Internal sprouting is a physiological condition where a tuber has a sprout growing either inside it or passing through an adjacent tuber. Sometimes the sprout may furrow the tuber surface. Usually a combination of factors is necessary for the problem to arise.
The greatest risk occurs where short dormant cultivars with vigorous growth are stored in warm conditions and insufficient sprout suppressant has reached the target sites. The problem is more frequent in seasons where growing conditions promote early dormancy break.
The defect is usually not possible to spot from the outside but if the sprout is near the surface there may be a tell-tale bulge or split in the outer flesh resulting in tightly wrinkled skin.
A single cut through a tuber may miss the defect and consequently several cuts are required for a full assessment.
Following best practice recommendations for CIPC will prevent the defect. Problems arise in long-term storage, where insufficient sprout suppressant has reached the target site before natural dehydration allows the crop to settle and compress target sites together.
The best control is achieved by fogging before the crop settles or spraying at store loading. If possible, choose longer dormant cultivars or those that can be stored at cooler temperatures.
If this is not possible, consider additional sprout suppressants such as maleic hydrazide.