Reducing Potato Internal Spotting

Internal Rust Spot (IRS) also known as Internal Fleck, is a physiological internal defect in which small brown spots, due to cell death, appear in the tuber. Internal Brown Spot (IBS) is any spot contained inside the vascular ring in the medullary tissue.

Crop Nutrition and Potato Internal Spotting

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 hilling or during tuber initiation.

Experience shows that a minimum of 0.15% calcium in the peel improves potato skin finish, boosts disease tolerance and minimizes 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.

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


Alongside potassium, calcium and magnesium, boron is an important element present in the cell wall. Here is 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 balanced nutrition.

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