnesium, boron is an important element present in the cell wall. Here it acts as a cement between pectins, providing cohesive strength for cell tissues. Therefore boron affects tuber storage quality characteristics. Boron also affects calcium absorption, so supplies are important to ensure a balanced nutrition.

This trial shows how boron influences the calcium content of tubers and so also the incidence of internal rust spot.

Other crop management practices influencing internal spotting

• Avoiding fields, with adverse factors such poor drainage or low water holding capabilities
• Scheduling irrigation to maximize quality characteristics